Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks Sony VAIO VGN-CS33H battery. Elemental phosphorus exists in two major forms—white phosphorus and red phosphorus—but due to its high reactivity, phosphorus is never found as a free element on Earth. The first form of elemental phosphorus to be produced (white phosphorus, in 1669) emits a faint glow upon exposure to oxygen – hence its name given from Greek mythology, Φωσφόρος meaning "light-bearer" (Latin Lucifer), referring to the "Morning Star" Sony VAIO VGN-CS33H/Z battery, the planet Venus. The term "phosphorescence", meaning glow after illumination, originally derives from this property of phosphorus, although this word has since been used for a different physical process that produces a glow. The glow of phosphorus itself originates from oxidation of the white (but not red) phosphorus— a process now termed chemiluminescence Sony VAIO VGN-CS33H/B battery. The vast majority of phosphorus compounds are consumed as fertilizers. Other applications include the role of organophosphorus compounds in detergents, pesticides and nerve agents, and matches.[4] Phosphorus is essential for life. As phosphate, it is a component of DNA, RNA, ATP, and also the phospholipids that form all cell membranes. Demonstrating the link between phosphorus and life, elemental phosphorus was historically first isolated from human urine Sony VAIO VGN-CS31Z/Q battery, and bone ash was an important early phosphate source. Phosphate minerals are fossils. Low phosphate levels are an important limit to growth in some aquatic systems. The chief commercial use of phosphorus compounds for production of fertilizers is due to the need to replace the phosphorus that plants remove from the soil Sony VAIO VGN-CS31S/W battery. Characteristics Main article: Allotropes of phosphorus Physical P4 molecule Phosphorus exists as several forms (allotropes) that exhibit strikingly different properties.[5] The two most common allotropes are white phosphorus and red phosphorus. Another form, scarlet phosphorus, is obtained by allowing a solution of white phosphorus in carbon disulfide to evaporate in sunlight. Black phosphorus is obtained by heating white phosphorus under high pressures Sony VAIO VGN-CS31S/V battery (about 12,000 standard atmospheres or 1.2 gigapascals). In appearance, properties, and structure, it resembles graphite, being black and flaky, a conductor of electricity, and has puckered sheets of linked atoms. Another allotrope is diphosphorus; it contains a phosphorus dimer as a structural unit and is highly reactive. Sony VAIO VGN-CS31S/T batteryWhite phosphorus White phosphorus exposed to air glows in the darkness White phosphorus and related molecular forms The most important form of elemental phosphorus from the perspective of applications and chemical literature is white phosphorus. It consists of tetrahedral P4 molecules, in which each atom is bound to the other three atoms by a single bond. This P4 tetrahedron is also present in liquid and gaseous phosphorus up to the temperature of 800 °C when it starts decomposing to P2 molecules. Sony VAIO VGN-CS31S/R battery Solid white exists in two forms. At low-temperatures, the β form is stable. At high-temperatures α form is predominant. These forms differ in terms of the relative orientations of the constituent P4 tetrahedra. White phosphorus is the least stable, the most reactive, more volatile, less dense, and more toxic than the other allotropes. White phosphorus gradually changes to red phosphorus. This transformation Sony VAIO VGN-CS31S/P battery, which is accelerated by light and heat, and samples of white phosphorus almost always contain some red phosphorus and therefore appear yellow. For this reason, it is also called yellow phosphorus. It glows in the dark (when exposed to oxygen) with a very faint tint of green and blue, is highly flammable and pyrophoric (self-igniting) upon contact with air as well as toxic (causing severe liver damage on ingestion). Because of pyrophoricity Sony VAIO VGN-CS28 battery, white phosphorus is used as an additive in napalm. The odour of combustion of this form has a characteristic garlic smell, and samples are commonly coated with white "(di)phosphorus pentoxide", which consists of P4O10 tetrahedra with oxygen inserted between the phosphorus atoms and at their vertices. White phosphorus is insoluble in water but soluble in carbon disulfide.[8] Thermolysis (cracking) of P4 at 1100 kelvin) gives diphosphorus, P2. This species is not stable as a solid or liquid. The dimeric unit contains a triple bond and is analogous to N2 Sony VAIO VGN-CS28/Q battery. It can also be generated as a transient intermediate in solution by thermolysis of organophosphorus precursor reagents.[9] At still higher temperatures, P2 dissociates into atomic P. Although the term phosphorescence is derived from phosphorus, the reaction that gives phosphorus its glow is properly called chemiluminescence (glowing due to a cold chemical reaction), not phosphorescence (re-emitting light that previously fell onto a substance and excited it) Sony VAIO VGN-CS27 battery. Crystal structure of red phosphorus red phosphorus Red phosphorus Red phosphorus is polymeric in structure. It can be viewed as a derivative of P4 wherein one P-P bond is broken, and one additional bond is formed between the neighbouring tetrahedron resulting in a chain-like structure. Red phosphorus may be formed by heating white phosphorus to 250 °C (482 °F) or by exposing white phosphorus to sunlight Sony VAIO VGN-CS27/W battery.[10] Phosphorus after this treatment is amorphous. Upon further heating, this material crystallises. In this sense, red phosphorus is not an allotrope, but rather an intermediate phase between the white and violet phosphorus, and most of its properties have a range of values. For example, freshly prepared, bright red phosphorus is highly reactive and ignites at about 300 °C Sony VAIO VGN-CS27/R battery,[11] though it is still more stable than white phosphorus, which ignites at about 30 °C.[12] After prolonged heating or storage, the color darkens (see infobox images); the resulting product is more stable and does not spontaneously ignite in air.[13] Violet phosphorus Violet phosphorus is a form of phosphorus that can be produced by day-long annealing of red phosphorus above 550 °C. In 1865, Hittorf discovered that when phosphorus was recrystallized from molten lead, a red/purple form is obtained Sony VAIO VGN-CS27/P battery. Therefore this form is sometimes known as "Hittorf's phosphorus" (or violet or α-metallic phosphorus).[6] Crystal structure of black phosphorus Black phosphorus Black phosphorus is the least reactive allotrope and the thermodynamically stable form below 550 °C. It is also known as β-metallic phosphorus and has a structure somewhat resembling that of graphite.[14][15] High pressures are usually required to produce black phosphorus, but it can also be produced at ambient conditions using metal salts as catalysts. Sony VAIO VGN-CS27/C batteryIsotopes Main article: Isotopes of phosphorus Twenty-three isotopes of phosphorus are known,[17] including all possibilities from 24P up to 46P). Only 31P is stable and is therefore present at 100% abundance. The half-integer nuclear spin and high abundance of 31P make phosphorus-31 NMR spectroscopy a very useful analytical tool in studies of phosphorus-containing samples Sony VAIO VGN-CS26T/W battery. Two radioactive isotopes of phosphorus have half-lives that make them useful for scientific experiments. 32P has a half-life of 14.262 days and 33P has a half-life of 25.34 days. Biomolecules can be "tagged" with a radioisotope to allow for the study of very dilute samples. Radioactive isotopes of phosphorus include 32P, a beta-emitter (1.71 MeV) with a half-life of 14.3 days, which is used routinely in life-science laboratories, primarily to produce radiolabeled DNA and RNA probes Sony VAIO VGN-CS26T/V battery, e.g. for use in Northern blots or Southern blots. Because the high energy beta particles produced penetrate skin and corneas, and because any 32P ingested, inhaled, or absorbed is readily incorporated into bone and nucleic acids, Occupational Safety and Health Administration in the United States, and similar institutions in other developed countries require that a lab coat, disposable gloves and safety glasses or goggles be worn when working with 32P Sony VAIO VGN-CS26T/T battery, and that working directly over an open container be avoided in order to protect the eyes. Monitoring personal, clothing, and surface contamination is also required. In addition, due to the high energy of the beta particles, shielding this radiation with the normally used dense materials (e.g. lead), gives rise to secondary emission of X-rays via Bremsstrahlung (braking radiation). Therefore shielding must be accomplished with low density materials, e.g. Plexiglas (Lucite) Sony VAIO VGN-CS26T/R battery, other plastics, water, or (when transparency is not required), even wood.[18] 33P, a beta-emitter (0.25 MeV) with a half-life of 25.4 days. It is used in life-science laboratories in applications in which lower energy beta emissions are advantageous such as DNA sequencing. Occurrence See also Category: Phosphate minerals In terms of stellar nucleosynthesis, stable forms of phosphorus are produced in large (greater than 3 solar masses) stars by fusing two oxygen atoms together.[citation needed] This requires temperatures above 1,000 megakelvins Sony VAIO VGN-CS26T/Q battery. Phosphorus is not found free in nature, but it is widely distributed in many minerals, mainly phosphates. Phosphate rock, which is partially made of apatite (an impure tri-calcium phosphate mineral), is an important commercial source of this element. About 50 percent of the global phosphorus reserves are in the Arab nations.[19] Large deposits of apatite are located in China Sony VAIO VGN-CS26T/P battery, Russia, Morocco, Florida, Idaho, Tennessee, Utah, and elsewhere. Albright and Wilson in the United Kingdom and their Niagara Falls plant, for instance, were using phosphate rock in the 1890s and 1900s from the Îles du Connétable, Tennessee and Florida; by 1950 they were using phosphate rock mainly from Tennessee and North Africa.[20] In the early 1990s Albright and Wilson's purified wet phosphoric acid business was being adversely affected by phosphate rock sales by China and the entry of their long-standing Moroccan phosphate suppliers into the purified wet phosphoric acid business. Sony VAIO VGN-CS26T/C batteryScarcity Recent reports suggest that production of phosphorus may have peaked, leading to the possibility of global shortages by 2040.[22] In 2007, at the rate of consumption, the supply of phosphorus was estimated to run out in 345 years.[23] However, some scientists now believe that a "Peak phosphorus" will occur in 30 years and that "At current rates, reserves will be depleted in the next 50 to 100 years." Sony VAIO VGN-CS25H batteryProduction Main article: phosphoric acid The majority of phosphorus-containing compounds are produced for use as fertilisers. For this purpose, phosphate-containing minerals are converted to phosphoric acid. Two distinct routes are employed, the main one being treatment of phosphate minerals with sulfuric acid. The other process utilises white phosphorus Sony VAIO VGN-CS25H/W battery, which may be produced by reaction and distillation from very low grade phosphate sources. The white phosphorus is then oxidised to phosphoric acid and subsequently neutralised with base to give phosphate salts. Phosphoric acid obtained via white phosphorus is relatively pure and is the main source of phosphates used in detergents and other non-fertiliser applications Sony VAIO VGN-CS25H/R battery. Elemental phosphorus About 1,000,000 short tons (910,000 t) of elemental phosphorus is produced annually. Calcium phosphate (phosphate rock), mostly mined in Florida and North Africa, can be heated to 1,200–1,500 °C with sand, which is mostly SiO2, and coke (impure carbon) to produce vaporized P4. The product is subsequently condensed into a white powder under water to prevent oxidation by air. Even under water Sony VAIO VGN-CS25H/Q battery, white phosphorus is slowly converted to the more stable red phosphorus allotrope. The chemical equation for this process when starting with fluoroapatite, a common phosphate mineral, is: 4 Ca5(PO4)3F + 18 SiO2 + 30 C → 3 P4 + 30 CO + 18 CaSiO3 + 2 CaF2 Side products from this production include ferrophosphorus, a crude form of Fe2P, resulting from iron impurities in the mineral precursors. The silicate slag is a useful construction material. The fluoride is sometimes recovered for use in water fluoridation Sony VAIO VGN-CS25H/P battery. More problematic is a "mud" containing significant amounts of white phosphorus. Production of white phosphorus is conducted in large facilities in part because it is energy intensive. The white phosphorus is transported in molten form. Some major accidents have occurred during transportation, train derailments at Brownston, Nebraska and Miamisburg, Ohio led to large fires Sony VAIO VGN-CS25H/C battery. The worst incident in recent times was an environmental one in 1968 when the sea became contaminated due to spillages and/or inadequately treated sewage from a white phosphorus plant at Placentia Bay, Newfoundland.[25] Another process by which elemental phosphorus is extracted includes applying at high temperatures (1500°C): Sony VAIO VGN-CS23T/W battery2Ca3(PO4)2 + 6SiO2 + 10C --> 6CaSiO3 + 10CO + 4P4 Thermphos International is Europe's only producer of elemental phosphorus. About 6,500 short tons (5,900 t) of red phosphorus were produced in 1988. It is produced by heating white phosphorus near 270 °C. The product is treated to remove traces of white phosphorus. Red phosphorus is a component of fire retardants and striking surfaces for matches (see Applications below) Sony VAIO VGN-CS23T/Q battery. Compounds See also Category: Phosphorus compounds Oxyacids of phosphorus Phosphorous oxyacids are extensive, often commercially important, and sometimes structurally complicated. They all have acidic protons bound to oxygen atoms and some have nonacidic protons that are bonded directly to phosphorus. Although many oxyacids of phosphorus are formed, only six are important, and three of them, hypophosphorous acid, phosphorous acid and phosphoric acid are particularly important ones Sony VAIO VGN-CS23H battery. Phosphorus(V) compounds Oxides The most prevalent compounds of phosphorus are derivatives of phosphate (PO43-), a tetrahedral anion.[27] Phosphate is the conjugate base of phosphoric acid, which is produced on a massive scale for use in fertilizers. Being triprotic, phosphoric acid converts stepwise to three conjugate bases Sony VAIO VGN-CS23H/S battery: H3PO4 + H2O H3O+ + H2PO4− Ka1= 7.25×10−3 H2PO4− + H2O H3O+ + HPO42− Ka2= 6.31×10−8 HPO42− + H2O H3O+ + PO43− Ka3= 3.98×10−13 Phosphate exhibits the tendency to form chains and rings with P-O-P bonds. Many polyphosphates are known, including ATP. Polyphosphates arise by dehydration of hydrogen phosphates such as HPO42- and H2PO4-. For example, the industrially important trisodium triphosphate (also known as sodium tripolyphosphate, STPP) is produced industrially on a megatonne scale via this condensation reaction Sony VAIO VGN-CS23H/B battery: 2 Na2[(HO)PO3] + Na[(HO)2PO2] → Na5[O3P-O-P(O)2-O-PO3] + 2 H2O Phosphorus pentoxide (P4O10) is the acid anhydride of phosphoric acid, but several intermediates are known between the two. This waxy white solid reacts vigorously with water. The tetrahedral structure of P4O10 and P4S10. With metal cations, phosphate forms a variety of salts. These solids are polymeric, featuring P-O-M linkages. When the metal cation has a charge of 2+ or 3+, the salts are generally insoluble, hence they exist as common minerals. Many phosphate salts are derived from hydrogen phosphate (HPO42-) Sony VAIO VGN-CS23G battery. PCl5 and PF5 are common compounds. Both are volatile and pale or colourless. The other two halides, PBr5 and PI5PI5 are unstable. The pentachloride and pentafluoride adopt trigonal bipyramid molecular geometry and are Lewis acids. With fluoride, PF5 forms PF6–, an anion that is isoelectronic with SF6. The most important oxyhalide is phosphorus oxychloride (POCl3), which is tetrahedral Sony VAIO VGN-CS23G/W battery. Before extensive computer calculations were feasible, it was proposed that bonding in phosphorus(V) compounds involved d orbitals. It is now accepted that the bonding can be better explained by molecular orbital theory and involves only s- and p-orbitals on phosphorus. Sony VAIO VGN-CS23G/Q batteryNitrides Compounds of the formula (PNCl2)n exist mainly as rings such as the trimer hexachlorophosphazene. The phosphazenes arise by treatment of phosphorus pentachloride with ammonium chloride: PCl5 + NH4Cl → 1/n (NPCl2)n + 4 HCl The chloride groups can be replaced by alkoxide (RO-) to give rise to a family of polymers with potentially useful properties. Sony VAIO VGN-CS23G/P batterySulfides Main article: phosphorus sulfide Phosphorus forms a wide range of sulfides, where phosphorus can be P(V), P(III) or other oxidation states. Most famous is the three-fold symmetric P4S3 used in strike-anywhere matches. P4S10 and P4O10 have analogous structures.[30] Phosphorus(III) compounds Phosphine (PH3) and its organic derivatives (PR3) are structural analogues with ammonia (NH3) but the angles at phosphorus are closer to 90° for phosphine and its organic derivatives Sony VAIO VGN-CS21Z/Q battery. It is an ill-smelling, toxic compound. Phosphine is produced by hydrolysis of calcium phosphide, Ca3P2. Unlike ammonia, phosphine is oxidised by air. Phosphine is also far less basic than ammonia. All four symmetrical trihalides are well known: gaseous PF3, the yellowish liquids PCl3 and PBr3, and the solid PI3. These materials are moisture sensitive, hydrolysing to give phosphorus acid. The trichloride, a common reagent, is produced by chlorination of white phosphorus Sony VAIO VGN-CS21S/W battery: P4 + 6 Cl2 → 4 PCl3 The trifluoride is produced by from the trichloride by halide exchange. PF3 is toxic because it binds to haemoglobin. Phosphorus(III) oxide, P4O6 (also called tetraphosphorus hexoxide) is the anhydride of P(OH)3, the minor tautomer of phosphorous acid. The structure of P4O6 is like that of P4O10 less the terminal oxide groups. Mixed oxyhalides and oxyhydrides of phosphorus(III) are almost unknown Sony VAIO VGN-CS21S/V battery. Organophosphorus compounds Main article: organophosphorus compounds Compounds with P-C and P-O-C bonds are often classified as organophosphorus compounds. They are widely used commercially. The PCl3 serves as a source of P3+ in routes to organophosphorus(III) compounds. For example it is the precursor to triphenylphosphine: PCl3 + 6 Na + 3 C6H5Cl → P(C6H5)3 + 6 NaCl Treatment of phosphorus trihalides with alcohols and phenols gives phosphites, e.g. triphenylphosphite Sony VAIO VGN-CS21S/T battery: PCl3 + 3 C6H5OH → P(OC6H5)3 + 3 HCl Similar reactions occur for phosphorus oxychloride, affording triphenylphosphate: OPCl3 + 3 C6H5OH → OP(OC6H5)3 + 3 HCl Phosphorus(I) and phosphorus(II) compounds These compounds generally feature P-P bonds.[8] Examples include catenated derivatives of phosphine and organophosphines. The highly flammable gas diphosphine (P2H4) is the first of a series of derivatives of this type. Diphosphine is an analogue of hydrazine. Compounds containing P=P double bonds have also been observed, although they are rare Sony VAIO VGN-CS21S/R battery. A stable diphosphene, a derivative of phosphorus(I). Phosphides The phosphide ion is P3-. Phosphides arise by reaction of metals with red phosphorus. Salts of P3- do not exist in solution and these derivatives are refractory, reflecting their high lattice energy. Illustrated by the behaviour calcium phosphide, many metal phosphides hydrolyse in water with release of phosphine Sony VAIO VGN-CS21S/P battery: Ca3P2 + 6 H2O → 2 PH3 + 3 Ca(OH)2 Schreibersite is a naturally occurring phosphide found in meteorites. Many polyphosphides are known such as derivatives of OsP2. These can be structurally complex ranging from Na3P7 and derivatives of P264-. Often these species adopt cage-like structures that resemble fragments of violet phosphorus Sony VAIO VGN-CS19/R battery. Spelling and etymology The name Phosphorus in Ancient Greece was the name for the planet Venus and is derived from the Greek words (φως = light, φέρω = carry), which roughly translates as light-bringer or light carrier.[10] (In Greek mythology and tradition, Augerinus (Αυγερινός = morning star, in use until today), Hesperus or Hesperinus (΄Εσπερος or Εσπερινός or Αποσπερίτης = evening star, in use until today) Sony VAIO VGN-CS19/Q battery and Eosphorus (Εωσφόρος = dawnbearer, not in use for the planet after Christianity) are close homologues, and also associated with Phosphorus-the-planet). According to the Oxford English Dictionary, the correct spelling of the element is phosphorus. The word phosphorous is the adjectival form of the P3+ valence: so, just as sulfur forms sulfurous and sulfuric compounds, phosphorus forms phosphorous compounds (e.g., phosphorous acid) and P5+ valence phosphoric compounds (e.g., phosphoric acids and phosphates) Sony VAIO VGN-CS19/P battery. History and discovery Phosphorus was the 15th element to be discovered. For this reason, and also due to its use in explosives, poisons and nerve agents, it is sometimes referred to as "the Devil's element".[31] The discovery of phosphorus is credited to the German alchemist Hennig Brand in 1669, although other chemists might have discovered phosphorus around the same time Sony VAIO VGN-CS17H/W battery.[32] Brand experimented with urine, which contains considerable quantities of dissolved phosphates from normal metabolism.[10] Working in Hamburg, Brand attempted to create the fabled philosopher's stone through the distillation of some salts by evaporating urine, and in the process produced a white material that glowed in the dark and burned brilliantly Sony VAIO VGN-CS17H/Q battery. It was named phosphorus mirabilis ("miraculous bearer of light").[33] His process originally involved letting urine stand for days until it gave off a terrible smell. Then he boiled it down to a paste, heated this paste to a high temperature, and led the vapours through water, where he hoped they would condense to gold. Instead, he obtained a white, waxy substance that glowed in the dark. Brand had discovered phosphorus, the first element discovered since antiquity Sony VAIO VGN-CS16T/W battery. We now know that Brand produced ammonium sodium hydrogen phosphate, (NH4)NaHPO4. While the quantities were essentially correct (it took about 1,100 L of urine to make about 60 g of phosphorus), it was unnecessary to allow the urine to rot. Later scientists would discover that fresh urine yielded the same amount of phosphorus Sony VAIO VGN-CS16T/T battery. Robert Boyle Brand at first tried to keep the method secret,[34] but later sold the recipe for 200 thalers to D Krafft from Dresden,[10] who could now make it as well, and toured much of Europe with it, including England, where he met with Robert Boyle. The secret that it was made from urine leaked out and first Johann Kunckel (1630–1703) in Sweden (1678) and later Boyle in London (1680) also managed to make phosphorus Sony VAIO VGN-CS16T/R battery. Boyle states that Krafft gave him no information as to the preparation of phosphorus other than that it was derived from "somewhat that belonged to the body of man". This gave Boyle a valuable clue, however, so that he, too, managed to make phosphorus, and published the method of its manufacture.[10] Later he improved Brand's process by using sand in the reaction (still using urine as base material) Sony VAIO VGN-CS16T/Q battery, 4 NaPO3 + 2 SiO2 + 10 C → 2 Na2SiO3 + 10 CO + P4 Robert Boyle was the first to use phosphorus to ignite sulfur-tipped wooden splints, forerunners of our modern matches, in 1680. In 1769 Johan Gottlieb Gahn and Carl Wilhelm Scheele showed that calcium phosphate (Ca3(PO4)2) is found in bones, and they obtained phosphorus from bone ash. Antoine Lavoisier recognized phosphorus as an element in 1777.[35] Bone ash was the major source of phosphorus until the 1840s. Phosphate rock Sony VAIO VGN-CS16T/P battery, a mineral containing calcium phosphate, was first used in 1850 and following the introduction of the electric arc furnace in 1890, this became the only source of phosphorus. Phosphorus, phosphates and phosphoric acid are still obtained from phosphate rock. Phosphate rock is a major feedstock in the fertilizer industry Sony VAIO VGN-CS16T/Q battery. White phosphorus was first made commercially, for the match industry in the 19th century, by distilling off phosphorus vapour from precipitated phosphates, mixed with ground coal or charcoal, which was heated in an iron pot, in retort.[36] The precipitated phosphates were made from ground-up bones that had been de-greased and treated with strong acids Sony VAIO VGN-CS16T/P battery. Carbon monoxide and other flammable gases produced during the reduction process were burnt off in a flare stack. This process became obsolete when the submerged-arc furnace for phosphorus production was introduced to reduce phosphate rock.[37][38] The electric furnace method allowed production to increase to the point where phosphorus could be used in weapons of war.[39][40] In World War I it was used in incendiaries, smoke screens and tracer bullets Sony VAIO VGN-CS13T/W battery.[40] A special incendiary bullet was developed to shoot at hydrogen-filled Zeppelins over Britain (hydrogen being highly flammable if it can be ignited).[40] During World War II, Molotov cocktails of benzene and phosphorus were distributed in Britain to specially selected civilians within the British resistance operation, for defence; and phosphorus incendiary bombs were used in war on a large scale Sony VAIO VGN-CS13H/W battery. Burning phosphorus is difficult to extinguish and if it splashes onto human skin it has horrific effects.[8] Early matches used white phosphorus in their composition, which was dangerous due to its toxicity. Murders, suicides and accidental poisonings resulted from its use. (An apocryphal tale tells of a woman attempting to murder her husband with white phosphorus in his food, which was detected by the stew's giving off luminous steam) Sony VAIO VGN-CS13H/R battery.[39] In addition, exposure to the vapours gave match workers a severe necrosis of the bones of the jaw, the infamous "phossy jaw". When a safe process for manufacturing red phosphorus was discovered, with its far lower flammability and toxicity, laws were enacted, under the Berne Convention (1906), requiring its adoption as a safer alternative for match manufacture Sony VAIO VGN-CS13H/Q battery.[41] The toxicity of white phosphorus led to discontinuation of it use in matches.[42] In a historical coincidence, the Allies used phosphorus incendiary bombs in World War II to destroy Hamburg, the place where the "miraculous bearer of light" was first discovered.[33] The glow, the explanation, and the term derived from it It was known from early times that the green glow emanating from white phosphorus would persist for a time in a stoppered jar, but then cease. Robert Boyle in the 1680s ascribed it to "debilitation" of the air; in fact, it is oxygen being consumed Sony VAIO VGN-CS13H/P battery. By the 18th century, it was known that in pure oxygen, phosphorus does not glow at all;[43] there is only a range of partial pressure at which it does. Heat can be applied to drive the reaction at higher pressures.[44] In 1974, the glow was explained by R. J. van Zee and A. U. Khan.[39] A reaction with oxygen takes place at the surface of the solid (or liquid) phosphorus, forming the short-lived molecules HPO and P2O2 that both emit visible light Sony VAIO VGN-CS11Z/T battery. The reaction is slow and only very little of the intermediates are required to produce the luminescence, hence the extended time the glow continues in a stoppered jar. Since that time, phosphors and phosphorescence were used loosely to describe substances that shine in the dark without burning. However, as mentioned above, even though the term phosphorescence was originally coined as a term by analogy with the glow from oxidation of elemental phosphorus, is now reserved for another fundamentally different process—re-emission of light after illumination Sony VAIO VGN-CS11Z/R battery. Applications Fertiliser The dominant application of phosphorus is in fertilisers, which provides phosphate as required for all life and is often a limiting nutrient for crops. Phosphorus, being an essential plant nutrient, finds its major use as a constituent of fertilizers for agriculture and farm production in the form of concentrated phosphoric acids, which can consist of 70% to 75% P2O5 Sony VAIO VGN-CS11S/W battery. Global demand for fertilisers led to large increase in phosphate (PO43–) production in the second half of the 20th century. Due to the essential nature of phosphorus to living organisms, the low solubility of natural phosphorus-containing compounds, and the slow natural cycle of phosphorus, the agricultural industry is heavily reliant on fertilisers that contain phosphate, mostly in the form of superphosphate of lime. Superphosphate of lime is a mixture of two phosphate salt Sony VAIO VGN-CS11S/Q batterys, calcium dihydrogen phosphate Ca(H2PO4)2 and calcium sulfate dihydrate CaSO4·2H2O produced by the reaction of sulfuric acid and water with calcium phosphate. Organophosphorus compounds White phosphorus is widely used to make organophosphorus compounds, through the intermediates phosphorus chlorides and two phosphorus sulfides, phosphorus pentasulfide, and phosphorus sesquisulfide.[45] Organophosphorus compounds have many applications, including in plasticizers, flame retardants, pesticides, extraction agents Sony VAIO VGN-CS11S/P battery, and water treatment.[8] in particular the herbicide glyphosate sold under the brand name Roundup. Metallurgical aspects Phosphorus is also an important component in steel production, in the making of phosphor bronze, and in many other related products. Phosphorus is added to metallic copper during its smelting process to react with oxygen present as an impurity in copper and to produce oxygen-free copper or phosphorus-containing copper (CuOFP) alloys with a higher thermal and electrical conductivity than normal copper (Sony VAIO VGN-AW11M/H battery). Matches Match striking surface made of a mixture of red phosphorus, glue and ground glass. The glass powder is used to increase the friction. Main article: Match Phosphorus-contained matches were first produced in 1830s and contained a mixture of white phosphorus, an oxygen-releasing compound (potassium chlorate, lead dioxide or some nitrate) and a binder in their heads. They were rather sensitive to storage conditions, toxic and unsafe (Sony VAIO VGN-AW11S/B battery), as they could be lit by striking on any rough surface. Therefore, their production was gradually banned between 1872 and 1925 in different countries.[46] The international Berne Convention, adopted in 1906, prohibited the use of white phosphorus in matches. As a consequence, the 'strike-anywhere' matches were gradually replaced by 'safety matches' where white phosphorus was substituted by phosphorus sesquisulfide (P4S3), sulfur or antimony sulfide (Sony VAIO VGN-AW11Z/B battery). Such matches are hard to ignite on an arbitrary surface and require a special strip. The strip contains red phosphorus which heats up upon striking, reacts with the oxygen-releasing compound in the head and ignites the flammable material of the head.[11][45] Water softening Sodium tripolyphosphate made from phosphoric acid is used in laundry detergents in some countries, but banned for this use in others.[13] It is useful for softening water to enhance the performance of the detergents and to prevent pipe/boiler tube corrosion (Sony VAIO VGN-AW19/Q battery). Niche applications Phosphates are utilized in the making of special glasses that are used for sodium lamps.[13] Bone-ash, calcium phosphate, is used in the production of fine china.[13] Phosphoric acid made from elemental phosphorus is used in food applications such as some soda beverages. The acid is also a starting point to make food grade phosphates.[45] These include mono-calcium phosphate that is employed in baking powder and sodium tripolyphosphate and other sodium phosphates (Sony VAIO VGN-AW19 battery).[45] Among other uses these are used to improve the characteristics of processed meat and cheese. Others are used in toothpaste.[45] White phosphorus, called "WP" (slang term "Willie Peter") is used in military applications as incendiary bombs, for smoke-screening as smoke pots and smoke bombs, and in tracer ammunition. It is also a part of an obsolete M34 White Phosphorus US hand grenade (Sony VAIO VGN-AW21M/H battery). This multipurpose grenade was mostly used for signalling, smoke screens and inflammation; it could also cause severe burns and had a psychological impact on the enemy.[47][48] Military uses of white phosphorus are constrained by international law [49] In trace amounts, phosphorus is used as a dopant for n-type semiconductors. 32P and 33P are used as radioactive tracers in biochemical laboratories. Phosphate is a strong complexing agent for the hexavalent uranyl (UO22+) species and this is the reason why apatite and other natural phosphates can often be very rich in uranium (Sony VAIO VGN-AW21S/B battery). Tributylphosphate is an organophosphate soluble in kerosene and used to extract uranium in the Purex process applied in the reprocessing of spent nuclear fuel. Biological role Inorganic phosphorus in the form of the phosphate PO3− 4 is required for all known forms of life,[50] playing a major role in biological molecules such as DNA and RNA where it forms part of the structural framework of these molecules. Living cells also use phosphate to transport cellular energy in the form of adenosine triphosphate (ATP). Nearly every cellular process that uses energy obtains it in the form of ATP (Sony VAIO VGN-AW21VY/Q battery). ATP is also important for phosphorylation, a key regulatory event in cells. Phospholipids are the main structural components of all cellular membranes. Calcium phosphate salts assist in stiffening bones.[8] Living cells are defined by a membrane that separates it from its surroundings. Biological membranes are made from a phospholipid matrix and proteins, typically in the form of a bilayer. Phospholipids are derived from glycerol, such that two of the glycerol hydroxyl (OH) protons have been replaced with fatty acids as an ester, and the third hydroxyl proton has been replaced with phosphate bonded to another alcohol (Sony VAIO VGN-AW21XY/Q battery).[51] An average adult human contains about 0.7 kg of phosphorus, about 85–90% of which is present in bones and teeth in the form of apatite, and the remainder in soft tissues and extracellular fluids (~1%). The phosphorus content increases from about 0.5 weight% in infancy to 0.65–1.1 weight% in adults. Average phosphorus concentration in the blood is about 0.4 g/L, about 70% of that is organic and 30% inorganic phosphates( SONY Vaio VGN-NS38M Battery).[52] A well-fed adult in the industrialized world consumes and excretes about 1–3 grams of phosphorus per day, with consumption in the form of inorganic phosphate and phosphorus-containing biomolecules such as nucleic acids and phospholipids; and excretion almost exclusively in the form of phosphate ions such as H2PO− 4 and HPO2− 4. Only about 0.1% of body phosphate circulates in the blood, and this amount reflects the amount of phosphate available to soft tissue cells( SONY Vaio VGN-NS31S Battery). Bone and teeth enamel The main component of bone is hydroxyapatite as well as amorphous forms of calcium phosphate, possibly including carbonate. Hydroxyapatite is the main component of tooth enamel. Water fluoridation enhances the resistance of teeth to decay by the partial conversion of this mineral to the still harder material called fluoroapatite( SONY Vaio VGN-NS31M Battery):[8] Ca5(PO4)3OH + F− → Ca5(PO4)3F + OH− Phosphorus deficiency In medicine, low-phosphate syndromes are caused by malnutrition, by failure to absorb phosphate, and by metabolic syndromes that draw phosphate from the blood (such as re-feeding after malnutrition) or pass too much of it into the urine. All are characterized by hypophosphatemia, which is a condition of low levels of soluble phosphate levels in the blood serum, and therefore inside cells( SONY Vaio VGN-NS31Z Battery). Symptoms of hypophosphatemia include muscle and neurological dysfunction, and disruption of muscle and blood cells due to lack of ATP. Too much phosphate can lead to diarrhoea and calcification (hardening) of organs and soft tissue, and can interfere with the body's ability to use iron, calcium, magnesium, and zinc( SONY Vaio VGN-NS21Z Battery).[53] Phosphorus is an essential macromineral for plants, which is studied extensively in edaphology in order to understand plant uptake from soil systems. In ecological terms, phosphorus is often a limiting factor in many environments; i.e. the availability of phosphorus governs the rate of growth of many organisms. In ecosystems an excess of phosphorus can be problematic( SONY Vaio VGN-NS21M Battery), especially in aquatic systems, resulting in eutrophication which sometimes lead to algal blooms. Food sources The main food sources of phosphorus are kinds of food containing protein, for example, milk and meat. As a rule, if one holds a meal plan providing sufficient amount of protein and calcium then amount of phosphorus is also sufficient.[54] Precautions Organic compounds of phosphorus form a wide class of materials, many are required for life, but some are extremely toxic. Fluorophosphate esters are among the most potent neurotoxins known( SONY Vaio VGN-NS21S Battery). A wide range of organophosphorus compounds are used for their toxicity to certain organisms as pesticides (herbicides, insecticides, fungicides, etc.) and weaponised as nerve agents. Most inorganic phosphates are relatively nontoxic and essential nutrients.[8] The white phosphorus allotrope presents a significant hazard because it ignites in air and produces phosphoric acid residue. Chronic white phosphorus poisoning leads to necrosis of the jaw called "phossy jaw"( SONY Vaio VGN-NS12S Battery). Ingestion of white phosphorus may cause a medical condition known as "Smoking Stool Syndrome".[55] Phosphorus explosion Upon exposure to elemental phosphorus, in the past it was suggested to wash the affected area with 2% copper sulfate solution to form harmless compounds that can be washed away. According to the recent US Navy's Treatment of Chemical Agent Casualties and Conventional Military Chemical Injuries: FM8-285: Part 2 Conventional Military Chemical Injuries( SONY Vaio VGN-NS12M Battery), "Cupric (copper(II)) sulfate has been used by U.S. personnel in the past and is still being used by some nations. However, copper sulfate is toxic and its use will be discontinued. Copper sulfate may produce kidney and cerebral toxicity as well as intravascular hemolysis."[56] The manual suggests instead "a bicarbonate solution to neutralize phosphoric acid, which will then allow removal of visible white phosphorus( SONY Vaio VGN-NS11Z Battery). Particles often can be located by their emission of smoke when air strikes them, or by their phosphorescence in the dark. In dark surroundings, fragments are seen as luminescent spots. Promptly debride the burn if the patient's condition will permit removal of bits of WP (white phosphorus) that might be absorbed later and possibly produce systemic poisoning( SONY Vaio VGN-NS11M Battery). DO NOT apply oily-based ointments until it is certain that all WP has been removed. Following complete removal of the particles, treat the lesions as thermal burns."[note 1] As white phosphorus readily mixes with oils, any oily substances or ointments are not recommended until the area is thoroughly cleaned and all white phosphorus removed( SONY Vaio VGN-NS11L Battery). US DEA List I status Phosphorus can reduce elemental iodine to hydroiodic acid, which is a reagent effective for reducing ephedrine or pseudoephedrine to methamphetamine.[57] For this reason, red and white phosphorus were designated by the United States Drug Enforcement Administration as List I precursor chemicals under 21 CFR 1310.02 effective on November 17, 2001( SONY Vaio VGN-NS11J Battery).[58] As a result, in the United States, handlers of red or white phosphorus are subject to stringent regulatory controls.
Aluminium is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth's crust Sony VAIO VGN-CS33H battery. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is too reactive chemically to occur natively. Instead, it is found combined in over 270 different minerals.[4] The chief ore of aluminium is bauxite. Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials Sony VAIO VGN-CS33H/Z battery. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates. Despite its prevalence in the environment, aluminium salts are not known to be used by any form of life. In keeping with its pervasiveness, aluminium is well tolerated by plants and animals.[5] Due to their prevalence, potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interest Sony VAIO VGN-CS33H/B battery. Characteristics Etched surface from a high purity (99.9998%) aluminium bar, size 55×37 mm Physical Aluminium is a relatively soft, durable, lightweight, ductile and malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. It is nonmagnetic and does not easily ignite. A fresh film of aluminium film serves as a good reflector (approximately 92%) of visible light and an excellent reflector (as much as 98%) Sony VAIO VGN-CS31Z/Q battery of medium and far infrared radiation. The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa.[6] Aluminium has about one-third the density and stiffness of steel. It is easily machined, cast, drawn and extruded. Aluminium atoms are arranged in a face-centered cubic (fcc) structure. Aluminium has a stacking-fault energy of approximately 200 mJ/m2 Sony VAIO VGN-CS31S/W battery.[7] Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical. Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 Kelvin and a critical magnetic field of about 100 gauss (10 milliteslas). Sony VAIO VGN-CS31S/V batteryChemical Corrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper.[6] This corrosion resistance is also often greatly reduced by aqueous salts, particularly in the presence of dissimilar metals Sony VAIO VGN-CS31S/T battery. Owing to its resistance to corrosion, aluminium is one of the few metals that retain silvery reflectance in finely powdered form, making it an important component of silver-colored paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3,000–10,000 nm (far IR) regions Sony VAIO VGN-CS31S/R battery; in the 400–700 nm visible range it is slightly outperformed by tin and silver and in the 700–3000 (near IR) by silver, gold, and copper.[9] Aluminium is oxidized by water to produce hydrogen and heat: 2 Al + 3 H2O → Al2O3 + 3H2 This conversion is of interest for the production or storage of energy. Challenges include the expenses associated with the regeneration of the Al metal. Sony VAIO VGN-CS31S/P batteryIsotopes Main article: Isotopes of aluminium Aluminium has many known isotopes, whose mass numbers range from 21 to 43; however, only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2×105 y) occur naturally. 27Al has a natural abundance above 99.9%. 26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons Sony VAIO VGN-CS28 battery. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales Sony VAIO VGN-CS28/Q battery.[11] Cosmogenic 26Al was first applied in studies of the Moon and meteorites. Meteoroid fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production. After falling to Earth, atmospheric shielding drastically reduces 26Al production Sony VAIO VGN-CS27 battery, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago Sony VAIO VGN-CS27/W battery.[12] Natural occurrence See also: List of countries by bauxite production Stable aluminium is created when hydrogen fuses with magnesium either in large stars or in supernovae.[13] In the Earth's crust, aluminium is the most abundant (8.3% by weight) metallic element and the third most abundant of all elements (after oxygen and silicon).[14] Because of its strong affinity to oxygen, it is almost never found in the elemental state Sony VAIO VGN-CS27/R battery; instead it is found in oxides or silicates. Feldspars, the most common group of minerals in the Earth's crust, are aluminosilicates. Native aluminium metal can only be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes.[15] Native aluminium has been reported in cold seeps in the northeastern continental slope of the South China Sea and Chen et al. Sony VAIO VGN-CS27/P battery (2011)[16] have proposed a theory of its origin as resulting by reduction from tetrahydroxoaluminate Al(OH)4– to metallic aluminium by bacteria.[16] It also occurs in the minerals beryl, cryolite, garnet, spinel and turquoise. Impurities in Al2O3, such as chromium or iron yield the gemstones ruby and sapphire, respectively. Although aluminium is an extremely common and widespread element, the common aluminium minerals are not economic sources of the metal Sony VAIO VGN-CS27/C battery. Almost all metallic aluminium is produced from the ore bauxite (AlOx(OH)3–2x). Bauxite occurs as a weathering product of low iron and silica bedrock in tropical climatic conditions.[17] Large deposits of bauxite occur in Australia, Brazil, Guinea and Jamaica and the primary mining areas for the ore are in Australia, Brazil, China, India, Guinea, Indonesia, Jamaica, Russia and Surinam Sony VAIO VGN-CS26T/W battery. Production and refinement See also: Category:Aluminium minerals and List of countries by aluminium production Bauxite, a major aluminium ore. The red-brown colour is due to the presence of iron minerals. Aluminium forms strong chemical bonds with oxygen. Compared to most other metals, it is difficult to extract from ore, such as bauxite, due to the high reactivity of aluminum and the high melting point of most of its ores Sony VAIO VGN-CS26T/V battery. For example, direct reduction with carbon, as is used to produce iron, is not chemically possible because aluminium is a stronger reducing agent than carbon. Indirect carbothermic reduction can be carried out using carbon and Al2O3, which forms an intermediate Al4C3 and this can further yield aluminium metal at a temperature of 1900–2000 °C Sony VAIO VGN-CS26T/T battery. This process is still under development; it requires less energy and yields less CO2 than the Hall-Héroult process, the major industrial process for aluminium extraction.[18] Electrolytic smelting of alumina was originally cost-prohibitive in part because of the high melting point of alumina, or aluminium oxide, (about 2,000 °C (3,600 °F)) Sony VAIO VGN-CS26T/R battery. Many minerals, however, will dissolve into a second already molten mineral, even if the temperature of the melt is significantly lower than the melting point of the first mineral. Molten cryolite was discovered to dissolve alumina at temperatures signifcanlty lower than the melting point of pure alumina without interfering in the smelting process Sony VAIO VGN-CS26T/Q battery. In the Hall-Héroult process, alumina is first dissolved into molten cryolite with calcium fluoride and then electolytically reduced to aluminium at a temperature between 950 and 980 °C (1,740 to 1,800 °F). Cryolite is a chemical compound of aluminium and sodium fluorides: (Na3AlF6). Although cryolite is found as a mineral in Greenland, its synthetic form is used in the industry Sony VAIO VGN-CS26T/P battery. The aluminium oxide itself is obtained by refining bauxite in the Bayer process. The electrolytic process replaced the Wöhler process, which involved the reduction of anhydrous aluminium chloride with potassium. Both of the electrodes used in the electrolysis of aluminium oxide are carbon. Once the refined alumina is dissolved in the electrolyte, it disassociates and its ions are free to move around. The reaction at the cathode is Sony VAIO VGN-CS26T/C battery: Al3+ + 3 e− → Al Here the aluminium ion is being reduced. The aluminium metal then sinks to the bottom and is tapped off, usually cast into large blocks called aluminium billets for further processing. At the anode, oxygen is formed: 2 O2− → O2 + 4 e− To some extent, the carbon anode is consumed by subsequent reaction with oxygen to form carbon dioxide. The anodes in a reduction cell must therefore be replaced regularly, since they are consumed in the process Sony VAIO VGN-CS25H battery. The cathodes do erode, mainly due to electrochemical processes and metal movement. After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear. World production trend of aluminium Aluminium electrolysis with the Hall-Héroult process consumes a lot of energy, but alternative processes were always found to be less viable economically and/or ecologically Sony VAIO VGN-CS25H/W battery. The worldwide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of aluminium produced (52 to 56 MJ/kg). The most modern smelters achieve approximately 12.8 kW·h/kg (46.1 MJ/kg). (Compare this to the heat of reaction, 31 MJ/kg, and the Gibbs free energy of reaction, 29 MJ/kg.) Reduction line currents for older technologies are typically 100 to 200 kiloamperes Sony VAIO VGN-CS25H/R battery; state-of-the-art smelters operate at about 350 kA. Trials have been reported with 500 kA cells.[citation needed] The Hall-Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoope process. The process involves the electrolysis of molten aluminium with a sodium, barium and aluminium fluoride electrolyte. The resulting aluminium has a purity of 99.99%. Sony VAIO VGN-CS25H/Q batteryElectric power represents about 20% to 40% of the cost of producing aluminium, depending on the location of the smelter. Aluminium production consumes roughly 5% of electricity generated in the U.S.[21] Smelters tend to be situated where electric power is both plentiful and inexpensive, such as the United Arab Emirates with excess natural gas supplies and Iceland and Norway with energy generated from renewable sources Sony VAIO VGN-CS25H/P battery. The world's largest smelters of alumina are People's Republic of China, Russia, and Quebec and British Columbia in Canada.[21][22][23] Aluminium output in 2005 In 2005, the People's Republic of China was the top producer of aluminium with almost a one-fifth world share, followed by Russia, Canada, and the USA, reports the British Geological Survey. Over the last 50 years, Australia has become a major producer of bauxite ore and a major producer and exporter of alumina (before being overtaken by China in 2007). Sony VAIO VGN-CS25H/C batteryAustralia produced 62 million tonnes of bauxite in 2005. The Australian deposits have some refining problems, some being high in silica, but have the advantage of being shallow and relatively easy to mine.[25] Recycling Aluminium recycling code Main article: Aluminium recycling Aluminium is theoretically 100% recyclable without any loss of its natural qualities. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of aluminium in use in society Sony VAIO VGN-CS23T/W battery (i.e. in cars, buildings, electronics etc.) is 80 kg. Much of this is in more-developed countries (350–500 kg per capita) rather than less-developed countries (35 kg per capita). Knowing the per capita stocks and their approximate lifespans is important for planning recycling Sony VAIO VGN-CS23T/Q battery. Recovery of the metal via recycling has become an important facet of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to the public awareness. Recycling involves melting the scrap, a process that requires only 5% of the energy used to produce aluminium from ore, though a significant part (up to 15% of the input material) is lost as dross (ash-like oxide). Sony VAIO VGN-CS23H batteryThe dross can undergo a further process to extract aluminium. In Europe aluminium experiences high rates of recycling, ranging from 42% of beverage cans, 85% of construction materials and 95% of transport vehicles.[27] Recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium. Secondary aluminium is produced in a wide range of formats and is employed in 80% of alloy injections. Another important use is for extrusion Sony VAIO VGN-CS23H/S battery. White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium that can be extracted industrially.[28] The process produces aluminium billets, together with a highly complex waste material. This waste is difficult to manage Sony VAIO VGN-CS23H/B battery. It reacts with water, releasing a mixture of gases (including, among others, hydrogen, acetylene, and ammonia), which spontaneously ignites on contact with air;[29] contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, the waste has found use as a filler in asphalt and concrete. Sony VAIO VGN-CS23G batteryCompounds Oxidation state +3 The vast majority of compounds, including all Al-containing minerals and all commercially significant aluminium compounds, feature aluminium in the oxidation state 3+. The coordination number of such compounds varies, but generally Al3+ is six-coordinate or tetracoordinate. Almost all compounds of aluminium(III) are colorless. Sony VAIO VGN-CS23G/W batteryHalides All four trihalides are well known. Unlike the structures of the three heavier trihalides, aluminium fluoride (AlF3) features six-coordinate Al. The octahedral coordination environment for AlF3 is related to the compactness of fluoride ion, six of which can fit around the small Al3+ centre. AlF3 sublimes (with cracking) at 1,291 °C (2,356 °F) Sony VAIO VGN-CS23G/Q battery. With heavier halides, the coordination numbers are lower. The other trihalides are dimeric or polymeric with tetrahedral Al centers. These materials are prepared by treating aluminium metal with the halogen, although other methods exist. Acidification of the oxides or hydroxides affords hydrates. In aqueous solution Sony VAIO VGN-CS23G/P battery, the halides often form mixtures, generally containing six-coordinate Al centres, which are feature both halide and aquo ligands. When aluminium and fluoride are together in aqueous solution, they readily form complex ions such as [AlF(H2O)5]2+, AlF3(H2O)3, and [AlF6]3−. In the case of chloride, polyaluminium clusters are formed such as [Al13O4(OH)24(H2O)12]7+ Sony VAIO VGN-CS21Z/Q battery. Oxide and hydroxides Aluminium forms one stable oxide, known by its mineral name corundum. Sapphire and ruby are impure corundum contaminated with trace amounts of other metals. The two oxide-hydroxides (AlO(OH) are boehmite and diaspore. There are three trihydroxides: bayerite, gibbsite, and nordstrandite Sony VAIO VGN-CS21S/W battery, which differ in their crystalline structure (polymorphs). Most are produced from ores by a variety of wet processes using acid and base. Heating the hydroxides leads to formation of corundrum. These materials are of central importance to the production of aluminium and are themselves extremely useful Sony VAIO VGN-CS21S/V battery. Carbide, nitride, and related materials Aluminium carbide (Al4C3) is made by heating a mixture of the elements above 1,000 °C (1,832 °F). The pale yellow crystals consist of tetrahedral aluminium centres. It reacts with water or dilute acids to give methane. The acetylide, Al2(C2)3, is made by passing acetylene over heated aluminium Sony VAIO VGN-CS21S/T battery. Aluminium nitride (AlN) is the only nitride known for aluminium. Unlike the oxides it features tetrahedral Al centres. It can be made from the elements at 800 °C (1,472 °F). It is air-stable material with a usefully high thermal conductivity. Aluminium phosphide (AlP) is made similarly, and hydrolyses to give phosphine Sony VAIO VGN-CS21S/R battery: AlP + 3 H2O → Al(OH)3 + PH3 Organoaluminium compounds and related hydrides Main article: Organoaluminium compound Structure of trimethylaluminium, a compound that features five-coordinate carbon. A variety of compounds of empirical formula AlR3 and AlR1.5Cl1.5 exist.[31] These species usually feature tetrahedral Al centres, e.g. "trimethylaluminium" has the formula Al2(CH3)6 (see figure). With large organic groups, triorganoaluminium exist as three-coordinate monomers, such as triisobutylaluminium Sony VAIO VGN-CS21S/P battery. Such compounds are widely used in industrial chemistry, despite the fact that they are often highly pyrophoric. Few analogues exist between organoaluminium and organoboron compounds except for large organic groups. The important aluminium hydride is lithium aluminium hydride (LiAlH4), which is used in as a reducing agent in organic chemistry. It can be produced from lithium hydride and aluminium trichloride Sony VAIO VGN-CS215J/R battery: 4 LiH + AlCl3 → LiAlH4 + 3 LiCl Several useful derivatives of LiAlH4 are known, e.g. Sodium bis(2-methoxyethoxy)dihydridoaluminate. The simplest hydride, aluminium hydride or alane, remains a laboratory curiosity. It is a polymer with the formula (AlH3)n, in contrast to the corresponding boron hydride with the formula (BH3)2 Sony VAIO VGN-CS19/W battery. Oxidation states +1 and +2 Although the great majority of aluminium compounds feature Al3+ centres, compounds with lower oxidation states are known and sometime of significance as precursors to the Al3+ species. Aluminium(I) AlF, AlCl and AlBr exist in the gaseous phase when the tri-halide is heated with aluminium. The composition AlI is unstable at room temperature with respect to the triiodide: Sony VAIO VGN-CS19/R battery3 AlI → AlI3 + 2 Al A stable derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al4I4(NEt3)4. Also of theoretical interest but only of fleeting existence are Al2O and Al2S is made by heating the normal oxide, Al2O3, with silicon at 1,800 °C (3,272 °F) in a vacuum.[32] Such materials quickly disproportionates to the starting materials Sony VAIO VGN-CS19/Q battery. Aluminium(II) Very simple Al(II) compounds are invoked or observed in the reactions of Al metal with oxidants. For example, aluminium monoxide, AlO, has been detected in the gas phase after explosion[33] and in stellar absorption spectra.[34] More thoroughly investigated are compounds of the formula R4Al2 where R is a large organic ligand. Sony VAIO VGN-CS19/P batteryAnalysis The presence of aluminium can be detected in qualitative analysis using aluminon. Applications General use Aluminium is the most widely used non-ferrous metal.[36] Global production of aluminium in 2005 was 31.9 million tonnes. It exceeded that of any other metal except iron (837.5 million tonnes).[37] Forecast for 2012 is 42–45 million tonnes, driven by rising Chinese output. Sony VAIO VGN-CS17H/W batteryAluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common aluminium foils and beverage cans are alloys of 92% to 99% aluminium.[39] The main alloying agents are copper, zinc, magnesium, manganese, and silicon (e.g., duralumin) and the levels of these other metals are in the range of a few percent by weight. Sony VAIO VGN-CS17H/Q batteryHousehold aluminium foil Aluminium-bodied Austin "A40 Sports" (circa 1951) Aluminium slabs being transported from a smelter Some of the many uses for aluminium metal are in: Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, etc.) as sheet, tube, castings, etc. Packaging (cans, foil, etc.) Construction (windows, doors, siding, building wire, etc.).[41] A wide range of household items, from cooking utensils to baseball bats, watches.[42] Street lighting poles, sailing ship masts, walking poles, etc Sony VAIO VGN-CS16T/W battery. Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment. Electrical transmission lines for power distribution MKM steel and Alnico magnets Super purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs. Heat sinks for electronic appliances such as transistors and CPUs. Substrate material of metal-core copper clad laminates used in high brightness LED lighting Sony VAIO VGN-CS16T/T battery. Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite. Aluminium can be reacted with hydrochloric acid or with sodium hydroxide to produce hydrogen gas. A variety of countries, including France, Italy, Poland, Finland, Romania, Israel, and the former Yugoslavia, have issued coins struck in aluminium or aluminium-copper alloys. Sony VAIO VGN-CS16T/R batterySome guitar models sports aluminium diamond plates on the surface of the instruments, usually either chrome or black. Kramer Guitars and Travis Bean are both known for having produced guitars with necks made of aluminium, which gives the instrument a very distinct sound Sony VAIO VGN-CS16T/Q battery. Aluminium is usually alloyed – it is used as pure metal only when corrosion resistance and/or workability is more important than strength or hardness. A thin layer of aluminium can be deposited onto a flat surface by physical vapour deposition or (very infrequently) chemical vapour deposition or other chemical means to form optical coatings and mirrors Sony VAIO VGN-CS16T/P battery. Aluminium compounds Because aluminium is abundant and most of its derivative exhibit low toxicity, the compounds of aluminium enjoy wide and sometimes large-scale applications. Alumina Main article: Aluminium oxide Aluminium oxide (Al2O3) and the associated oxy-hydroxides and trihydroxides are produced or extracted from minerals on a large scale. The great majority of this material is converted to metallic aluminium Sony VAIO VGN-CS13T/W battery. About 10% of the production capacity is used for other applications. A major use is as an absorbent, for example alumina will remove water from hydrocarbons, to enable subsequent processes that are poisoned by moisture. Aluminium oxides are common catalysts for industrial processes, e.g. the Claus process for converting hydrogen sulfide to sulfur in refineries and for the alkylation of amines Sony VAIO VGN-CS13H/W battery. Many industrial catalysts are "supported", meaning generally that an expensive catalyst (e.g., platinum) is dispersed over a high surface area material such as alumina. Being a very hard material (Mohs hardness 9), alumina is widely used as an abrasive and the production of applications that exploit its inertness, e.g., in high pressure sodium lamps Sony VAIO VGN-CS13H/R battery. Sulfates Several sulfates of aluminium find applications. Aluminium sulfate (Al2(SO4)3(H2O)18) is produced on the annual scale of several billions of kilograms. About half of the production is consumed in water treatment. The next major application is in the manufacture of paper. It is also used as a mordant Sony VAIO VGN-CS13H/Q battery, in fire extinguisher, as a food additive, in fireproofing, and in leather tanning. Aluminium ammonium sulfate, which is also called ammonium alum, (NH4)Al(SO4)2·12H2O, is used as a mordant and in leather tanning.[5] Aluminium potassium sulfate ([Al(K)](SO4)2)(H2O)12 is used similarly. The consumption of both alums is declining Sony VAIO VGN-CS13H/P battery. Chlorides Aluminium chloride (AlCl3) is used in petroleum refining and in the production of synthetic rubber and polymers. Although it has a similar name, aluminium chlorohydrate has fewer and very different applications, e.g. as a hardening agent and an antiperspirant. It is an intermediate in the production of aluminium metal Sony VAIO VGN-CS11Z/T battery. Niche compounds Given the scale of aluminium compounds, a small scale application could still involve thousands of tonnes. One of the many compounds used at this intermediate level include aluminium acetate, a salt used in solution as an astringent. Aluminium borate (Al2O3·B2O3) is used in the production of glass and ceramics Sony VAIO VGN-CS11Z/R battery. Aluminium fluorosilicate (Al2(SiF6)3) is used in the production of synthetic gemstones, glass and ceramic. Aluminium phosphate (AlPO4) is used in the manufacture: of glass and ceramic, pulp and paper products, cosmetics, paints and varnishes and in making dental cement. Aluminium hydroxide (Al(OH)3) is used as an antacid, as a mordant, in water purification Sony VAIO VGN-CS11S/W battery, in the manufacture of glass and ceramic and in the waterproofing of fabrics. Lithium aluminium hydride is a powerful reducing agent used in organic chemistry. Organoaluminiums are used as Lewis acids and cocatalysts. For example, methylaluminoxane is a cocatalyst for Ziegler-Natta olefin polymerization to produce vinyl polymers such as polyethene Sony VAIO VGN-CS11S/Q battery. Aluminium alloys in structural applications Main article: Aluminium alloy Aluminium foam Aluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by names indicating their main alloying constituents (DIN and ISO). The strength and durability of aluminium alloys vary widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processes Sony VAIO VGN-CS11S/P battery. A lack of knowledge of these aspects has from time to time led to improperly designed structures and gained aluminium a bad reputation. One important structural limitation of aluminium alloys is their fatigue strength. Unlike steels, aluminium alloys have no well-defined fatigue limit, meaning that fatigue failure eventually occurs, under even very small cyclic loadings. This implies that engineers must assess these loads and design for a fixed life rather than an infinite life (Sony VAIO VGN-AW11M/H battery). Another important property of aluminium alloys is their sensitivity to heat. Workshop procedures involving heating are complicated by the fact that aluminium, unlike steel, melts without first glowing red. Forming operations where a blow torch is used therefore require some expertise, since no visual signs reveal how close the material is to melting. Aluminium alloys, like all structural alloys (Sony VAIO VGN-AW11S/B battery), also are subject to internal stresses following heating operations such as welding and casting. The problem with aluminium alloys in this regard is their low melting point, which make them more susceptible to distortions from thermally induced stress relief. Controlled stress relief can be done during manufacturing by heat-treating the parts in an oven, followed by gradual cooling—in effect annealing the stresses (Sony VAIO VGN-AW11Z/B battery). The low melting point of aluminium alloys has not precluded their use in rocketry; even for use in constructing combustion chambers where gases can reach 3500 K. The Agena upper stage engine used a regeneratively cooled aluminium design for some parts of the nozzle, including the thermally critical throat region. Another alloy of some value is aluminium bronze (Cu-Al alloy) (Sony VAIO VGN-AW19/Q battery). History The statue of the Anteros (commonly mistaken for either The Angel of Christian Charity or Eros) in Piccadilly Circus, London, was made in 1893 and is one of the first statues to be cast in aluminium. Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a styptic. In 1761, Guyton de Morveau suggested calling the base alum alumine (Sony VAIO VGN-AW19 battery). In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first termed alumium and later aluminum (see etymology section, below). The metal was first produced in 1825 in an impure form by Danish physicist and chemist Hans Christian Ørsted. He reacted anhydrous aluminium chloride with potassium amalgam, yielding a lump of metal looking similar to tin (Sony VAIO VGN-AW21M/H battery).[45] Friedrich Wöhler was aware of these experiments and cited them, but after redoing the experiments of Ørsted he concluded that this metal was pure potassium. He conducted a similar experiment in 1827 by mixing anhydrous aluminium chloride with potassium and yielded aluminium.[45] Wöhler is generally credited with isolating aluminium (Latin alumen, alum) (Sony VAIO VGN-AW21S/B battery), but also Ørsted can be listed as its discoverer.[46] Further, Pierre Berthier discovered aluminium in bauxite ore and successfully extracted it.[47] Frenchman Henri Etienne Sainte-Claire Deville improved Wöhler's method in 1846, and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium. (Sony VAIO VGN-AW21VY/Q battery) Deville likely also conceived the idea of the electrolysis of aluminium oxide dissolved in cryolite; Charles Martin Hall and Paul Héroult might have developed the more practical process after Deville. Before the Hall-Héroult process was developed in the late 1880s, aluminium was exceedingly difficult to extract from its various ores. This made pure aluminium more valuable than gold. (Sony VAIO VGN-AW21XY/Q battery)Bars of aluminium were exhibited at the Exposition Universelle of 1855.[50] Napoleon III, Emperor of France, is reputed to have given a banquet where the most honoured guests were given aluminium utensils, while the others made do with gold.[51][52] Aluminium was selected as the material to be used for the 100 ounce (2.8 kg) capstone of the Washington Monument in 1884, a time when one ounce (30 grams) cost the daily wage of a common worker on the project (Sony VAIO VGN-AW21Z/B battery);[53] The capstone, which was set in place on December 6, 1884, in an elaborate dedication ceremony, was the largest single piece of aluminium cast at the time, when aluminium was as expensive as silver.[53] The Cowles companies supplied aluminium alloy in quantity in the United States and England using smelters like the furnace of Carl Wilhelm Siemens by 1886. (Sony VAIO VGN-AW31M/H battery)Charles Martin Hall of Ohio in the U.S. and Paul Héroult of France independently developed the Hall-Héroult electrolytic process that made extracting aluminium from minerals cheaper and is now the principal method used worldwide. Hall's process,[57] in 1888 with the financial backing of Alfred E. Hunt, started the Pittsburgh Reduction Company today known as Alcoa. (Sony VAIO VGN-AW31S/B battery) Héroult's process was in production by 1889 in Switzerland at Aluminium Industrie, now Alcan, and at British Aluminium, now Luxfer Group and Alcoa, by 1896 in Scotland.[58] By 1895, the metal was being used as a building material as far away as Sydney, Australia in the dome of the Chief Secretary's Building. Many navies have used an aluminium superstructure for their vessels (Sony VAIO VGN-AW31XY/Q battery); the 1975 fire aboard USS Belknap that gutted her aluminium superstructure, as well as observation of battle damage to British ships during the Falklands War, led to many navies switching to all steel superstructures. The Arleigh Burke class was the first such U.S. ship, being constructed entirely of steel (Sony VAIO VGN-AW31ZJ/B battery). Aluminium wire was once widely used for domestic electrical wiring. Owing to corrosion-induced failures, a number of fires resulted. This discontinuation thus illustrates one failed application of the otherwise highly useful metal. Etymology Two variants of the metal's name are in current use, aluminium and aluminum (besides the obsolete alumium) (Sony VAIO VGN-AW41JF battery). The International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as the standard international name for the element in 1990 but, three years later, recognized aluminum as an acceptable variant. Hence their periodic table includes both.[59] IUPAC prefers the use of aluminium in its internal publications, although nearly as many IUPAC publications use the spelling aluminum. (Sony VAIO VGN-AW41MF/H battery)Most countries use the spelling aluminium. In the United States, the spelling aluminum predominates.[14][61] The Canadian Oxford Dictionary prefers aluminum, whereas the Australian Macquarie Dictionary prefers aluminium. In 1926, the American Chemical Society officially decided to use aluminum in its publications; American dictionaries typically label the spelling aluminium as a British variant. (Sony VAIO VGN-AW41MF battery)The name aluminium derives from its status as a base of alum. It is borrowed from Old French; its ultimate source, alumen, in turn is a Latin word that literally means "bitter salt".[62] The earliest citation given in the Oxford English Dictionary for any word used as a name for this element is alumium, which British chemist and inventor Humphry Davy employed in 1808 for the metal he was trying to isolate electrolytically from the mineral alumina (Sony VAIO VGN-AW41XH/Q battery). The citation is from the journal Philosophical Transactions of the Royal Society of London: "Had I been so fortunate as to have obtained more certain evidences on this subject, and to have procured the metallic substances I was in search of, I should have proposed for them the names of silicium, alumium, zirconium, and glucium." (Sony VAIO VGN-AW41XH battery)Davy settled on aluminum by the time he published his 1812 book Chemical Philosophy: "This substance appears to contain a peculiar metal, but as yet Aluminum has not been obtained in a perfectly free state, though alloys of it with other metalline substances have been procured sufficiently distinct to indicate the probable nature of alumina." (Sony VAIO VGN-AW41ZF/B battery) But the same year, an anonymous contributor to the Quarterly Review, a British political-literary journal, in a review of Davy's book, objected to aluminum and proposed the name aluminium, "for so we shall take the liberty of writing the word, in preference to aluminum, which has a less classical sound." (Sony VAIO VGN-AW41ZF battery)The -ium suffix conformed to the precedent set in other newly discovered elements of the time: potassium, sodium, magnesium, calcium, and strontium (all of which Davy isolated himself). Nevertheless, -um spellings for elements were not unknown at the time, as for example platinum, known to Europeans since the 16th century, molybdenum, discovered in 1778, and tantalum, discovered in 1802. HP Pavilion dv6-1299lx battery The -um suffix is consistent with the universal spelling alumina for the oxide, as lanthana is the oxide of lanthanum, and magnesia, ceria, and thoria are the oxides of magnesium, cerium, and thorium respectively. The spelling used throughout the 19th century by most U.S. chemists was aluminium, but common usage is less clear HP Pavilion dv6-1299ez battery.[67] The aluminum spelling is used in the Webster's Dictionary of 1828. In his advertising handbill for his new electrolytic method of producing the metal 1892, Charles Martin Hall used the -um spelling, despite his constant use of the -ium spelling in all the patents[57] he filed between 1886 and 1903.[68] It has consequently been suggested that the spelling reflects an easier to pronounce word with one fewer syllable HP Pavilion dv6-1299es battery, or that the spelling on the flier was a mistake. Hall's domination of production of the metal ensured that the spelling aluminum became the standard in North America; the Webster Unabridged Dictionary of 1913, though, continued to use the -ium version. Health concerns NFPA 704 000 Fire diamond for aluminium shot Despite its natural abundance, aluminium has no known function in biology. It is remarkably nontoxic HP Pavilion dv6-1299er battery, aluminium sulfate having an LD50 of 6207 mg/kg (oral, mouse), which corresponds to 500 grams for a 80 kg person.[5] Despite the extremely low acute toxicity, the health effects of aluminium are of interest in view of the widespread occurrence of the element in the environment and in commerce HP Pavilion dv6-1299eo battery. Some toxicity can be traced to deposition in bone and the central nervous system, which is particularly increased in patients with reduced renal function. Because aluminium competes with calcium for absorption, increased amounts of dietary aluminium may contribute to the reduced skeletal mineralization (osteopenia) observed in preterm infants and infants with growth retardation HP Pavilion dv6-1299ef battery. In very high doses, aluminium can cause neurotoxicity, and is associated with altered function of the blood-brain barrier.[69] A small percentage of people are allergic to aluminium and experience contact dermatitis, digestive disorders, vomiting or other symptoms upon contact or ingestion of products containing aluminium HP Pavilion dv6-1299ea battery, such as deodorants or antacids. In those without allergies, aluminium is not as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts.[70] Although the use of aluminium cookware has not been shown to lead to aluminium toxicity in general, excessive consumption of antacids containing aluminium compounds and excessive use of aluminium-containing antiperspirants provide more significant exposure levels HP Pavilion dv6-1295el battery. Studies have shown that consumption of acidic foods or liquids with aluminium significantly increases aluminium absorption,[71] and maltol has been shown to increase the accumulation of aluminium in nervous and osseus tissue.[72] Furthermore, aluminium increases estrogen-related gene expression in human breast cancer cells cultured in the laboratory. HP Pavilion dv6-1291es battery The estrogen-like effects of these salts have led to their classification as a metalloestrogen. The effects of aluminium in antiperspirants has been examined over the course of decades with little evidence of skin irritation.[5] Nonetheless, its occurrence in antiperspirants, dyes (such as aluminium lake), and food additives is controversial in some quarters HP Pavilion dv6-1290ev battery. Although there is little evidence that normal exposure to aluminium presents a risk to healthy adults,[74] some studies point to risks associated with increased exposure to the metal.[75] Aluminium in food may be absorbed more than aluminium from water.[76] Some researchers have expressed concerns that the aluminium in antiperspirants may increase the risk of breast cancer, HP Pavilion dv6-1290es battery and aluminium has controversially been implicated as a factor in Alzheimer's disease.[78] The Camelford water pollution incident involved a number of people consuming aluminium sulfate. Investigations of the long-term health effects are still ongoing, but elevated brain aluminium concentrations have been found in post-mortem examinations of victims, and further research to determine if there is a link with cerebral amyloid angiopathy has been commissioned HP Pavilion dv6-1290en battery.[79] According to The Alzheimer's Society, the overwhelming medical and scientific opinion is that studies have not convincingly demonstrated a causal relationship between aluminium and Alzheimer's disease.[80] Nevertheless, some studies, such as those on the PAQUID cohort,[81] cite aluminium exposure as a risk factor for Alzheimer's disease HP Pavilion dv6-1290ec battery. Some brain plaques have been found to contain increased levels of the metal.[82] Research in this area has been inconclusive; aluminium accumulation may be a consequence of the disease rather than a causal agent. In any event, if there is any toxicity of aluminium, it must be via a very specific mechanism, since total human exposure to the element in the form of naturally occurring clay in soil and dust is enormously large over a lifetime. HP Pavilion dv6-1288la battery Scientific consensus does not yet exist about whether aluminium exposure could directly increase the risk of Alzheimer's disease.[80] Effect on plants Aluminium is primary among the factors that reduce plant growth on acid soils. Although it is generally harmless to plant growth in pH-neutral soils, the concentration in acid soils of toxic Al3+ cations increases and disturbs root growth and function. HP Pavilion dv6-1210ee batteryMost acid soils are saturated with aluminium rather than hydrogen ions. The acidity of the soil is therefore a result of hydrolysis of aluminium compounds.[89] This concept of "corrected lime potential"[90] to define the degree of base saturation in soils became the basis for procedures now used in soil testing laboratories to determine the "lime requirement"[91] of soils HP Pavilion dv6-1210eg battery.[92] Wheat's adaptation to allow aluminium tolerance is such that the aluminium induces a release of organic compounds that bind to the harmful aluminium cations. Sorghum is believed to have the same tolerance mechanism. The first gene for aluminium tolerance has been identified in wheat. It was shown that sorghum's aluminium tolerance is controlled by a single gene, as for wheat.[93] This is not the case in all plants HP Pavilion dv6-1210ek battery. Lead ( /ˈlɛd/) is a main-group element in the carbon group with the symbol Pb (from Latin: plumbum) and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid HP Pavilion dv6-1210er battery. Lead is used in building construction, lead-acid batteries, bullets and shots, weights, as part of solders, pewters, fusible alloys and as a radiation shield. Lead has the highest atomic number of all of the stable elements, although the next higher element, bismuth, has a half-life that is so long (much longer than the age of the universe) that it can be considered stable HP Pavilion dv6-1210es battery. Its four stable isotopes have 82 protons, a magic number in the nuclear shell model of atomic nuclei. Lead, at certain exposure levels, is a poisonous substance to animals as well as for human beings. It damages the nervous system and causes brain disorders. Excessive lead also causes blood disorders in mammals. Like the element mercury, another heavy metal, lead is a neurotoxin that accumulates both in soft tissues and the bones HP Pavilion dv6-1210et battery. Lead poisoning has been documented from ancient Rome, ancient Greece, and ancient China. Characteristics A sample of recently solidified lead (from a molten state) Lead is a bright and silvery (with a very slight shade of blue[1]) metal in a dry atmosphere; upon contact with air, it begins to tarnish. It has a few characteristic properties: high density, softness, ductility and malleability, poor electrical conductivity (compared to other metals), high resistance to corrosion, and ability to react with organic chemicals. HP Pavilion dv6-1210ew batteryVarious traces of other metals change its properties significantly: addition of small amounts of antimony or copper increases hardness and improves the corrosion reflection from sulfuric acid for lead.[1] A few other metals also improve only hardness and fight the metal fatigue, such as cadmium, tin, or tellurium HP Pavilion dv6-1210ez battery; metals like sodium or calcium also have this ability, but they weaken the chemical stability.[1] Finally, zinc and bismuth simply impair the corrosion resistance (0.1% bismuth content prevent lead from the industrial usage).[1] In return, lead impurities mostly worsen the quality of industrial materials, although there are exceptions: for example, small amounts of lead improve the ductility of steel. HP Pavilion dv6-1210sa battery [1] Lead has only one common allotrope, which is face-centered cubic, with the lead–lead distance being 349 pm.[2] At 327.5 °C (621.5 °F),[3] lead melts; the melting point is above that of tin (232 °C, 449.5 °F),[3] but significantly below that of germanium (938 °C, 1721 °F).[4] The boiling point of lead is 1749 °C (3180 °F),[5] which is below than those of both tin (2602 °C, 4716 °F)[3] and germanium (2833 °C, 5131 °F) HP Pavilion dv6-1210sb battery.[4] Densities get simply bigger down the group: the Ge and Sn values (5.23[6] and 7.29 g·cm−3,[7] respectively) are significantly below that of lead: 11.32 g·cm−3.[6] A lead atom has 82 electrons, having an electronic configuration of [Xe]4f145d106s26p2. In its compounds, lead (unlike the other group 14 elements) most commonly loses its two and not four outermost electrons, becoming lead(II) ions, Pb2+. Such unusual behavior is rationalized by considering the inert pair effect HP Pavilion dv6-1210sf battery, which occurs because of the stabilization of 6s-orbital due to relativistic effects, which are stronger closer to the bottom of the periodic table.[8] Tin shows a weaker such effect: tin(II) is still a reducer.[8] The figures for electrode potential show that lead is only slightly easier to oxidize than hydrogen. Lead thus can dissolve in acids, but this is often impossible due to specific problems (such as insoluble salts formation) HP Pavilion dv6-1210sl battery.[9] Powdered lead burns with a bluish-white flame. As with many metals, finely divided powdered lead exhibits pyrophoricity.[10] Toxic fumes are released when lead is burned. Isotopes Main article: Isotopes of lead Lead occurs naturally on Earth exclusively in the form of four isotopes: lead-204, -206, -207, and -208.[11] All four can be radioactive as the hypothetical alpha decay of any would release energy, but the lower half-life limit has been put only for lead-204: over 1.4×1017 years HP Pavilion dv6-1210sr battery.[12] This effect is, however, so weak that natural lead makes no radiation hazard. Three of them are also found in three of the four major decay chains: lead-206, -207 and -208 are final decay products of uranium-238, uranium-235, and thorium-232, respectively. Since the amounts of them in nature depend also on other elements' presence HP Pavilion dv6-1210sv battery, the isotopic composition of natural lead varies by sample: in particular, the relative amount of lead-206 varies between 20.84% and 27.78%.[11] Aside from the stable ones, thirty-four radioisotopes have been synthesized: they have the mass numbers of 178–215.[12] Lead-205 is the most stable radioisotope of lead, with a half-life of over 107 years. 47 nuclear isomers (long-lived excited nuclear states), corresponding to 24 lead isotopes, have been characterized. The most long-lived is lead-204m2 (half-life of about 1.1 hours). HP Pavilion dv6-1210tx batteryChemical reactivity Lead is chemically a post-transition metal and belongs to the group 14 of the periodic table. It shows two main oxidation states, which are +2 and +4. The former is more stable, while the +4 oxidation state, favored for the rest of the group, is an oxidizer; lead(IV) ions exist only in highly acidic solutions HP Pavilion dv6-1211ax battery.[8] Cold thoroughly crushed lead may ignite in the air, as it is attacked by oxygen in it; compact lead only form a protective oxide layer. Melted lead is oxidized in the air to become lead monoxide. At 430 °C (810 °F), it is further oxidized to become trilead tetroxide, which decomposes at 550 °C (1020 °F) to turn back into PbO. All chalcogens oxidize lead upon heating; during the reaction with sulfur, the metal may be heated to get red. HP Pavilion dv6-1211er batteryFluorine does not oxidize cold lead. Hot lead can be oxidized, but the formation on a protective halide layer lowers the intensity of the reaction above 100 °C (210 °F). The reaction with chlorine is similar: thanks to the chloride layer, lead persistence against chlorine surpasses those of copper or steel up to 300 °C (570 °F). HP Pavilion dv6-1211sa batteryWater in presence of oxygen attacks lead to start an accelerating reaction. Presence of carbonates or sulfates lead to formation of insoluble lead salts, which prevent the metal from corrosion. So does carbon dioxide, as the insoluble lead carbonate is formed; however, excess of the gas leads to the formation of the soluble bicarbonate HP Pavilion dv6-1211sg battery; this dangers the usage of lead pipes.[9] Lead dissolves in organic acids (in presence of oxygen) and concentrated (≥80%) sulfuric acid thanks to complexation; however, it is only weakly affected by hydrochloric acid and is stable against hydrofluoric acid, as the corresponding halides are weakly soluble. Lead also dissolves in quite concentrated alkalis (≥10%) thanks to the amphoteric character and solubility of plumbites HP Pavilion dv6-1211tx battery.[9] Compounds Main article: Compounds of lead Oxides and sulfide There are three oxides known: PbO, Pb3O4 (sometimes called "minium"), and PbO2. The former has two allotropes: α-PbO and β-PbO, both with layer structure and tetracoordinated lead. The alpha allotrope is red-colored and has the Pb–O distance of 230 pm; the beta allotrope is yellow-colored and has the Pb–O distance of 221 and 249 pm (due to asymmetry) HP Pavilion dv6-1212sl battery.[14] Thanks to the similarity, both allotropes can exist under standard conditions (beta with small (10-5 relative) impurities, such as Si, Ge, Mo, etc.). PbO reacts with acids to form salts, and with alkalies to give plumbites, [Pb(OH)3]- or [Pb(OH)4]2-.[15] The dioxide may be prepared by, for example, halogenization of lead(II) salts. Regardless the allotrope, it has a black-brown color HP Pavilion dv6-1212tx battery. The alpha allotrope is rhombohedral, and the beta allotrope is tetragonal.[15] Both allotropes are black-brown in color and always contain some water, which cannot be removed, as heating also causes decomposition (to PbO and Pb3O4). The dioxide is a powerful oxidizer: it can oxidize hydrochloric and sulfuric acids. It does not reacts with alkaline solution, but reacts with solid alkalies to give hydroxyplumbates HP Pavilion dv6-1213ax battery, or with basic oxides to give plumbates.[15] Reaction of lead with sulfur or hydrogen sulfide yields lead sulfide. The solid has the NaCl-like striucture (simple cubic), which it keeps up to the melting point, 1114 °C (2037 °F). If the heating occurs in presence of air, the compounds decomposes to give the monoxide and the sulfate HP Pavilion dv6-1213tx battery.[16] The compounds is almost insoluble in water, weak acids, and (NH4)2S/(NH4)2S2 solution is the key for separation of lead from analythical groups I to III elements, tin, arsenic, and antimony. The compounds, however, dissolves in nitric and hydrochloric acids, to give elemental sulfur and hydrogen sulfide, respectively.[16] Heating a mixture of the monoxide and the sulfide heated together forms the metal. HP Pavilion dv6-1214ax battery2 PbO + PbS → 3 Pb + SO2↑ Halides and other salts Heating lead carbonate with hydrogen fluoride yields the hydrofluoride, which decomposes to the difluoride when melts. This white crystalline powder is more soluble than the diiodide, but less than the dibromide and the dichloride. No coordinated lead fluorides exist (except the unstable PbF+ cation).[18] The tetrafluoride, a yellow crystalline powder, is unstable HP Pavilion dv6-1214sl battery. Other dihalides are received upon heating lead(II) salts with the halides of other metals; lead dihalides precipitate to give white orthorhombic crystals (diiodide form yellow hexagonal crystals). They can also be obtained by direct elements reaction at temperature exceeding melting points of dihalides. Their solubility increases with temperature HP Pavilion dv6-1214tx battery; adding more halides first decreases the solubility, but then increases due to complexation, with the maximum coordination number being 6. The complexation depends on halide ion numbers, atomic number of the alkali metal, the halide of which is added, temperature and solution ionic strength.[19] The tetrachloride is obtained upon dissolving the dioxide in hydrochloric acid; to prevent the exothermic decomposition HP Pavilion dv6-1215ax battery, it is kept under concentrated sulfuric acid. The tetrabromide may not, and the tetraiodide definitely does not exist.[20] The diastatide has also been prepared.[21] The metal is not attacked by sulfuric or hydrochloric acids. It dissolves in nitric acid with the evolution of nitric oxide gas to form dissolved Pb(NO3)2.[18] It is a well-soluble solid in water; it is thus a key to receive the precipitates of halide, sulfate, chromate, carbonate, and basic carbonate Pb3(OH)2(CO3)2 salts of lead. HP Pavilion dv6-1215ee batteryOrganolead Main article: Organolead compound The best-known compounds are the two simplest plumbane deratives: tetramethyllead (TML) and tetraethyllead (TEL); however, the homologs of these, as well as hexaethyldilead (HEDL), are of lesser stability. The tetralkyl deratives contain lead(IV); the Pb–C bonds are covalent. They thus resemble typical organic compounds. HP Pavilion dv6-1215ei batteryLead readily forms an equimolar alloy with sodium metal that reacts with alkyl halides to form organometallic compounds of lead such as tetraethyllead.[24] The Pb–C bongs energies in TML and TEL are only 167 and 145 kJ/mol; the compounds thus decompose upon heating, with first signs of TEL composition seen at 100 °C (210 °F) HP Pavilion dv6-1215er battery. The pyrolisis yields of elemental lead and alkyl radicals; their interreaction causes the synthesis of HEDL.[23] They also decompose upon sunlight or UV-light.[25] In presence of chlorine, the alkyls begin to be replaced with chlorides; the R2PbCl2 in the presence of HCl (a by-product of the previous reaction) leads to the complete mineralization to give PbCl2. Reaction with bromine follows the same principle. HP Pavilion dv6-1215ew batteryHistory World lead production peaking in the Roman period and the rising Industrial Revolution[26] Lead ingots from Roman Britain on display at the Wells and Mendip Museum Lead mining in the upper Mississippi River region of the U.S., 1865. Lead has been commonly used for thousands of years because it is widespread, easy to extract and easy to work with. It is highly malleable and ductile as well as easy to smelt. Metallic lead beads dating back to 6400 BCE have been found in Çatalhöyük in modern-day Turkey.[27] In the early Bronze Age, lead was used with antimony and arsenic HP Pavilion dv6-1215ez battery. The largest preindustrial producer of lead was the Roman economy, with an estimated output per annum of 80,000 t, which was typically won as a by-product of extensive silver smelting.[26][28][29] Roman mining activities occurred in Central Europe, Roman Britain, the Balkans, Greece, Asia Minor; Hispania alone accounted for 40% of world production. HP Pavilion dv6-1215sa batteryRoman lead pipes often bore the insignia of Roman emperors (see Roman lead pipe inscriptions). Lead plumbing in the Latin West may have been continued beyond the age of Theoderic the Great into the medieval period.[30] Many Roman "pigs" (ingots) of lead figure in Derbyshire lead mining history and in the history of the industry in other English centers HP Pavilion dv6-1215sd battery. The Romans also used lead in molten form to secure iron pins that held together large limestone blocks in certain monumental buildings. In alchemy, lead was thought to be the oldest metal and was associated with the planet Saturn. Alchemists accordingly used Saturn's symbol (the scythe, ♄) to refer to lead HP Pavilion dv6-1215sf battery. Up to the 17th century, tin was often not differed from lead: lead was called plumbum nigrum (literally, "black plumbum"), while tin was called plumbum candidum (literally, "bright plumbum").[31] Their inherence through history can be seen in other languages: the word "olovo" stands for lead in Czech, but in Russian it ("олово") stands for tin HP Pavilion dv6-1215sg battery. Lead's symbol Pb is an abbreviation of its Latin name plumbum for soft metals; the English words "plumbing", "plumber", "plumb", and "plumb-bob" also derive from this Latin root. Occurrence Lead and zinc bearing carbonate and clastic deposits. Source: USGS Metallic lead does occur in nature, but it is rare. Lead is usually found in ore with zinc, silver and (most abundantly) copper, and is extracted together with these metals. The main lead mineral is galena (PbS), which contains 86.6 % lead by weight. Other common varieties are cerussite (PbCO3) and anglesite (PbSO4) HP Pavilion dv6-1215sl battery. Ore processing Galena, lead ore Most ores contain less than 10% lead, and ores containing as little as 3% lead can be economically exploited. Ores are crushed and concentrated by froth flotation typically to 70% or more. Sulfide ores are roasted, producing primarily lead oxide and a mixture of sulfates and silicates of lead and other metals contained in the ore. HP Pavilion dv6-1215ss batteryLead oxide from the roasting process is reduced in a coke-fired blast furnace.[33] This converts most of the lead to its metallic form. Three additional layers separate in the process and float to the top of the metallic lead. These are slag (silicates containing 1.5% lead), matte (sulfides containing 15% lead), and speiss (arsenides of iron and copper) HP Pavilion dv6-1215tx battery. These wastes contain concentrations of copper, zinc, cadmium, and bismuth that can be recovered economically, as can their content of unreduced lead.[32] Metallic lead that results from the roasting and blast furnace processes still contains significant contaminants of arsenic, antimony, bismuth, zinc, copper, silver, and gold. The melt is treated in a reverberatory furnace with air, steam, and sulfur, which oxidizes the contaminants except silver, gold, and bismuth HP Pavilion dv6-1216ax battery. The oxidized contaminants are removed by drossing, where they float to the top and are skimmed off.[32][34] Most lead ores contain significant concentrations of silver, resulting in the smelted metal also containing silver as a contaminant. Metallic silver as well as gold is removed and recovered economically by means of the Parkes process. HP Pavilion dv6-1216er batteryDesilvered lead is freed of bismuth according to the Betterton-Kroll process by treating it with metallic calcium and magnesium, which forms a bismuth dross that can be skimmed off.[32][34] Very pure lead can be obtained by processing smelted lead electrolytically by means of the Betts process. The process uses anodes of impure lead and cathodes of pure lead in an electrolyte of silica fluoride. HP Pavilion dv6-1216sa batteryProduction and recycling Production and consumption of lead is increasing worldwide. Total annual production is about 8 million tonnes; about half is produced from recycled scrap. The top lead producing countries, as of 2008, are Australia, China, USA, Peru, Canada, Mexico, Sweden, Morocco, South Africa and North Korea.[35] Australia, China and the United States account for more than half of primary production. HP Pavilion dv6-1216sl batteryIn 2010, 9.6 million tonnes of lead were produced, of which 4.1 million tonnes came from mining.[37] At current use rates, the supply of lead is estimated to run out in 42 years.[38] Environmental analyst Lester Brown has suggested lead could run out within 18 years based on an extrapolation of 2% growth per year.[39] This may need to be reviewed to take account of renewed interest in recycling, and rapid progress in fuel cell technology HP Pavilion dv6-1216ss battery. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of lead in use in society is 8 kg. Much of this is in more-developed countries (20–150 kg per capita) rather than less-developed countries (1–4 kg per capita). Applications Elemental form Lead bricks are commonly used as radiation shielding. Because of its high density and resistance from corrosion, lead is used for the ballast keel of sailboats HP Pavilion dv6-1216tx battery. Its high density allows it to counterbalance the heeling effect of wind on the sails while at the same time occupying a small volume and thus offering the least underwater resistance. For the same reason it is used in scuba diving weight belts to counteract the diver's natural buoyancy and that of his equipment. It does not have the weight-to-volume ratio of many heavy metals, but its low cost increases its use in these and other applications HP Pavilion dv6-1217ax battery. Roman lead water pipes with taps Lead pipe in Roman baths Multicolor lead-glazing in a sancai ceramic cup, Tang dynasty, China, 8th century CE. Lead is used in applications where its low melting point, ductility and high density is an advantage. The low melting point makes casting of lead easy, and therefore small arms ammunition and shotgun pellets can be cast with minimal technical equipment HP Pavilion dv6-1217er battery. It is also inexpensive and denser than other common metals.[40] The hot metal typesetting uses a lead based alloy to produce the types for printing directly before printing. Its corrosion resistance makes it suitable for outdoor applications when in contact with water. More than half of the worldwide lead production (at least 1.15 million metric tons) is used for automobiles, mostly as electrodes in the lead–acid battery, used extensively as a car battery. HP Pavilion dv6-1217ss batteryCathode (reduction) PbO2 + 4 H+ + SO42– + 2e– → PbSO4 + 2 H2O Anode (oxidation) Pb + SO42– → PbSO4 + 2e–[42][43] Lead is used as electrodes in the process of electrolysis. Lead is used in solder for electronics, although this usage is being phased out by some countries to reduce the amount of environmentally hazardous waste. Lead is used in high voltage power cables as sheathing material to prevent water diffusion into insulation HP Pavilion dv6-1217tx battery. Lead is one of three metals used in the Oddy test for museum materials, helping detect organic acids, aldehydes, and acidic gases. Lead is used as shielding from radiation (e.g., in X-ray rooms).[44] Molten lead is used as a coolant (e.g., for lead cooled fast reactors).[45] Lead is added to brass to reduce machine tool wear. Lead, in the form of strips, or tape, is used for the customization of tennis rackets. Tennis rackets of the past sometimes had lead added to them by the manufacturer to increase weight. HP Pavilion dv6-1218ca batteryLead is used to form glazing bars for stained glass or other multi-lit windows. The practice has become less common, not for danger but for stylistic reasons. Lead, or sheet-lead, is used as a sound deadening layer in some areas in wall, floor and ceiling design in sound studios where levels of airborne and mechanically produced sound are targeted for reduction or virtual elimination. HP Pavilion dv6-1218ss batteryLead is the traditional base metal of organ pipes, mixed with varying amounts of tin to control the tone of the pipe.[49][50] Lead has many uses in the construction industry (e.g., lead sheets are used as architectural metals in roofing material, cladding, flashing, gutters and gutter joints, and on roof parapets). Detailed lead moldings are used as decorative motifs used to fix lead sheet. Lead is still widely used in statues and sculptures HP Pavilion dv6-1218tx battery. Lead is often used to balance the wheels of a car; this use is being phased out in favor of other materials for environmental reasons. Due to its half-life of 22.2 years, the radioactive isotope 210Pb is used for dating material from marine sediment cores byradiometric methods.[citation needed] Compounds Lead compounds are used as a coloring element in ceramic glazes, notably in the colors red and yellow.[51] Lead is frequently used in polyvinyl chloride (PVC) plastic, which coats electrical cords. HP Pavilion dv6-1219ez batteryLead is used in some candles to treat the wick to ensure a longer, more even burn. Because of the dangers, European and North American manufacturers use more expensive alternatives such as zinc.[54][55] Lead glass is composed of 12–28% lead oxide. It changes the optical characteristics of the glass and reduces the transmission of radiation. HP Pavilion dv6-1219tx batterySome artists using oil-based paints continue to use lead carbonate white, citing its properties in comparison with the alternatives. Tetra-ethyl lead is used as an anti-knock additive for aviation fuel in piston-driven aircraft. Lead-based semiconductors, such as lead telluride, lead selenide and lead antimonide are finding applications in photovoltaic (solar energy) cells and infrared detectors. HP Pavilion dv6-1220ec batteryFormer applications Lead pigments were used in lead paint for white as well as yellow, orange, and red. Most uses have been discontinued due of the dangers of lead poisoning. Beginning April 22, 2010, US federal law requires that contractors performing renovation, repair, and painting projects that disturb more than six square feet of paint in homes HP Pavilion dv6-1220eg battery, child care facilities, and schools built before 1978 must be certified and trained to follow specific work practices to prevent lead contamination. Lead chromate is still in industrial use. Lead carbonate (white) is the traditional pigment for the priming medium for oil painting, but it has been largely displaced by the zinc and titanium oxide pigments HP Pavilion dv6-1220ei battery. It was also quickly replaced in water-based painting mediums. Lead carbonate white was used by the Japanese geisha and in the West for face-whitening make-up, which was detrimental to health.[58][59][60] Lead is the hot metal that was used in hot metal typesetting. It was used for plumbing as well as a preservative for food and drink in Ancient Rome. Until the early 1970s, lead was used for joining cast iron water pipes and used as a material for small diameter water pipes. HP Pavilion dv6-1220ek batteryTetraethyllead was used in leaded fuels to reduce engine knocking, but this practice has been phased out across many countries of the world in efforts to reduce toxic pollution that affected humans and the environment. Lead was used to make bullets for slings. Lead was used for shotgun pellets in the US until about 1992 when it was outlawed (for waterfowl hunting only) and replaced by non-toxic shot, primarily steel pellets HP Pavilion dv6-1220er battery. In the Netherlands, the use of lead shot for hunting and sport shooting was banned in 1993, which caused a large drop in lead emission, from 230 ton in 1990 to 47.5 ton in 1995, two years after the ban.[66] Lead was a component of the paint used on children's toys – now restricted in the United States and across Europe (ROHS Directive). Lead was used in car body filler, which was used in many custom cars in the 1940s–60s HP Pavilion dv6-1220ev battery. Hence the term Leadsled. Lead is a superconductor at 7.2 K and IBM tried to make a Josephson effect computer out of lead-alloy.[67] Lead was also used in pesticides before the 1950s, when fruit orchards were treated (ATSDR). A lead cylinder attached to a long line was used by sailors for the vital navigational task of determining water depth by heaving the lead at regular internals HP Pavilion dv6-1220ew battery. A soft tallow insert at its base allowed the nature of the sea bed to be determined, further aiding position finding. Contrary to popular belief, pencil leads in wooden pencils have never been made from lead. The term comes from the Roman stylus, called the penicillus, which was made of lead without a wooden holder HP Pavilion dv6-1220ez battery.[68] When the pencil originated as a wrapped graphite writing tool, the particular type of graphite being used was named plumbago (lit. act for lead, or lead mockup). Health effects Main article: Lead poisoning Lead is highly poisonous metal (regardless if inhaled or swallowed), affecting almost every organ and system in the body. The main target for lead toxicity is the nervous system, both in adults and children HP Pavilion dv6-1220sa battery. Long-term exposure of adults can result in decreased performance in some tests that measure functions of the nervous system. Long-term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO2) can cause nephropathy, and colic-like abdominal pains. It may also cause weakness in fingers, wrists, or ankles. Lead exposure also causes small increases in blood pressure HP Pavilion dv6-1220sb battery, particularly in middle-aged and older people and can cause anemia. Exposure to high lead levels can severely damage the brain and kidneys in adults or children and ultimately cause death. In pregnant women, high levels of exposure to lead may cause miscarriage. Chronic, high-level exposure have shown to reduce fertility in males HP Pavilion dv6-1220sd battery.[69] Lead also damages nervous connections (especially in young children) and cause blood and brain disorders. Lead poisoning typically results from ingestion of food or water contaminated with lead; but may also occur after accidental ingestion of contaminated soil, dust, or lead-based paint.[70] It is rapidly absorbed into the bloodstream and is believed to have adverse effects on the central nervous system HP Pavilion dv6-1220sh battery, the cardiovascular system, kidneys, and the immune system.[71] The component limit of lead (1.0 μg/g) is a test benchmark for pharmaceuticals, representing the maximum daily intake an individual should have. However, even at this low level, a prolonged intake can be hazardous to human beings.[72][73] The treatment for lead poisoning consists of dimercaprol and succimer. HP Pavilion dv6-1220so batteryNFPA 704 130 Fire diamond for lead granules The concern about lead's role in cognitive deficits in children has brought about widespread reduction in its use (lead exposure has been linked to learning disabilities).[75] Most cases of adult elevated blood lead levels are workplace-related.[76] High blood levels are associated with delayed puberty in girls. HP Pavilion dv6-1220sp battery Lead has been shown many times to permanently reduce the cognitive capacity of children at extremely low levels of exposure.[78] During the 20th century, the use of lead in paint pigments was sharply reduced because of the danger of lead poisoning, especially to children.[79][80] By the mid-1980s, a significant shift in lead end-use patterns had taken place HP Pavilion dv6-1220ss battery. Much of this shift was a result of the U.S. lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in non-battery products, including gasoline, paints, solders, and water systems. Lead use is being further curtailed by the European Union's RoHS directive. Lead may still be found in harmful quantities in stoneware HP Pavilion dv6-1220st battery, vinyl (such as that used for tubing and the insulation of electrical cords), and Chinese brass. Older houses may still contain substantial amounts of lead paint. White lead paint has been withdrawn from sale in industrialized countries, but the yellow lead chromate is still in use. Old paint should not be stripped by sanding, as this produces inhalable dust HP Pavilion dv6-1220tx battery. Lead salts used in pottery glazes have on occasion caused poisoning, when acidic drinks, such as fruit juices, have leached lead ions out of the glaze.[81] It has been suggested that what was known as "Devon colic" arose from the use of lead-lined presses to extract apple juice in the manufacture of cider HP Pavilion dv6-1221ax battery. Lead is considered to be particularly harmful for women's ability to reproduce. Lead(II) acetate (also known as sugar of lead) was used by the Roman Empire as a sweetener for wine, and some consider this to be the cause of the dementia that affected many of the Roman Emperors and even be a partial reason for the Roman Empire's fall (see Decline of the Roman Empire#Lead poisoning). HP Pavilion dv6-1221eo batteryBiochemistry of poisoning In the human body, lead inhibits porphobilinogen synthase and ferrochelatase, preventing both porphobilinogen formation and the incorporation of iron into protoporphyrin IX, the final step in heme synthesis. This causes ineffective heme synthesis and subsequent microcytic anemia.[83] At lower levels, it acts as a calcium analog, interfering with ion channels during nerve conduction. This is one of the mechanisms by which it interferes with cognition HP Pavilion dv6-1221sl battery. Acute lead poisoning is treated using disodium calcium edetate: the calcium chelate of the disodium salt of ethylene-diamine-tetracetic acid (EDTA). This chelating agent has a greater affinity for lead than for calcium and so the lead chelate is formed by exchange. This is then excreted in the urine leaving behind harmless calcium. HP Pavilion dv6-1221tx batteryExposure to lead and lead chemicals can occur through inhalation, ingestion and dermal contact. Most exposure occurs through ingestion or inhalation; in the U.S. the skin exposure is unlikely as leaded gasoline additives are no longer used. Lead exposure is a global issue as lead mining and lead smelting are common in many countries. Most countries have stopped using lead-containing gasoline by 2007. HP Pavilion dv6-1222eo batteryLead exposure mostly occurs through ingestion. Lead paint is the major source of lead exposure for children. As lead paint deteriorates, it peels, is pulverized into dust and then enters the body through hand-to-mouth contact or through contaminated food, water or alcohol. Ingesting certain home remedy medicines may also expose people to lead or lead compounds. HP Pavilion dv6-1222et battery Lead can be ingested through fruits and vegetables contaminated by high levels of lead in the soils they were grown in. Soil is contaminated through particulate accumulation from lead in pipes, lead paint and residual emissions from leaded gasoline that was used before the Environment Protection Agency issue the regulation around 1980. HP Pavilion dv6-1222sl batteryInhalation is the second major pathway of exposure, especially for workers in lead-related occupations. Almost all inhaled lead is absorbed into the body, the rate is 20–70% for ingested lead; children absorb more than adults.[85] Dermal exposure may be significant for a narrow category of people working with organic lead compounds, but is of little concern for general population. The rate of skin absorption is also low for inorganic lead. HP Pavilion dv6-1222tx batteryAccording to Agency for Toxic Substance and Disease Registry, a small amount of lead (1%) will store itself in bones and the rest will be excreted through urine and feces within a few weeks of exposure. Children have a harder time excreting lead. Only about 32% of lead will be excreted by a child. HP Pavilion dv6-1223eo battery
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state (water vapor or steam). Water also exists in a liquid crystal state near hydrophilic surfaces. Sony VAIO VGN-CS33H battery Under nomenclature used to name chemical compounds, dihydrogen monoxide is the scientific name for water, though it is almost never used.[3] Water covers 70.9% of the Earth's surface,[4] and is vital for all known forms of life.[5] On Earth, 96.5% of the planet's water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor, clouds Sony VAIO VGN-CS33H/Z battery (formed of solid and liquid water particles suspended in air), and precipitation.[6][7] Only 2.5% of the Earth's water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products Sony VAIO VGN-CS33H/B battery.[6] Water on Earth moves continually through the hydrological cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land. Safe drinking water is essential to humans and other lifeforms. Access to safe drinking water has improved over the last decades in almost every part of the world Sony VAIO VGN-CS31Z/Q battery, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation.[8] There is a clear correlation between access to safe water and GDP per capita.[9] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.[10] A recent report (November 2009) suggests that by 2030 Sony VAIO VGN-CS31S/W battery, in some developing regions of the world, water demand will exceed supply by 50%.[11] Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture.[12] Chemical and physical properties Main articles: Water (properties), Water (data page), and Water model Model of hydrogen bonds (1) between molecules of water Sony VAIO VGN-CS31S/V batteryImpact from a water drop causes an upward "rebound" jet surrounded by circular capillary waves. Snowflakes by Wilson Bentley, 1902 Dew drops adhering to a spider web Capillary action of water compared to mercury Water is the chemical substance with chemical formula H2O: one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom. Water appears in nature in all three common states of matter and may take many different forms on Earth: water vapor and clouds in the sky; seawater in the oceans; icebergs in the polar oceans; glaciers and rivers in the mountains; and the liquid in aquifers in the ground Sony VAIO VGN-CS31S/T battery. At high temperatures and pressures, such as in the interior of giant planets, it is argued that water exists as ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and at even higher pressures as superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice Sony VAIO VGN-CS31S/R battery.[13] The major chemical and physical properties of water are: Water is a liquid at standard temperature and pressure. It is tasteless and odorless. The intrinsic colour of water and ice is a very slight blue hue, although both appear colorless in small quantities. Water vapour is essentially invisible as a gas.[14] Water is transparent in the visible electromagnetic spectrum. Thus aquatic plants can live in water because sunlight can reach them. Infrared light is strongly absorbed by the hydrogen-oxygen or OH bonds Sony VAIO VGN-CS31S/P battery. Since the water molecule is not linear and the oxygen atom has a higher electronegativity than hydrogen atoms, it carries a slight negative charge, whereas the hydrogen atoms are slightly positive. As a result, water is a polar molecule with an electrical dipole moment. Water also can form an unusually large number of intermolecular hydrogen bonds (four) for a molecule of its size Sony VAIO VGN-CS28 battery. These factors lead to strong attractive forces between molecules of water, giving rise to water's high surface tension[15] and capillary forces. The capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees Sony VAIO VGN-CS28/Q battery.[16] Water is a good solvent and is often referred to as the universal solvent. Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and some gases – especially oxygen, carbon dioxide (carbonation) are known as hydrophilic (water-loving) substances, while those that do not mix well with water (e.g., fats and oils), are known as hydrophobic (water-fearing) substances Sony VAIO VGN-CS27 battery. All the major components in cells (proteins, DNA and polysaccharides) are also dissolved in water. Pure water has a low electrical conductivity, but this increases significantly with the dissolution of a small amount of ionic material such as sodium chloride. The boiling point of water (and all other liquids) is dependent on the barometric pressure. For example, on the top of Mt. Everest water boils at 68 °C (154 °F) Sony VAIO VGN-CS27/W battery, compared to 100 °C (212 °F) at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid. At 4181.3 J/(kg·K), water has a high specific heat capacity, as well as a high heat of vaporization (40.65 kJ·mol−1), both of which are a result of the extensive hydrogen bonding between its molecules Sony VAIO VGN-CS27/R battery. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature. The maximum density of water occurs at 3.98 °C (39.16 °F).[17] It has the anomalous property of becoming less dense, not more, when it is cooled down to its solid form, ice. It expands to occupy 9% greater volume in this solid state, which accounts for the fact of ice floating on liquid water, as in icebergs Sony VAIO VGN-CS27/P battery. Its density is 1,000 kg/m3 (62.428 lb/cu ft or 8.3454 lb/US gal) liquid (at 4 °C; ice has a density of 917 kg/m3).[18] ADR label for transporting goods dangerously reactive with water Water is miscible with many liquids, such as ethanol, in all proportions, forming a single homogeneous liquid. On the other hand, water and most oils are immiscible, usually forming layers according to increasing density from the top. As a gas, water vapor is completely miscible with air Sony VAIO VGN-CS27/C battery. Water forms an azeotrope with many other solvents. Water can be split by electrolysis into hydrogen and oxygen. As an oxide of hydrogen, water is formed when hydrogen or hydrogen-containing compounds burn or react with oxygen or oxygen-containing compounds. Water is not a fuel, it is an end-product of the combustion of hydrogen. The energy required to split water into hydrogen and oxygen by electrolysis or any other means is greater than the energy that can be collected when the hydrogen and oxygen recombine Sony VAIO VGN-CS26T/W battery.[19] Elements which are more electropositive than hydrogen such as lithium, sodium, calcium, potassium and caesium displace hydrogen from water, forming hydroxides. Being a flammable gas, the hydrogen given off is dangerous and the reaction of water with the more electropositive of these elements may be violently explosive Sony VAIO VGN-CS26T/V battery. Taste and odor Water can dissolve many different substances, giving it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water by avoiding water that is too salty or putrid. The taste of spring water and mineral water, often advertised in marketing of consumer products, derives from the minerals dissolved in it Sony VAIO VGN-CS26T/T battery. However, pure H2O is tasteless and odorless. The advertised purity of spring and mineral water refers to absence of toxins, pollutants and microbes, not the absence of naturally occurring minerals. Distribution in nature In the universe Much of the universe's water is produced as a byproduct of star formation. When stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas Sony VAIO VGN-CS26T/R battery, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.[20] On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor, containing "140 trillion times more water than all of Earth's oceans combined," around a quasar located 12 billion light years from Earth. According to the researchers, the "discovery shows that water has been prevalent in the universe for nearly its entire existence." Sony VAIO VGN-CS26T/Q batteryWater has been detected in interstellar clouds within our galaxy, the Milky Way. Water probably exists in abundance in other galaxies, too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe. Interstellar clouds eventually condense into solar nebulae and solar systems such as ours Sony VAIO VGN-CS26T/P battery. Water vapor is present in Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's exosphere[23] Atmosphere of Venus: 0.002% Earth's atmosphere: ~0.40% over full atmosphere, typically 1–4% at surface Atmosphere of Mars: 0.03% Atmosphere of Jupiter: 0.0004% Atmosphere of Saturn – in ices only Enceladus (moon of Saturn): 91% exoplanets known as HD 189733 b[24] and HD 209458 b.[25] Liquid water is present on Earth: 71% of surface Europa: 100 km deep subsurface ocean Strong evidence suggests that liquid water is present just under the surface of Saturn's moon Enceladus Sony VAIO VGN-CS26T/C battery. Water ice is present on Earth – mainly as ice sheets polar ice caps on Mars Moon Titan Europa Saturn's rings[26] Enceladus Pluto and Charon[26] Comets and comet source populations (Kuiper belt and Oort cloud objects). Water ice may be present on Ceres and Tethys. Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune and the water in the deeper layers may be in the form of ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper down as superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice Sony VAIO VGN-CS25H battery.[13] Some of the Moon's minerals contain water molecules. For instance, in 2008 a laboratory device which ejects and identifies particles found small amounts of the compound in the inside of volcanic rock brought from Moon to Earth by the Apollo 15 crew in 1971.[27] NASA reported the detection of water molecules by NASA's Moon Mineralogy Mapper aboard the Indian Space Research Organization's Chandrayaan-1 spacecraft in September 2009 Sony VAIO VGN-CS25H/W battery.[28] Water and habitable zone The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth are vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the solar system; if it were slightly closer to or farther from the Sun (about 5%, or about 8 million kilometers), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Sony VAIO VGN-CS25H/R batteryEarth's gravity allows it to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (greenhouse effect) which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would allow temperature extremes, thus preventing the accumulation of water except in polar ice caps (as on Mars) Sony VAIO VGN-CS25H/Q battery. The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis Sony VAIO VGN-CS25H/P battery. The state of water on a planet depends on ambient pressure, which is determined by the planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity, as it was observed on exoplanets Gliese 436 b[31] and GJ 1214 b Sony VAIO VGN-CS25H/C battery.[32] There are various theories about origin of water on Earth. On Earth Main articles: Hydrology and Water distribution on Earth A graphical distribution of the locations of water on Earth. Water covers 71% of the Earth's surface; the oceans contain 96.5% of the Earth's water. The Antarctic ice sheet, which contains 61% of all fresh water on Earth, is visible at the bottom. Condensed atmospheric water can be seen as clouds, contributing to the Earth's albedo Sony VAIO VGN-CS23T/W battery. Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in focus of ecohydrology Sony VAIO VGN-CS23T/Q battery. The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1,338,000,000 km3 (321,000,000 mi3).[6] Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is sea water. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers Sony VAIO VGN-CS23H battery. Water is important in many geological processes. Groundwater is present in most rocks, and the pressure of this groundwater affects patterns of faulting. Water in the mantle is responsible for the melt that produces volcanoes at subduction zones. On the surface of the Earth, water is important in both chemical and physical weathering processes Sony VAIO VGN-CS23H/S battery. Water and, to a lesser but still significant extent, ice, are also responsible for a large amount of sediment transport that occurs on the surface of the earth. Deposition of transported sediment forms many types of sedimentary rocks, which make up the geologic record of Earth history Sony VAIO VGN-CS23H/B battery. Water cycle Main article: Water cycle Water cycle The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants. Water moves perpetually through each of these regions in the water cycle consisting of following transfer processes Sony VAIO VGN-CS23G battery: evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into air. precipitation, from water vapor condensing from the air and falling to earth or ocean. runoff from the land usually reaching the sea. Most water vapor over the oceans returns to the oceans, but winds carry water vapor over land at the same rate as runoff into the sea, about 47 Tt per year. Over land, evaporation and transpiration contribute another 72 Tt per year Sony VAIO VGN-CS23G/W battery. Precipitation, at a rate of 119 Tt per year over land, has several forms: most commonly rain, snow, and hail, with some contribution from fog and dew.[33] Condensed water in the air may also refract sunlight to produce rainbows. Water runoff often collects over watersheds flowing into rivers. A mathematical model used to simulate river or stream flow and calculate water quality parameters is hydrological transport model. Some of water is diverted to irrigation for agriculture Sony VAIO VGN-CS23G/Q battery. Rivers and seas offer opportunity for travel and commerce. Through erosion, runoff shapes the environment creating river valleys and deltas which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water. It is when a river overflows its banks or flood from the sea Sony VAIO VGN-CS23G/P battery. A drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation. Fresh water storage The Bay of Fundy at high tide (left) and low tide (right) Main article: Water resources Some runoff water is trapped for periods of time, for example in lakes. At high altitude, during winter, and in the far north and south, snow collects in ice caps, snow pack and glaciers. Water also infiltrates the ground and goes into aquifers Sony VAIO VGN-CS21Z/Q battery. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. This water storage is important, since clean, fresh water is essential to human and other land-based life. In many parts of the world, it is in short supply Sony VAIO VGN-CS21S/W battery. Sea water Sea water contains about 3.5% salt on average, plus smaller amounts of other substances. The physical properties of sea water differ from fresh water in some important respects. It freezes at a lower temperature (about −1.9 °C) and its density increases with decreasing temperature to the freezing point, instead of reaching maximum density at a temperature above freezing Sony VAIO VGN-CS21S/V battery. The salinity of water in major seas varies from about 0.7% in the Baltic Sea to 4.0% in the Red Sea. Tides Tides are the cyclic rising and falling of local sea levels caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams Sony VAIO VGN-CS21S/T battery. The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local bathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides Sony VAIO VGN-CS21S/R battery. Effects on life An oasis is an isolated water source with vegetation in a desert Overview of photosynthesis and respiration. Water (at right), together with carbon dioxide (CO2), form oxygen and organic compounds (at left), which can be respired to water and (CO2). From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances Sony VAIO VGN-CS21S/P battery. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism Sony VAIO VGN-CS215J/R battery. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g. starches, triglycerides and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g. glucose, fatty acids and amino acids to be used for fuels for energy use or other purposes) Sony VAIO VGN-CS215J/Q battery. Without water, these particular metabolic processes could not exist. Water is fundamental to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO2 in the process (cellular respiration) Sony VAIO VGN-CS19/W battery. Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as hydroxide ion (OH−) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7 Sony VAIO VGN-CS19/R battery. Some of the biodiversity of a coral reef Aquatic life forms Main articles: Hydrobiology and Aquatic plant Some marine diatoms – a key phytoplankton group Earth surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land Sony VAIO VGN-CS19/Q battery. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain. Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breathe air Sony VAIO VGN-CS19/P battery. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see insect and mollusc siphons) and gills (Carcinus). However as invertebrate life evolved in an aquatic habitat most have little or no specialisation for respiration in water Sony VAIO VGN-CS17H/W battery. Effects on human civilization Water fountain Civilization has historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Buenos Aires, Shanghai Sony VAIO VGN-CS17H/Q battery, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development Sony VAIO VGN-CS16T/W battery. Health and pollution Environmental Science Program, Iowa State University student sampling water. Water fit for human consumption is called drinking water or potable water. Water that is not potable may be made potable by filtration or distillation, or by a range of other methods. Water that is not fit for drinking but is not harmful for humans when used for swimming or bathing is called by various names other than potable or drinking water Sony VAIO VGN-CS16T/T battery, and is sometimes called safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1–2 ppm of chlorine not yet reacted with impurities for bathing water) Sony VAIO VGN-CS16T/R battery. Water for bathing may be maintained in satisfactory microbiological condition using chemical disinfectants such as chlorine or ozone or by the use of ultraviolet light. In the USA, non-potable forms of wastewater generated by humans may be referred to as greywater, which is treatable and thus easily able to be made potable again, and blackwater, which generally contains sewage and other forms of waste which require further treatment in order to be made reusable Sony VAIO VGN-CS16T/Q battery. Greywater composes 50–80% of residential wastewater generated by a household's sanitation equipment (sinks, showers and kitchen runoff, but not toilets, which generate blackwater.) These terms may have different meanings in other countries and cultures. This natural resource is becoming scarcer in certain places, and its availability is a major social and economic concern Sony VAIO VGN-CS16T/P battery. Currently, about a billion people around the world routinely drink unhealthy water. Most countries accepted the goal of halving by 2015 the number of people worldwide who do not have access to safe water and sanitation during the 2003 G8 Evian summit.[34] Even if this difficult goal is met, it will still leave more than an estimated half a billion people without access to safe drinking water and over a billion without access to adequate sanitation Sony VAIO VGN-CS13T/W battery. Poor water quality and bad sanitation are deadly; some five million deaths a year are caused by polluted drinking water. The World Health Organization estimates that safe water could prevent 1.4 million child deaths from diarrhea each year.[35] Water, however, is not a finite resource, but rather re-circulated as potable water in precipitation in quantities many degrees of magnitude higher than human consumption Sony VAIO VGN-CS13H/W battery. Therefore, it is the relatively small quantity of water in reserve in the earth (about 1% of our drinking water supply, which is replenished in aquifers around every 1 to 10 years), that is a non-renewable resource, and it is, rather, the distribution of potable and irrigation water which is scarce, rather than the actual amount of it that exists on the earth Sony VAIO VGN-CS13H/R battery. Water-poor countries use importation of goods as the primary method of importing water (to leave enough for local human consumption), since the manufacturing process uses around 10 to 100 times products' masses in water. In the developing world, 90% of all wastewater still goes untreated into local rivers and streams. Sony VAIO VGN-CS13H/Q battery Some 50 countries, with roughly a third of the world’s population, also suffer from medium or high water stress, and 17 of these extract more water annually than is recharged through their natural water cycles.[37] The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources Sony VAIO VGN-CS13H/P battery. Human uses Further information: Water supply Agriculture Irrigation of field crops The most important use of water in agriculture is for irrigation, which is a key component to produce enough food. Irrigation takes up to 90% of water withdrawn in some developing countries[38] and significant proportions in more economically developed countries (United States, 30% of freshwater usage is for irrigation) Sony VAIO VGN-CS11Z/T battery.[39] It takes around 3,000 litres of water, converted from liquid to vapour, to produce enough food to satisfy one person's daily dietary need. This is a considerable amount, when compared to that required for drinking, which is between two and five litres. To produce food for the 6.5 billion or so people who inhabit the planet today requires the water that would fill a canal ten metres deep Sony VAIO VGN-CS11Z/R battery, 100 metres wide and 7.1 million kilometres long – that's enough to circle the globe 180 times. Fifty years ago, the common perception was that water was an infinite resource. At this time, there were fewer than half the current number of people on the planet. People were not as wealthy as today, consumed fewer calories and ate less meat, so less water was needed to produce their food Sony VAIO VGN-CS11S/W battery. They required a third of the volume of water we presently take from rivers. Today, the competition for the fixed amount of water resources is much more intense, giving rise to the concept of peak water.[40] This is because there are now nearly seven billion people on the planet, their consumption of water-thirsty meat and vegetables is rising, and there is increasing competition for water from industry Sony VAIO VGN-CS11S/Q battery, urbanisation and biofuel crops. In future, even more water will be needed to produce food because the Earth's population is forecast to rise to 9 billion by 2050.[41] An additional 2.5 or 3 billion people, choosing to eat fewer cereals and more meat and vegetables could add an additional five million kilometres to the virtual canal mentioned above Sony VAIO VGN-CS11S/P battery. An assessment of water management in agriculture was conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population.[42] It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity (Sony VAIO VGN-AW11M/H battery). It found that a fifth of the world's people, more than 1.2 billion, live in areas of physical water scarcity, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencing economic water scarcity, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water (Sony VAIO VGN-AW11S/B battery). The report found that it would be possible to produce the food required in future, but that continuation of today's food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industry and cities find ways to use water more efficiently (Sony VAIO VGN-AW11Z/B battery).[43] As a scientific standard On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one hundredth of a meter, and to the temperature of the melting ice."[44] For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram (Sony VAIO VGN-AW170C battery). Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C — a highly reproducible temperature — the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F). (Sony VAIO VGN-AW19/Q battery)The Kelvin temperature scale of the SI system is based on the triple point of water, defined as exactly 273.16 K or 0.01 °C. The scale is an absolute temperature scale with the same increment as the Celsius temperature scale, which was originally defined according the boiling point (set to 100 °C) and melting point (set to 0 °C) of water (Sony VAIO VGN-AW19 battery). Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also small quantity of heavier isotopes such as hydrogen-2 (deuterium). The amount of deuterium oxides or heavy water is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less deuterium than seawater. Therefore, standard water is defined in the Vienna Standard Mean Ocean Water specification (Sony VAIO VGN-AW21M/H battery). For drinking Main article: Drinking water A young girl drinking bottled water Water quality: fraction of population using improved water sources by country The human body contains from 55% to 78% water, depending on body size.[46] To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water (Sony VAIO VGN-AW21S/B battery). It is not clear how much water intake is needed by healthy people, though most advocates agree that approximately 2 liters (6 to 7 glasses) of water daily is the minimum to maintain proper hydration.[47] Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather (Sony VAIO VGN-AW21VY/Q battery).[48] For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is dangerous to drink too little. People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication (hyperhydration), which can be fatal. (Sony VAIO VGN-AW21XY/Q battery) The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science.[51] Similar misconceptions concerning the effect of water on weight loss and constipation have also been dispelled.[52] Hazard symbol for non-potable water An original recommendation for water intake in 1945 by the Food and Nutrition Board of the United States National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food (Sony VAIO VGN-AW21Z/B battery). Most of this quantity is contained in prepared foods."[53] The latest dietary reference intake report by the United States National Research Council in general recommended (including food sources): 3.7 liters for men and 2.7 liters of water total for women.[54] Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The Institute of Medicine (U.S.) recommends that (Sony VAIO VGN-AW230J/H battery), on average, men consume 3.0 liters and women 2.2 liters; pregnant women should increase intake to 2.4 liters (10 cups) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing.[55] Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included) (Sony VAIO VGN-AW235J/B battery). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well. Humans require water with few impurities. Common impurities include metal salts and oxides, including copper, iron, calcium and lead,[56] and/or harmful bacteria (Sony VAIO VGN-AW31M/H battery), such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.[57] The single largest (by volume) freshwater resource suitable for drinking is Lake Baikal in Siberia.[58] Washing The propensity of water to form solutions and emulsions is useful in various washing processes. Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water slurries or using water to dissolve and extract substances. Washing is also an important component of several aspects of personal body hygiene (Sony VAIO VGN-AW31S/B battery). Transportation The use of water for transportation of materials through rivers and canals as well as the international shipping lanes is an important part of the world economy. Chemical uses Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds. In organic reactions, it is not usually used as a reaction solvent (Sony VAIO VGN-AW31XY/Q battery), because it does not dissolve the reactants well and is amphoteric (acidic and basic) and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently( SONY Vaio VGN-NS38M Battery). Heat exchange Water and steam are used as heat transfer fluids in diverse heat exchange systems, due to its availability and high heat capacity, both as a coolant and for heating. Cool water may even be naturally available from a lake or the sea. Condensing steam is a particularly efficient heating fluid because of the large heat of vaporization( SONY Vaio VGN-NS31S Battery). A disadvantage is that water and steam are somewhat corrosive. In almost all electric power stations, water is the coolant, which vaporizes and drives steam turbines to drive generators. In the U.S., cooling power plants is the largest use of water.[39] In the nuclear power industry, water can also be used as a neutron moderator. In most nuclear reactors, water is both a coolant and a moderator( SONY Vaio VGN-NS31M Battery). This provides something of a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down – however other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling. Fire extinction( SONY Vaio VGN-NS31Z Battery) Water is used for fighting wildfires. Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents, because many organic materials float on water and the water tends to spread the burning liquid( SONY Vaio VGN-NS21Z Battery). Use of water in fire fighting should also take into account the hazards of a steam explosion, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal, charcoal, coke graphite, decompose the water, producing water gas( SONY Vaio VGN-NS21M Battery). The power of such explosions was seen in the Chernobyl disaster, although the water involved did not come from fire-fighting at that time but the reactor's own water cooling system. A steam explosion occurred when the extreme overheating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of reaction between steam and hot zirconium( SONY Vaio VGN-NS21S Battery). Recreation Grand Anse Beach, St. George's, Grenada, West Indies, often reported as one of the top 10 beaches in the world. Main article: Water sport (recreation) Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, surfing and diving. In addition, some sports, like ice hockey and ice skating, are played on ice( SONY Vaio VGN-NS12S Battery). Lakesides, beaches and water parks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other water features are popular decorations. Some keep fish and other life in aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports i.e. skiing, sledding, snowmobiling or snowboarding, which requires the water to be frozen( SONY Vaio VGN-NS12M Battery). Water industry A water-carrier in India, 1882. In many places where running water is not available, water has to be transported by people. A manual water pump in China Water purification facility The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities include water wells cisterns for rainwater harvesting, water supply network, water purification facilities, water tanks, water towers, water pipes including old aqueducts. Atmospheric water generators are in development( SONY Vaio VGN-NS11Z Battery). Drinking water is often collected at springs, extracted from artificial borings (wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection( SONY Vaio VGN-NS11M Battery). Water may require purification for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis( SONY Vaio VGN-NS11L Battery). Desalination of abundant seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems, tanker delivery or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources( SONY Vaio VGN-NS11J Battery). Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as externalities for which the market cannot account( SONY Vaio VGN-NS11E Battery). Thus other people pay the price of water pollution, while the private firms' profits are not redistributed to the local population victim of this pollution. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable. Wastewater facilities are storm sewers and wastewater treatment plants. Another way to remove pollution from surface runoff water is bioswale( SONY Vaio VGN-NS10L Battery). Industrial applications Water is used in power generation. Hydroelectricity is electricity obtained from hydropower. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source. The energy is supplied by the motion of water. Typically a dam is constructed on a river, creating an artificial lake behind it. Water flowing out of the lake is forced through turbines that turn generators( SONY Vaio VGN-NS10J Battery). Three Gorges Dam is the largest hydro-electric power station. Pressurized water is used in water blasting and water jet cutters. Also, very high pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment. It is also used in the cooling of machinery to prevent overheating, or prevent saw blades from overheating( SONY Vaio VGN-NS10E Battery). Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution) ( SONY Vaio VGN-NS38M/W Battery). Industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge. Food processing Water can be used to cook foods such as noodles. Water plays many critical roles within the field of food science. It is important for a food scientist to understand the roles that water plays within food processing to ensure the success of their products( SONY Vaio VGN-NS38M/P Battery). Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water are affected by solutes, as well as air pressure, which is in turn affected by altitude. Water boils at lower temperatures with the lower air pressure which occurs at higher elevations. One mole of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C( SONY Vaio VGN-NS31Z/W Battery), and one mole of salt per kg raises the boiling point by 1.02 °C; similarly, increasing the number of dissolved particles lowers water's freezing point.[59] Solutes in water also affect water activity which affects many chemical reactions and the growth of microbes in food.[60] Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water. ( SONY Vaio VGN-NS31Z/S Battery) Solutes in water lower water activity. This is important to know because most bacterial growth ceases at low levels of water activity.[60] Not only does microbial growth affect the safety of food but also the preservation and shelf life of food. Water hardness is also a critical factor in food processing. It can dramatically affect the quality of a product as well as playing a role in sanitation. Water hardness is classified based on the amounts of removable calcium carbonate salt it contains per gallon( SONY Vaio VGN-NS31Z/P Battery). Water hardness is measured in grains; 0.064 g calcium carbonate is equivalent to one grain of hardness.[59] Water is classified as soft if it contains 1 to 4 grains, medium if it contains 5 to 10 grains and hard if it contains 11 to 20 grains.[vague] [59] The hardness of water may be altered or treated by using a chemical ion exchange system. The hardness of water also affects its pH balance which plays a critical role in food processing( SONY Vaio VGN-NS31S/S Battery). For example, hard water prevents successful production of clear beverages. Water hardness also affects sanitation; with increasing hardness, there is a loss of effectiveness for its use as a sanitizer.[59] Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam. Water is also used for dishwashing( SONY Vaio VGN-NS31M/W Battery). Water law, water politics and water crisis Water politics is politics affected by water and water resources. For this reason, water is a strategic resource in the globe and an important element in many political conflicts. It causes health impacts and damage to biodiversity. 1.6 billion people have gained access to a safe water source since 1990.[61] The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970[62] to 71% in 1990( SONY Vaio VGN-NS31M/P Battery), 79% in 2000 and 84% in 2004. This trend is projected to continue.[8] To halve, by 2015, the proportion of people without sustainable access to safe drinking water is one of the Millennium Development Goals. This goal is projected to be reached. A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption( SONY Vaio VGN-NS21Z/S Battery).[63] In addition, global initiatives to improve the efficiency of aid delivery, such as the Paris Declaration on Aid Effectiveness, have not been taken up by water sector donors as effectively as they have in education and health, potentially leaving multiple donors working on overlapping projects and recipient governments without empowerment to act( SONY Vaio VGN-NS21S/W Battery).[64] The authors of the 2007 Comprehensive Assessment of Water Management in Agriculture cited poor governance as one reason for some forms of water scarcity. Water governance is the set of formal and informal processes through which decisions related to water management are made. Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context( SONY Vaio VGN-NS21S/S Battery). Mistakes have sometimes been made by trying to apply 'blueprints' that work in the developed world to developing world locations and contexts. The Mekong river is one example; a review by the International Water Management Institute of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost-benefit analyses and environmental impact assessments were rarely undertaken( SONY Vaio VGN-NS21M/W Battery). They also discovered that Cambodia's draft water law was much more complex than it needed to be.[65] The UN World Water Development Report (WWDR, 2003) from the World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%( SONY Vaio VGN-NS21M/P Battery). 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from waterborne diseases (related to the consumption of contaminated water) or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases; often this means lack of sewage disposal; see toilet( SONY Vaio VGN-NS12S/S Battery). Organizations concerned with water protection include International Water Association (IWA), WaterAid, Water 1st, American Water Resources Association. The International Water Management Institute undertakes projects with the aim of using effective water management to reduce poverty. Water related conventions are United Nations Convention to Combat Desertification (UNCCD) ( SONY Vaio VGN-NS12M/W Battery), International Convention for the Prevention of Pollution from Ships, United Nations Convention on the Law of the Sea and Ramsar Convention. World Day for Water takes place on 22 March and World Ocean Day on 8 June. Water used in the production of a good or service is virtual water. In culture Religion Main article: Water and religion Water is considered a purifier in most religions. Major faiths that incorporate ritual washing (ablution) include Christianity, Hinduism, Islam, Judaism, Rastafari movement, Shinto, Taoism, and Wicca( SONY Vaio VGN-NS12M/S Battery). Immersion (or aspersion or affusion) of a person in water is a central sacrament of Christianity (where it is called baptism); it is also a part of the practice of other religions, including Islam (Ghusl), Judaism (mikvah) and Sikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism( SONY Vaio VGN-NS11Z/S Battery). In Islam, the five daily prayers can be done in most cases after completing washing certain parts of the body using clean water (wudu), unless water is unavailable (see Tayammum). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of misogi). Water is mentioned numerous times in the Bible, for example: "The earth was formed out of water and by water" (NIV) ( SONY Vaio VGN-NS11S/S Battery). In the Qur'an it is stated that "Living things are made of water" and it is often used to describe paradise. Philosophy The Ancient Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic substance of the universe. Water was considered cold and moist. In the theory of the four bodily humors, water was associated with phlegm. The classical element of Water was also one of the five elements in traditional Chinese philosophy, along with earth, fire, wood, and metal( SONY Vaio VGN-NS11M/S Battery). Water is also taken as a role model in some parts of traditional and popular Asian philosophy. James Legge's 1891 translation of the Dao De Jing states "The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike( SONY Vaio VGN-NS11L/S Battery). Hence (its way) is near to (that of) the Tao" and "There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it—for there is nothing (so effectual) for which it can be changed."[66] Literature Water is used in literature as a symbol of purification. Examples include the critical importance of a river in As I Lay Dying by William Faulkner and the drowning of Ophelia in Hamlet( SONY Vaio VGN-NS11E/S Battery). Sherlock Holmes held that "From a drop of water, a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other."[67]
Carbon dioxide (chemical formula CO2) is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state, as a trace gas at a concentration of 0.039% by volume HP Pavilion dv6-1299lx battery. As part of the carbon cycle known as photosynthesis, plants, algae, and cyanobacteria absorb carbon dioxide, light, and water to produce carbohydrate energy for themselves and oxygen as a waste product.[1] But in darkness photosynthesis cannot occur, and during the resultant respiration small amounts of carbon dioxide are produced HP Pavilion dv6-1299ez battery.[2] Carbon dioxide is also produced by combustion of coal or hydrocarbons, the fermentation of liquids and the breathing of humans and animals. In addition it is emitted from volcanoes, hot springs, geysers and other places where the earth’s crust is thin; and is freed from carbonate rocks by dissolution. CO2 is also found in lakes at depth under the sea, and commingled with oil and gas deposits HP Pavilion dv6-1299es battery.[3] As of November 2011, carbon dioxide in the Earth's atmosphere is at a concentration of approximately 390 ppm by volume.[4] Atmospheric concentrations of carbon dioxide fluctuate slightly with the change of the seasons, driven primarily by seasonal plant growth in the Northern Hemisphere HP Pavilion dv6-1299er battery. Concentrations of carbon dioxide fall during the northern spring and summer as plants consume the gas, and rise during the northern autumn and winter as plants go dormant, die and decay. Taking all this into account, the concentration of CO2 grew by about 2 ppm in 2009.[5] Carbon dioxide is a greenhouse gas as it transmits visible light but absorbs strongly in the infrared and near-infrared, before slowly re-emitting the infrared at the same wavelength as what was absorbed HP Pavilion dv6-1299eo battery. Before the advent of human-caused release of carbon dioxide to the atmosphere, concentrations tended to increase with increasing global temperatures, acting as a positive feedback for changes induced by other processes such as orbital cycles.[6] There is a seasonal cycle in CO2 concentration associated primarily with the Northern Hemisphere growing season HP Pavilion dv6-1299ef battery.[7] Carbon dioxide has no liquid state at pressures below 5.1 standard atmospheres (520 kPa). At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below −78.5 °C (−109.3 °F; 194.7 K) and the solid sublimes directly to a gas above −78.5 °C. In its solid state, carbon dioxide is commonly called dry ice HP Pavilion dv6-1299ea battery. CO2 dissolves in water forming carbonic acid[8], which is a weak acid, because CO2 molecule ionization in water is incomplete. The hydration equilibrium constant Kh (at 25 °C) of carbonic acid is [H2CO3]/[CO2] = 1.70×10−3: Hence, the majority of the carbon dioxide is not converted into carbonic acid, but remains as CO2 molecules not affecting the pH. It is an amphoteric substance that can act as an acid or as a base, depending on pH of the solution HP Pavilion dv6-1295el battery. CO2 is an asphyxiant gas and not classified as toxic or harmful in accordance with Globally Harmonized System of Classification and Labelling of Chemicals standards of United Nations Economic Commission for Europe by using the OECD Guidelines for the Testing of Chemicals. In higher concentrations 1% (10,000 ppm) will make some people feel drowsy HP Pavilion dv6-1291es battery.[9] Concentrations of 7% to 10% may cause suffocation, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.[10] In organisms carbonic acid production is catalysed by the enzyme, carbonic anhydrase. CO2 + H2O H2CO3 Chemical and physical properties [edit]Structure and bonding The carbon dioxide molecule is linear and centrosymmetric. The two C-O bonds are equivalent and are short (116.3 pm), consistent with double bonding.[11] Since it is centrosymmetric, the molecule has no electrical dipole HP Pavilion dv6-1290ev battery. Consistent with this fact, only two vibrational bands are observed in the IR spectrum – an antisymmetic stretching mode at 2349 cm−1 and a bending mode near 666 cm−1. There is also a symmetric stretching mode at 1388 cm−1 which is only observed in the Raman spectrum. [edit]In aqueous solution Carbon dioxide is soluble in water, in which it reversibly converts to H2CO3 (carbonic acid). The relative concentrations of CO2, H2CO3, and the deprotonated forms HCO− HP Pavilion dv6-1290es battery3 (bicarbonate) and CO2− 3(carbonate) depend on the pH. In neutral or slightly alkaline water (pH > 6.5), the bicarbonate form predominates (>50%) becoming the most prevalent (>95%) at the pH of seawater. In very alkaline water (pH > 10.4), the predominant (>50%) form is carbonate. The oceans, being mildly alkaline with typical pH = 8.2 – 8.5, contain about 120 mg of bicarbonate per liter HP Pavilion dv6-1290en battery. Being diprotic, carbonic acid has two acid dissociation constants, the first one for the dissociation into the bicarbonate (also called hydrogen carbonate) ion (HCO3−): H2CO3 HCO3− + H+ Ka1 = 2.5×10−4 ; pKa1 = 3.6 at 25 °C.[11] At high pH, the bicarbonate ion dissociates significantly into the carbonate ion (CO32−): HCO3− CO32− + H+ Ka2 = 4.69×10−11 ; pKa2 = 10.329 [edit]Chemical reactions of CO2 Overall, CO2 is a weak electrophile. Its reaction with basic water illustrates this property, in which case hydroxide is the nucleophile. Other nucleophiles react as well. For example, carbanions as provided by Grignard reagents and organolithium compounds react with CO2 to give carboxylates HP Pavilion dv6-1290ec battery: MR + CO2 → RCO2M (where M = Li or MgBr and R = alkyl or aryl). In metal carbon dioxide complexes, CO2 serves as a ligand, which can facilitate the conversion of CO2 to other chemicals.[12] The reduction of CO2 to CO is ordinarily a difficult and slow reaction: CO2 + 2 e- + 2H+ → CO + H2O The redox potential for this reaction near pH 7 is about −0.53 V vs NHE. The nickel-containing enzyme carbon monoxide dehydrogenase catalyses this process HP Pavilion dv6-1288la battery.[13] [edit]Physical properties Carbon dioxide pressure-temperature phase diagram showing the triple point and critical point of carbon dioxide Sample of solid carbon dioxide or "dry ice" pellets For more details on this topic, see Carbon dioxide (data page). Carbon dioxide is colorless. At low concentrations, the gas is odorless. At higher concentrations it has a sharp, acidic odor. At standard temperature and pressure, the density of carbon dioxide is around 1.98 kg/m3, about 1.5 times that of air. At atmospheric pressure and a temperature of −78.51 °C (−109.32 °F) HP Pavilion dv6-1285es battery, carbon dioxide changes directly from a solid phase to a gaseous phase through sublimation, or from gaseous to solid through deposition. Liquid carbon dioxide forms only at pressures above 5.1 atm; the triple point of carbon dioxide is about 518 kPa at −56.6 °C (see phase diagram, above). The critical point is 7.38 MPa at 31.1 °C.[14] Another form of solid carbon dioxide observed at high pressure is an amorphous glass-like solid HP Pavilion dv6-1282et battery.[15] This form of glass, called carbonia, is produced by supercooling heated CO2 at extreme pressure (40–48 GPa or about 400,000 atmospheres) in a diamond anvil. This discovery confirmed the theory that carbon dioxide could exist in a glass state similar to other members of its elemental family, like silicon (silica glass) and germanium dioxide. Unlike silica and germania glasses HP Pavilion dv6-1280us battery, however, carbonia glass is not stable at normal pressures and reverts to gas when pressure is released. See also: Supercritical carbon dioxide, dry ice, and MO diagram [edit]History Crystal structure of dry ice Carbon dioxide was one of the first gases to be described as a substance distinct from air. In the seventeenth century, the Flemish chemist Jan Baptist van Helmont observed that when he burned charcoal in a closed vessel, the mass of the resulting ash was much less than that of the original charcoal HP Pavilion dv6-1280sn battery. His interpretation was that the rest of the charcoal had been transmuted into an invisible substance he termed a "gas" or "wild spirit" (spiritus sylvestre). The properties of carbon dioxide were studied more thoroughly in the 1750s by the Scottish physician Joseph Black. He found that limestone (calcium carbonate) could be heated or treated with acids to yield a gas he called "fixed air." He observed that the fixed air was denser than air and supported neither flame nor animal life HP Pavilion dv6-1280ev battery. Black also found that when bubbled through an aqueous solution of lime (calcium hydroxide), it would precipitate calcium carbonate. He used this phenomenon to illustrate that carbon dioxide is produced by animal respiration and microbial fermentation. In 1772, English chemist Joseph Priestley published a paper entitled Impregnating Water with Fixed Air in which he described a process of dripping sulfuric acid (or oil of vitriol as Priestley knew it) HP Pavilion dv6-1280et battery on chalk in order to produce carbon dioxide, and forcing the gas to dissolve by agitating a bowl of water in contact with the gas.[16] This was the invention of Soda water. Carbon dioxide was first liquefied (at elevated pressures) in 1823 by Humphry Davy and Michael Faraday.[17] The earliest description of solid carbon dioxide was given by Charles Thilorier, who in 1834 opened a pressurized container of liquid carbon dioxide, only to find that the cooling produced by the rapid evaporation of the liquid yielded a "snow" of solid CO2 HP Pavilion dv6-1280es battery.[18] [edit]Isolation and production Carbon dioxide is mainly produced as an unrecovered side product of four technologies: combustion of fossil fuels, production of hydrogen by steam reforming, ammonia synthesis, and fermentation. It can be obtained by or from air distillation, however, this method is inefficient. The combustion of all carbon-containing fuels, such as methane (natural gas) HP Pavilion dv6-1280ep battery, petroleum distillates (gasoline, diesel, kerosene, propane), but also of coal and wood, will yield carbon dioxide and, in most cases, water. As an example the chemical reaction between methane and oxygen is given below. CH4+ 2 O2→ CO2+ 2 H2O The production of quicklime (CaO), a compound that enjoys widespread use, involves the heating (calcining) of limestone at about 850 °C: CaCO3→ CaO + CO2 Iron is reduced from its oxides with coke in a blast furnace, producing pig iron and carbon dioxide: HP Pavilion dv6-1280el batteryFe2O3+ 3 CO → 2 Fe + 3 CO2 Yeast metabolizes sugar to produce carbon dioxide and ethanol, also known as alcohol, in the production of wines, beers and other spirits, but also in the production of bioethanol: C6H12O6 → 2 CO2+ 2 C2H5OH All aerobic organisms produce CO2 when they oxidize carbohydrates, fatty acids, and proteins in the mitochondria of cells. The large number of reactions involved are exceedingly complex and not described easily. Refer to (cellular respiration, anaerobic respiration and photosynthesis) HP Pavilion dv6-1277la battery. The equation for the respiration of glucose and other monosachharides is: C6H12O6 + 6 O2 → 6 CO2 + 6 H2O Photoautotrophs (i.e. plants, cyanobacteria) use another modus operandi: Plants absorb CO2 from the air, and, together with water, react it to form carbohydrates: nCO2 + nH2O → (CH2O)n + nO2 [edit]Laboratory methods A variety of chemical routes to carbon dioxide are known, such as the reaction between most acids and most metal carbonates. For example, the reaction between hydrochloric acid and calcium carbonate (limestone or chalk) is depicted below HP Pavilion dv6-1277el battery: 2 HCl+ CaCO3→ CaCl2+ H2CO3 The carbonic acid (H2CO3) then decomposes to water and CO2. Such reactions are accompanied by foaming or bubbling, or both. In industry such reactions are widespread because they can be used to neutralize waste acid streams. [edit]Industrial production Industrial carbon dioxide can be produced by several methods, many of which are practiced at various scales.[20] In its dominant route, carbon dioxide is produced as a side product of the industrial production of ammonia and hydrogen HP Pavilion dv6-1275la battery. These processes begin with the reaction of water and natural gas (mainly methane).[21] Although carbon dioxide is not often recovered, carbon dioxide results from combustion of fossil fuels and wood as well fermentation of sugar in the brewing of beer, whisky and other alcoholic beverages. It also results from thermal decomposition of limestone, CaCO3, in the manufacture of lime (Calcium oxide, CaO) HP Pavilion dv6-1275eg battery. Directly from natural carbon dioxide springs, where it is produced by the action of acidified water on limestone or dolomite. [edit]Uses Carbon dioxide bubbles in a soft drink. Carbon dioxide is used by the food industry, the oil industry, and the chemical industry.[20] [edit]Precursor to chemicals In the chemical industry, carbon dioxide is mainly consumed as an ingredient in the production of urea and methanol. Metal carbonates and bicarbonates, as well as some carboxylic acids derivatives (e.g., sodium salicylate) are prepared from CO2 HP Pavilion dv6-1270st battery. [edit]Foods Carbon dioxide is a food additive used as a propellant and acidity regulator in the food industry. It is approved for usage in the EU[22] (listed as E number E290), USA[23] and Australia and New Zealand[24] (listed by its INS number 290). A candy called Pop Rocks is pressurized with carbon dioxide gas at about 40 bar (580 psi). When placed in the mouth, it dissolves (just like other hard candy) and releases the gas bubbles with an audible pop HP Pavilion dv6-1270ss battery. Leavening agents cause dough to rise by producing carbon dioxide. Baker's yeast produces carbon dioxide by fermentation of sugars within the dough, while chemical leaveners such as baking powder and baking soda release carbon dioxide when heated or if exposed to acids. [edit]Beverages Carbon dioxide is used to produce carbonated soft drinks and soda water. Traditionally, the carbonation in beer and sparkling wine came about through natural fermentation HP Pavilion dv6-1270la battery, but many manufacturers carbonate these drinks with carbon dioxide recovered from the fermentation process. In the case of bottled and kegged beer, recycled carbon dioxide carbonation is the most common method used. With the exception of British Real Ale, draught beer is usually transferred from kegs in a cold room or cellar to dispensing taps on the bar using pressurized carbon dioxide, sometimes mixed with nitrogen HP Pavilion dv6-1270ev battery. [edit]Wine making Carbon dioxide in the form of dry ice is often used in the wine making process to cool down bunches of grapes quickly after picking to help prevent spontaneous fermentation by wild yeasts. The main advantage of using dry ice over regular water ice is that it cools the grapes without adding any additional water that may decrease the sugar concentration in the grape must HP Pavilion dv6-1270et battery, and therefore also decrease the alcohol concentration in the finished wine. Dry ice is also used during the cold soak phase of the wine making process to keep grapes cool. The carbon dioxide gas that results from the sublimation of the dry ice tends to settle to the bottom of tanks because it is heavier than air. The settled carbon dioxide gas creates a hypoxic environment which helps to prevent bacteria from growing on the grapes until it is time to start the fermentation with the desired strain of yeast HP Pavilion dv6-1270eq battery. Carbon dioxide is also used to create a hypoxic environment for carbonic maceration, the process used to produce Beaujolais wine. Carbon dioxide is sometimes used to top up wine bottles or other storage vessels such as barrels to prevent oxidation, though it has the problem that it can dissolve into the wine, making a previously still wine slightly fizzy. For this reason, other gases such as nitrogen or argon are preferred for this process by professional wine makers HP Pavilion dv6-1270el battery. [edit]Inert gas It is one of the most commonly used compressed gases for pneumatic (pressurized gas) systems in portable pressure tools. Carbon dioxide also finds use as an atmosphere for welding, although in the welding arc, it reacts to oxidize most metals. Use in the automotive industry is common despite significant evidence that welds made in carbon dioxide are more brittle than those made in more inert atmospheres HP Pavilion dv6-1270eg battery, and that such weld joints deteriorate over time because of the formation of carbonic acid. It is used as a welding gas primarily because it is much less expensive than more inert gases such as argon or helium. When used for MIG welding, CO2 use is sometimes referred to as MAG welding, for Metal Active Gas, as CO2 can react at these high temperatures HP Pavilion dv6-1270ec battery. It tends to produce a hotter puddle than truly inert atmospheres, improving the flow characteristics. Although, this may be due to atmospheric reactions occurring at the puddle site. This is usually the opposite of the desired effect when welding, as it tends to embrittle the site, but may not be a problem for general mild steel welding, where ultimate ductility is not a major concern HP Pavilion dv6-1268tx battery. It is used in many consumer products that require pressurized gas because it is inexpensive and nonflammable, and because it undergoes a phase transition from gas to liquid at room temperature at an attainable pressure of approximately 60 bar (870 psi, 59 atm), allowing far more carbon dioxide to fit in a given container than otherwise would HP Pavilion dv6-1268nr battery. Life jackets often contain canisters of pressured carbon dioxide for quick inflation. Aluminum capsules of CO2 are also sold as supplies of compressed gas for airguns, paintball markers, inflating bicycle tires, and for making carbonated water. Rapid vaporization of liquid carbon dioxide is used for blasting in coal mines. High concentrations of carbon dioxide can also be used to kill pests HP Pavilion dv6-1266el battery. Liquid carbon dioxide is used in supercritical drying of some food products and technological materials, in the preparation of specimens for scanning electron microscopy and in the decaffeination of coffee beans. [edit]Fire extinguisher Carbon dioxide extinguishes flames, and some fire extinguishers, especially those designed for electrical fires, contain liquid carbon dioxide under pressure. Carbon dioxide extinguishers work well on small flammable liquid and electrical fires HP Pavilion dv6-1265tx battery, but not on ordinary combustible fires, because although it excludes oxygen, it does not cool the burning substances significantly and when the carbon dioxide disperses they are free to catch fire upon exposure to atmospheric oxygen. Carbon dioxide has also been widely used as an extinguishing agent in fixed fire protection systems for local application of specific hazards and total flooding of a protected space HP Pavilion dv6-1265sg battery.[25] International Maritime Organization standards also recognize carbon dioxide systems for fire protection of ship holds and engine rooms. Carbon dioxide based fire protection systems have been linked to several deaths, because it does not support life in the concentrations used to extinguish fire (40% or so), however, it is not considered to be toxic to humans HP Pavilion dv6-1264tx battery. A review of CO2 systems identified 51 incidents between 1975 and the date of the report, causing 72 deaths and 145 injuries.[26] [edit]Super critical CO2 as solvent See also: Supercritical carbon dioxide Liquid carbon dioxide is a good solvent for many lipophilic organic compounds and is used to remove caffeine from coffee. Carbon dioxide has attracted attention in the pharmaceutical and other chemical processing industries as a less toxic alternative to more traditional solvents such as organochlorides. It is used by some dry cleaners for this reason (see green chemistry) HP Pavilion dv6-1264ca battery. [edit]Agricultural and biological applications Plants require carbon dioxide to conduct photosynthesis. Greenhouses may (if of large size, must) enrich their atmospheres with additional CO2 to sustain and increase plant growth.[27][28] A photosynthesis-related drop (by a factor less than two) in carbon dioxide concentration in a greenhouse compartment would kill green plants, or, at least, completely stop their growth HP Pavilion dv6-1263cl battery. At very high concentrations (100 times atmospheric concentration, or greater), carbon dioxide can be toxic to animal life, so raising the concentration to 10,000 ppm (1%) or higher for several hours will eliminate pests such as whiteflies and spider mites in a greenhouse.[29] Carbon dioxide is used in greenhouses as the main carbon source for Spirulina algae HP Pavilion dv6-1261tx battery. In medicine, up to 5% carbon dioxide (130 times atmospheric concentration) is added to oxygen for stimulation of breathing after apnea and to stabilize the O2/CO2 balance in blood. It has been proposed that carbon dioxide from power generation be bubbled into ponds to grow algae that could then be converted into biodiesel fuel HP Pavilion dv6-1260tx battery.[30] [edit]Oil recovery Carbon dioxide is used in enhanced oil recovery where it is injected into or adjacent to producing oil wells, usually under supercritical conditions. This kind of production may increase original oil recovery by 7 per cent to 23 per cent further from primary extraction.[31]It acts as both a pressurizing agent and, when dissolved into the underground crude oil HP Pavilion dv6-1260sn battery, significantly reduces its viscosity, enabling the oil to flow more rapidly through the earth to the removal well.[32] In mature oil fields, extensive pipe networks are used to carry the carbon dioxide to the injection points. [edit]Refrigerant Liquid and solid carbon dioxide are important refrigerants, especially in the food industry, where they are employed during the transportation and storage of ice cream and other frozen foods HP Pavilion dv6-1260sh battery. Solid carbon dioxide is called "dry ice" and is used for small shipments where refrigeration equipment is not practical. Solid carbon dioxide is always below −78.5 °C at regular atmospheric pressure, regardless of the air temperature. Liquid carbon dioxide (industry nomenclature R744 or R-744) was used as a refrigerant prior to the discovery of R-12 and may enjoy a renaissance due to the fact that r134a contributes to climate change HP Pavilion dv6-1260sg battery. Its physical properties are highly favorable for cooling, refrigeration, and heating purposes, having a high volumetric cooling capacity. Due to its operation at pressures of up to 130 bar (1880 psi), CO2 systems require highly resistant components that have already been developed for mass production in many sectors. In automobile air conditioning, in more than 90% of all driving conditions for latitudes higher than 50° HP Pavilion dv6-1260se battery, R744 operates more efficiently than systems using R-134a. Its environmental advantages (GWP of 1, non-ozone depleting, non-toxic, non-flammable) could make it the future working fluid to replace current HFCs in cars, supermarkets, hot water heat pumps, among others. Coca-Cola has fielded CO2-based beverage coolers and the U.S. Army is interested in CO2 refrigeration and heating technology. HP Pavilion dv6-1260ev batteryThe global automobile industry is expected to decide on the next-generation refrigerant in car air conditioning. CO2 is one discussed option.(see Sustainable automotive air conditioning) [edit]Coal bed methane recovery In enhanced coal bed methane recovery, carbon dioxide is pumped into the coal seam to displace methane.[35] [edit]Niche uses A carbon dioxide laser. Carbon dioxide is so inexpensive and so innocuous, that it finds many small uses that represent what might be called niche uses. For example it is used in the carbon dioxide laser, which is one of the earliest type of lasers HP Pavilion dv6-1260et battery. Carbon dioxide can be used as a mean of controlling the pH of swimming pools, by continuously adding gas to the water, thus keeping the pH level from rising. Among the advantages of this is the avoidance of handling (more hazardous) acids. Similarly, it is also used in the maintaining reef aquaria, where it is commonly used in calcium reactors to temporarily lower the pH HP Pavilion dv6-1260ep batteryof water being passed over calcium carbonate in order to allow the calcium carbonate to dissolve into the water more freely where it is used by some corals to build their skeleton. [edit]In the Earth's atmosphere Carbon dioxide in earth's atmosphere is considered a trace gas currently occurring at an average concentration of about 390 parts per million by volume or 591 parts per million by mass.[36] The total mass of atmospheric carbon dioxide is 3.16×1015 kg (about 3,000 gigatonnes HP Pavilion dv6-1260ej battery). Its concentration varies seasonally (see graph at right) and also considerably on a regional basis, especially near the ground. In urban areas concentrations are generally higher and indoors they can reach 10 times background levels. Carbon dioxide is a greenhouse gas. Yearly increase of atmospheric CO2: In the 1960s, the average annual increase was 37% of the 2000–2007 average.[37] Five hundred million years ago carbon dioxide was 20 times more prevalent than today, decreasing to 4–5 times during the Jurassic period and then slowly declining with a particularly swift reduction occurring 49 million years ago HP Pavilion dv6-1260ei battery.[38][39] Human activities such as the combustion of fossil fuels and deforestation have caused the atmospheric concentration of carbon dioxide to increase by about 35% since the beginning of the age of industrialization.[40] Up to 40% of the gas emitted by some volcanoes during subaerial eruptions is carbon dioxide.[41] It is estimated that volcanoes release about 130–230 million tonnes (145–255 million tons) of CO2 into the atmosphere each year HP Pavilion dv6-1260ec battery. Carbon dioxide is also produced by hot springs such as those at the Bossoleto site near Rapolano Terme in Tuscany, Italy. Here, in a bowl-shaped depression of about 100 m diameter, local concentrations of CO2 rise to above 75% overnight, sufficient to kill insects and small animals, but it warms rapidly when sunlit and the gas is dispersed by convection during the day HP Pavilion dv6-1259tx battery.[42] Locally high concentrations of CO2, produced by disturbance of deep lake water saturated with CO2 are thought to have caused 37 fatalities at Lake Monoun, Cameroon in 1984 and 1700 casualties at Lake Nyos, Cameroon in 1986.[43] Emissions of CO2 by human activities are currently more than 130 times greater than the quantity emitted by volcanoes, amounting to about 27 billion tonnes per year HP Pavilion dv6-1259dx battery.[44] [edit]In the oceans Main article: Carbon cycle Carbon dioxide dissolves in the ocean to form carbonic acid (H2CO3), bicarbonate (HCO3-) and carbonate (CO32-), and there is about fifty times as much carbon dissolved in the sea water of the oceans as exists in the atmosphere. The oceans act as an enormous carbon sink, and have taken up about a third of CO2 emitted by human activity HP Pavilion dv6-1256tx battery.[45] As the concentration of carbon dioxide increases in the atmosphere, the increased uptake of carbon dioxide into the oceans is causing a measurable decrease in the pH of the oceans which is referred to as ocean acidification. Although the natural absorption of CO2 by the world's oceans helps mitigate the climatic effects of anthropogenic emissions of CO2, results in a decrease in the pH of the oceans HP Pavilion dv6-1255tx battery. This reduciton in pH impacts the biological systems in the oceans, primarily oceanic calcifying organisms. These impacts span the food chain from autotrophs to heterotrophs and include organisms such as coccolithophores, corals, foraminifera, echinoderms, crustaceans and molluscs. Under normal conditions, calcite and aragonite are stable in surface waters since the carbonate ion is at supersaturating concentrations HP Pavilion dv6-1255eg battery. However, as ocean pH falls, so does the concentration of this ion, and when carbonate becomes undersaturated, structures made of calcium carbonate are vulnerable to dissolution. Even if there is no change in the rate of calcification, therefore, the rate of dissolution of calcareous material increases.[46] Research has already found that corals, coccolithophore algae, coralline algae,[54] foraminifera, HP Pavilion dv6-1255ee batteryshellfish[56] and pteropods[57] experience reduced calcification or enhanced dissolution when exposed to elevated CO2. Gas solubility decreases as the temperature of water increases (except when both pressure exceeds 300 bar and temperature exceeds 393 K, only found near deep geothermal vents)[58] and therefore the rate of uptake from the atmosphere decreases as ocean temperatures rise HP Pavilion dv6-1254tx battery. Most of the CO2 taken up by the ocean, which is about 30% of the total released into the atmosphere,[59] forms carbonic acid in equilibrium with bicarbonate. Some of these chemical species are consumed by photosynthestic organisms, that remove carbon from the cycle. Increased CO2 in the atmosphere has led to decreasing alkalinity of seawater HP Pavilion dv6-1253cl battery, and there is concern that this may adversely affect organisms living in the water. In particular, with decreasing alkalinity, the availability of carbonates for forming shells decreases,[60] although there's evidence of increased shell production by certain species under increased CO2 content.[61] NOAA states in their May 2008 "State of the science fact sheet for ocean acidification" that: "The oceans have absorbed about 50% of the carbon dioxide (CO2) released from the burning of fossil fuels, resulting in chemical reactions that lower ocean pH HP Pavilion dv6-1253ca battery. This has caused an increase in hydrogen ion (acidity) of about 30% since the start of the industrial age through a process known as “ocean acidification.” A growing number of studies have demonstrated adverse impacts on marine organisms, including: The rate at which reef-building corals produce their skeletons decreases, while production of numerous varieties of jellyfish increases HP Pavilion dv6-1252tx battery. The ability of marine algae and free-swimming zooplankton to maintain protective shells is reduced. The survival of larval marine species, including commercial fish and shellfish, is reduced." Also, the Intergovernmental Panel on Climate Change (IPCC) writes in their Climate Change 2007: Synthesis Report:[62] "The uptake of anthropogenic carbon since 1750 has led to the ocean becoming more acidic with an average decrease in pH of 0.1 units HP Pavilion dv6-1250us battery. Increasing atmospheric CO2 concentrations lead to further acidification [...] While the effects of observed ocean acidification on the marine biosphere are as yet undocumented, the progressive acidification of oceans is expected to have negative impacts on marine shell-forming organisms (e.g. corals) and their dependent species HP Pavilion dv6-1250ss battery." Some marine calcifying organisms (including coral reefs) have been singled out by major research agencies, including NOAA, OSPAR commission, NANOOS and the IPCC, because their most current research shows that ocean acidification should be expected to impact them negatively.[63] Carbon dioxide is also introduced into the oceans through hydrothermal vents. The Champagne hydrothermal vent HP Pavilion dv6-1250sp battery, found at the Northwest Eifuku volcano at Marianas Trench Marine National Monument, produces almost pure liquid carbon dioxide, one of only two known sites in the world.[64] [edit]Biological role Carbon dioxide is an end product in organisms that obtain energy from breaking down sugars, fats and amino acids with oxygen as part of their metabolism, in a process known as cellular respiration. This includes all plants, animals, many fungi and some bacteria. In higher animals, the carbon dioxide travels in the blood from the body's tissues to the lungs where it is exhaled HP Pavilion dv6-1250sn battery. In plants using photosynthesis, carbon dioxide is absorbed from the atmosphere. [edit]Photosynthesis and carbon fixation Overview of photosynthesis and respiration. Carbon dioxide (at right), together with water, form oxygen and organic compounds (at left) by photosynthesis, which can be respired to water and (CO2). Figure 2. Overview of the Calvin cycle and carbon fixation Carbon fixation is the removal of carbon dioxide from the air and its incorporation into solid compounds. Plants, algae, and many species of bacteria (cyanobacteria) fix carbon and create their own food by photosynthesis HP Pavilion dv6-1250sc battery. Photosynthesis uses carbon dioxide and water to produce sugars and occasionally other organic compounds, releasing oxygen as a waste product. Ribulose-1,5-bisphosphate carboxylase oxygenase, commonly known by the shorter name RuBisCO, is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants to energy-rich molecules such as glucose. It is also thought to be the single most abundant protein on Earth HP Pavilion dv6-1250eq battery.[65] These phototrophs use the products of their photosynthesis as internal food sources and as raw material for the construction of more complex organic molecules, such as polysaccharides, nucleic acids and proteins. These are used for their own growth, and also as the basis for the food chains and webs whereby other organisms, including animals such as ourselves HP Pavilion dv6-1250ep battery, are fed. Some important phototrophs, the coccolithophores synthesise hard calcium carbonate scales. A globally significant species of coccolithophore is Emiliania huxleyi whose calcite scales have formed the basis of many sedimentary rocks such as limestone, where what was previously atmospheric carbon can remain fixed for geological timescales HP Pavilion dv6-1250eo battery. Plants can grow up to 50 percent faster in concentrations of 1,000 ppm CO2 when compared with ambient conditions, though this assumes no change in climate and no limitation on other nutrients.[66] Research has shown that elevated CO2 levels cause increased growth reflected in the harvestable yield of crops, with wheat, rice and soybean all showing increases in yield of 12–14% under elevated CO2 in FACE experiments. HP Pavilion dv6-1250el batteryStudies have shown that increased CO2 leads to fewer stomata developing on plants[69] which leads to reduced water usage.[70] Studies using FACE have shown that increases in CO2 lead to decreased concentration of micronutrients in crop plants.[71] This may have knock-on effects on other parts of ecosystems as herbivores will need to eat more food to gain the same amount of protein. HP Pavilion dv6-1250eg batteryThe concentration of secondary metabolites such as phenylpropanoids and flavonoids can also be altered in plants exposed to high concentrations of CO2.[73] [74]. Plants also emit CO2 during respiration, and so the majority of plants and algae, which use C3 photosynthesis, are only net absorbers during the day. Though a growing forest will absorb many tons of CO2 each year HP Pavilion dv6-1250eb battery, the World Bank writes that a mature forest will produce as much CO2 from respiration and decomposition of dead specimens (e.g., fallen branches) as is used in biosynthesis in growing plants.[75] However six experts in biochemistry, biogeology, forestry and related areas writing in the science journal Nature that "Our results demonstrate that old-growth forests can continue to accumulate carbon HP Pavilion dv6-1249tx battery, contrary to the long-standing view that they are carbon neutral." [76] Mature forests are valuable carbon sinks, helping maintain balance in the Earth's atmosphere. Additionally, and crucially to life on earth, photosynthesis by phytoplankton consumes dissolved CO2 in the upper ocean and thereby promotes the absorption of CO2 from the atmosphere. HP Pavilion dv6-1249eo battery[edit]Toxicity See also: Carbon dioxide poisoning Main symptoms of carbon dioxide toxicity, by increasing volume percent in air.[9] Carbon dioxide content in fresh air (averaged between sea-level and 10 kPa level, i.e., about 30 km altitude) varies between 0.036% (360 ppm) and 0.039% (390 ppm), depending on the location.[78] Adaptation to increased levels of CO2 occurs in humans. Continuous inhalation of CO2 can be tolerated at three percent inspired concentrations for at least one month and four percent inspired concentrations for over a week HP Pavilion dv6-1248eo battery. It was suggested that 2.0 percent inspired concentrations could be used for closed air spaces (e.g. a submarine) since the adaptation is physiological and reversible. Decrement in performance or in normal physical activity does not happen at this level.[79][80] However, it should be noted that submarines have carbon dioxide scrubbers which reduce a significant amount of the CO2 present HP Pavilion dv6-1248ca battery.[81] Acute carbon dioxide physiological effect is hypercapnia or asphyxiation sometimes known by the names given to it by miners: blackdamp (also called choke damp or stythe). Blackdamp is primarily nitrogen and carbon dioxide and kills via suffocation (having displaced oxygen). Miners would try to alert themselves to dangerous levels of blackdamp and other gasses in a mine shaft by bringing a caged canary with them as they worked HP Pavilion dv6-1247tx battery. The canary is more sensitive to environmental gasses than humans and as it became unconscious would stop singing and fall off its perch. The Davy lamp could also detect high levels of blackdamp (which collect near the floor) by burning less brightly, while methane, another suffocating gas and explosion risk would make the lamp burn more brightly) HP Pavilion dv6-1247ez battery. Carbon dioxide differential above outdoor levels at steady state conditions (when the occupancy and ventilation system operation are sufficiently long that CO2 concentration has stabilized) are sometimes used to estimate ventilation rates per person. CO2 is considered to be a surrogate for human bio-effluents and may correlate with other indoor pollutants HP Pavilion dv6-1247et battery. Higher CO2 concentrations are associated with occupant health, comfort and performance degradation. ASHRAE Standard 62.1–2007 ventilation rates may result in indoor levels up to 2,100 ppm above ambient outdoor conditions. Thus if the outdoor ambient is 400 ppm, indoor levels may reach 2,500 ppm with ventilation rates that meet this industry consensus standard. Levels in poorly ventilated spaces can be found even higher than this (range of 3,000 or 4,000) HP Pavilion dv6-1247eo battery. [edit]Human physiology [edit]Content The body produces approximately 2.3 pounds (1 kg) of carbon dioxide per day per person.[82] In humans, this carbon dioxide is carried through the venous system and is breathed out through the lungs. Therefore, the carbon dioxide content in the body is high in the venous system, and decreases in the respiratory system, resulting in lower levels along any arterial system HP Pavilion dv6-1247cl battery. Carbon dioxide content in this sense is often given as the partial pressure, which is the pressure which carbon dioxide would have had if it alone occupied the volume.[83] In humans, the carbon dioxide contents are as follows: Transport in the blood CO2 is carried in blood in three different ways. (The exact percentages vary depending whether it is arterial or venous blood). Most of it (about 70% to 80%) is converted to bicarbonate ions HCO− 3 by the enzyme carbonic anhydrase in the red blood cells,[87] by the reaction CO2 + H2O → H2CO3 → H+ + HCO− HP Pavilion dv6-1246tx battery3.5% – 10% is dissolved in the plasma[87] 5% – 10% is bound to hemoglobin as carbamino compounds[87] Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However, the CO2 bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because of allosteric effects on the hemoglobin molecule HP Pavilion dv6-1246eo battery, the binding of CO2 decreases the amount of oxygen that is bound for a given partial pressure of oxygen. The decreased binding to carbon dioxide in the blood due to increased oxygen levels is known as the Haldane Effect, and is important in the transport of carbon dioxide from the tissues to the lungs. Conversely, a rise in the partial pressure of CO2 or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the Bohr Effect HP Pavilion dv6-1245et battery. [edit]Regulation of respiration Carbon dioxide is one of the mediators of local autoregulation of blood supply. If its levels are high, the capillaries expand to allow a greater blood flow to that tissue. Bicarbonate ions are crucial for regulating blood pH. A person's breathing rate influences the level of CO2 in their blood. Breathing that is too slow or shallow causes respiratory acidosis, while breathing that is too rapid leads to hyperventilation, which can cause respiratory alkalosis HP Pavilion dv6-1245es battery. Although the body requires oxygen for metabolism, low oxygen levels normally do not stimulate breathing. Rather, breathing is stimulated by higher carbon dioxide levels. As a result, breathing low-pressure air or a gas mixture with no oxygen at all (such as pure nitrogen) can lead to loss of consciousness without ever experiencing air hunger. This is especially perilous for high-altitude fighter pilots HP Pavilion dv6-1245eo battery. It is also why flight attendants instruct passengers, in case of loss of cabin pressure, to apply the oxygen mask to themselves first before helping others; otherwise, one risks losing consciousness.[87] The respiratory centers try to maintain an arterial CO2 pressure of 40 mm Hg. With intentional hyperventilation, the CO2 content of arterial blood may be lowered to 10–20 mm Hg (the oxygen content of the blood is little affected), and the respiratory drive is diminished HP Pavilion dv6-1245dx battery. This is why one can hold one's breath longer after hyperventilating than without hyperventilating. This carries the risk that unconsciousness may result before the need to breathe becomes overwhelming, which is why hyperventilation is particularly dangerous before free diving.
Photosynthesis is a process used by plants and other organisms to capture the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with carbon dioxide (absorbed from air or water) to form glucose and release oxygen HP Pavilion dv6-1200eh battery. All living cells in turn use fuels derived from glucose and oxidize the hydrogen and carbon to release the sun's energy and reform water and carbon dioxide in the process (cellular respiration).[1] Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can create their own food. In plants, algae, and cyanobacteria HP Pavilion dv6-1200sh battery, photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product. Photosynthesis is vital for all aerobic life on Earth. In addition to maintaining normal levels of oxygen in the atmosphere, photosynthesis is the source of energy for nearly all life on earth, either directly, through primary production, or indirectly, as the ultimate source of the energy in their food HP Pavilion dv6-1200sl battery,[2] the exceptions being chemoautotrophs that live in rocks or around deep sea hydrothermal vents. The rate of energy capture by photosynthesis is immense, approximately 100 terawatts,[3] which is about six times larger than the power consumption of human civilization.[4] As well as energy, photosynthesis is also the source of the carbon in all the organic compounds within organisms' bodies HP Pavilion dv6-1200sq battery. In all, photosynthetic organisms convert around 100–115 petagrams of carbon into biomass per year.[5][6] Although photosynthesis can happen in different ways in different species, some features are always the same. For example, the process always begins when energy from light is absorbed by proteins called photosynthetic reaction centers that contain chlorophylls. In plants, these proteins are held inside organelles called chloroplasts HP Pavilion dv6-1201au battery, while in bacteria they are embedded in the plasma membrane. Some of the light energy gathered by chlorophylls is stored in the form of adenosine triphosphate (ATP). The rest of the energy is used to remove electrons from a substance such as water. These electrons are then used in the reactions that turn carbon dioxide into organic compounds. In plants, algae and cyanobacteria HP Pavilion dv6-1201ax battery, this is done by a sequence of reactions called the Calvin cycle, but different sets of reactions are found in some bacteria, such as the reverse Krebs cycle in Chlorobium. Many photosynthetic organisms have adaptations that concentrate or store carbon dioxide. This helps reduce a wasteful process called photorespiration that can consume part of the sugar produced during photosynthesis HP Pavilion dv6-1201tx battery. Schematic of photosynthesis in plants The first photosynthetic organisms probably evolved about 3,500 million years ago, early in the evolutionary history of life, when all forms of life on Earth were microorganisms and the atmosphere had much more carbon dioxide. They most likely used hydrogen or hydrogen sulfide as sources of electrons, rather than water.[7] Cyanobacteria appeared later HP Pavilion dv6-1202au battery, around 3,000 million years ago, and drastically changed the Earth when they began to oxygenate the atmosphere, beginning about 2,400 million years ago.[8] This new atmosphere allowed the evolution of complex life such as protists. Eventually, no later than a billion years ago, one of these protists formed a symbiotic relationship with a cyanobacterium, producing the ancestor of many plants and algae HP Pavilion dv6-1202ax battery.[9] The chloroplasts in modern plants are the descendants of these ancient symbiotic cyanobacteria.[10] Overview Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar. Photosynthetic organisms are photoautotrophs, which means that they are repositories of energy, they are able to synthesize food directly from carbon dioxide, water HP Pavilion dv6-1202tu battery, and using energy from light. They accrue it as part of their potential energy. However, not all organisms that use light as a source of energy carry out photosynthesis, since photoheterotrophs use organic compounds, rather than carbon dioxide, as a source of carbon.[2] In plants, algae and cyanobacteria, photosynthesis releases oxygen. This is called oxygenic photosynthesis HP Pavilion dv6-1203tu battery. Although there are some differences between oxygenic photosynthesis in plants, algae and cyanobacteria, the overall process is quite similar in these organisms. However, there are some types of bacteria that carry out anoxygenic photosynthesis, which consumes carbon dioxide but does not release oxygen. Carbon dioxide is converted into sugars in a process called carbon fixation HP Pavilion dv6-1203tx battery. Carbon fixation is a redox reaction, so photosynthesis needs to supply both a source of energy to drive this process, and the electrons needed to convert carbon dioxide into a carbohydrate, which is a reduction reaction. In general outline, photosynthesis is the opposite of cellular respiration, where glucose and other compounds are oxidized to produce carbon dioxide, water, and release chemical energy HP Pavilion dv6-1204au battery. However, the two processes take place through a different sequence of chemical reactions and in different cellular compartments. The general equation for photosynthesis is therefore: 2n CO2 + 2n DH2 + photons → 2(CH2O)n + 2n DO Carbon dioxide + electron donor + light energy → carbohydrate + oxidized electron donor In oxygenic photosynthesis water is the electron donor and, since its hydrolysis releases oxygen, the equation for this process is: 2n CO2 + 4n H2O + photons → 2(CH2O)n + 2n O2 + 2n H2O carbon dioxide + water + light energy → carbohydrate + oxygen + water Often 2n water molecules are cancelled on both sides, yielding: 2n CO2 + 2n H2O + photons → 2(CH2O)n + 2n O2 carbon dioxide + water + light energy → carbohydrate + oxygen HP Pavilion dv6-1204ax batteryOther processes substitute other compounds (such as arsenite) for water in the electron-supply role; the microbes use sunlight to oxidize arsenite to arsenate:[11] The equation for this reaction is: CO2 + (AsO33–) + photons → (AsO43–) + CO[12] carbon dioxide + arsenite + light energy → arsenate + carbon monoxide (used to build other compounds in subsequent reactions) HP Pavilion dv6-1204tx batteryPhotosynthesis occurs in two stages. In the first stage, light-dependent reactions or light reactions capture the energy of light and use it to make the energy-storage molecules ATP and NADPH. During the second stage, the light-independent reactions use these products to capture and reduce carbon dioxide HP Pavilion dv6-1205ee battery. Most organisms that utilize photosynthesis to produce oxygen use visible light to do so, although at least three use infrared radiation.[13] Photosynthetic membranes and organelles The proteins that gather light for photosynthesis are embedded within cell membranes. The simplest way these are arranged is in photosynthetic bacteria, where these proteins are held within the plasma membrane HP Pavilion dv6-1205er battery.[14] However, this membrane may be tightly folded into cylindrical sheets called thylakoids,[15] or bunched up into round vesicles called intracytoplasmic membranes.[16] These structures can fill most of the interior of a cell, giving the membrane a very large surface area and therefore increasing the amount of light that the bacteria can absorb HP Pavilion dv6-1205sf battery.[15] In plants and algae, photosynthesis takes place in organelles called chloroplasts. A typical plant cell contains about 10 to 100 chloroplasts. The chloroplast is enclosed by a membrane. This membrane is composed of a phospholipid inner membrane, a phospholipid outer membrane, and an intermembrane space between them. Within the membrane is an aqueous fluid called the stroma HP Pavilion dv6-1205sg battery. The stroma contains stacks (grana) of thylakoids, which are the site of photosynthesis. The thylakoids are flattened disks, bounded by a membrane with a lumen or thylakoid space within it. The site of photosynthesis is the thylakoid membrane, which contains integral and peripheral membrane protein complexes, including the pigments that absorb light energy, which form the photosystems HP Pavilion dv6-1205sl battery. Plants absorb light primarily using the pigment chlorophyll, which is the reason that most plants have a green color. Besides chlorophyll, plants also use pigments such as carotenes and xanthophylls.[17] Algae also use chlorophyll, but various other pigments are present as phycocyanin, carotenes, and xanthophylls in green algae, phycoerythrin in red algae (rhodophytes) and fucoxanthin in brown algae and diatoms resulting in a wide variety of colors HP Pavilion dv6-1205tx battery. These pigments are embedded in plants and algae in special antenna-proteins. In such proteins all the pigments are ordered to work well together. Such a protein is also called a light-harvesting complex. Although all cells in the green parts of a plant have chloroplasts, most of the energy is captured in the leaves. The cells in the interior tissues of a leaf, called the mesophyll, can contain between 450,000 and 800,000 chloroplasts for every square millimeter of leaf HP Pavilion dv6-1206au battery. The surface of the leaf is uniformly coated with a water-resistant waxy cuticle that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place HP Pavilion dv6-1206tx battery. Light reactions Light-dependent reactions of photosynthesis at the thylakoid membrane Main article: Light-dependent reactions In the light reactions, one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron is passed to a modified form of chlorophyll called pheophytin, which passes the electron to a quinone molecule, allowing the start of a flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP to NADPH HP Pavilion dv6-1207au battery. In addition, this creates a proton gradient across the chloroplast membrane; its dissipation is used by ATP synthase for the concomitant synthesis of ATP. The chlorophyll molecule regains the lost electron from a water molecule through a process called photolysis, which releases a dioxygen (O2) molecule. The overall equation for the light-dependent reactions under the conditions of non-cyclic electron flow in green plants is:[18] 2 H2O + 2 NADP+ + 3 ADP + 3 Pi + light → 2 NADPH + 2 H+ + 3 ATP + O2 HP Pavilion dv6-1207ax batteryNot all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with peaks for violet-blue and red light. In red algae, the action spectrum overlaps with the absorption spectrum of phycobilins for red blue-green light HP Pavilion dv6-1207sf battery, which allows these algae to grow in deeper waters that filter out the longer wavelengths used by green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms HP Pavilion dv6-1207tx battery. Z scheme The "Z scheme" In plants, light-dependent reactions occur in the thylakoid membranes of the chloroplasts and use light energy to synthesize ATP and NADPH. The light-dependent reaction has two forms: cyclic and non-cyclic. In the non-cyclic reaction, the photons are captured in the light-harvesting antenna complexes of photosystem II by chlorophyll and other accessory pigments HP Pavilion dv6-1208ca battery (see diagram at right). When a chlorophyll molecule at the core of the photosystem II reaction center obtains sufficient excitation energy from the adjacent antenna pigments, an electron is transferred to the primary electron-acceptor molecule, pheophytin, through a process called photoinduced charge separation. These electrons are shuttled through an electron transport chain HP Pavilion dv6-1210ee battery, the so-called Z-scheme shown in the diagram, that initially functions to generate a chemiosmotic potential across the membrane. An ATP synthase enzyme uses the chemiosmotic potential to make ATP during photophosphorylation, whereas NADPH is a product of the terminal redox reaction in the Z-scheme. The electron enters a chlorophyll molecule in Photosystem I HP Pavilion dv6-1210eg battery. The electron is excited due to the light absorbed by the photosystem. A second electron carrier accepts the electron, which again is passed down lowering energies of electron acceptors. The energy created by the electron acceptors is used to move hydrogen ions across the thylakoid membrane into the lumen. The electron is used to reduce the co-enzyme NADP, which has functions in the light-independent reaction HP Pavilion dv6-1210ek battery. The cyclic reaction is similar to that of the non-cyclic, but differs in the form that it generates only ATP, and no reduced NADP (NADPH) is created. The cyclic reaction takes place only at photosystem I. Once the electron is displaced from the photosystem, the electron is passed down the electron acceptor molecules and returns to photosystem I, from where it was emitted, hence the name cyclic reaction HP Pavilion dv6-1210er battery. Water photolysis Main articles: Photodissociation and Oxygen evolution The NADPH is the main reducing agent in chloroplasts, providing a source of energetic electrons to other reactions. Its production leaves chlorophyll with a deficit of electrons (oxidized), which must be obtained from some other reducing agent. The excited electrons lost from chlorophyll in photosystem I are replaced from the electron transport chain by plastocyanin HP Pavilion dv6-1210es battery. However, since photosystem II includes the first steps of the Z-scheme, an external source of electrons is required to reduce its oxidized chlorophyll a molecules. The source of electrons in green-plant and cyanobacterial photosynthesis is water. Two water molecules are oxidized by four successive charge-separation reactions by photosystem II to yield a molecule of diatomic oxygen and four hydrogen ions HP Pavilion dv6-1210et battery; the electron yielded in each step is transferred to a redox-active tyrosine residue that then reduces the photoxidized paired-chlorophyll a species called P680 that serves as the primary (light-driven) electron donor in the photosystem II reaction center. The oxidation of water is catalyzed in photosystem II by a redox-active structure that contains four manganese ions and a calcium ion HP Pavilion dv6-1210ew battery; this oxygen-evolving complex binds two water molecules and stores the four oxidizing equivalents that are required to drive the water-oxidizing reaction. Photosystem II is the only known biological enzyme that carries out this oxidation of water. The hydrogen ions contribute to the transmembrane chemiosmotic potential that leads to ATP synthesis. Oxygen is a waste product of light-dependent reactions HP Pavilion dv6-1210ez battery, but the majority of organisms on Earth use oxygen for cellular respiration, including photosynthetic organisms.[19][20] Light-independent reactions The Calvin cycle Main articles: Calvin cycle, Carbon fixation, and Light-independent reactions In the light-independent or dark reactions the enzyme RuBisCO captures CO2 from the atmosphere and in a process that requires the newly formed NADPH, called the Calvin-Benson Cycle, releases three-carbon sugars, which are later combined to form sucrose and starch. The overall equation for the light-independent reactions in green plants is: HP Pavilion dv6-1210sa battery3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O Overview of the Calvin cycle and carbon fixation To be more specific, carbon fixation produces an intermediate product, which is then converted to the final carbohydrate products. The carbon skeletons produced by photosynthesis are then variously used to form other organic compounds, such as the building material cellulose, as precursors for lipid and amino acid biosynthesis HP Pavilion dv6-1210sb battery, or as a fuel in cellular respiration. The latter occurs not only in plants but also in animals when the energy from plants gets passed through a food chain. The fixation or reduction of carbon dioxide is a process in which carbon dioxide combines with a five-carbon sugar, ribulose 1,5-bisphosphate (RuBP), to yield two molecules of a three-carbon compound, glycerate 3-phosphate (GP), also known as 3-phosphoglycerate (PGA). GP, in the presence of ATP and NADPH from the light-dependent stages HP Pavilion dv6-1210sf battery, is reduced to glyceraldehyde 3-phosphate (G3P). This product is also referred to as 3-phosphoglyceraldehyde (PGAL) or even as triose phosphate. Triose is a 3-carbon sugar (see carbohydrates). Most (5 out of 6 molecules) of the G3P produced is used to regenerate RuBP so the process can continue (see Calvin-Benson cycle) HP Pavilion dv6-1210sl battery. The 1 out of 6 molecules of the triose phosphates not "recycled" often condense to form hexose phosphates, which ultimately yield sucrose, starch and cellulose. The sugars produced during carbon metabolism yield carbon skeletons that can be used for other metabolic reactions like the production of amino acids and lipids HP Pavilion dv6-1210sr battery. Carbon concentrating mechanisms On land Overview of C4 carbon fixation In hot and dry conditions, plants close their stomata to prevent the loss of water. Under these conditions, CO2 will decrease, and oxygen gas, produced by the light reactions of photosynthesis, will decrease in the stem, not leaves, causing an increase of photorespiration by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase and decrease in carbon fixation HP Pavilion dv6-1210sv battery. Some plants have evolved mechanisms to increase the CO2 concentration in the leaves under these conditions. Main article: C4 carbon fixation C4 plants chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalyzed by an enzyme called PEP carboxylase, creating the four-carbon organic acid oxaloacetic acid. Oxaloacetic acid or malate synthesized by this process is then translocated to specialized bundle sheath cells where the enzyme RuBisCO and other Calvin cycle enzymes are located HP Pavilion dv6-1210tx battery, and where CO2 released by decarboxylation of the four-carbon acids is then fixed by RuBisCO activity to the three-carbon sugar 3-phosphoglyceric acids. The physical separation of RuBisCO from the oxygen-generating light reactions reduces photorespiration and increases CO2 fixation and, thus, photosynthetic capacity of the leaf.[21] C4 plants can produce more sugar than C3 plants in conditions of high light and temperature HP Pavilion dv6-1211ax battery. Many important crop plants are C4 plants, including maize, sorghum, sugarcane, and millet. Plants that do not use PEP-carboxylase in carbon fixation are called C3 plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon sugar 3-phosphoglyceric acids directly in the Calvin-Benson cycle. Over 90% of plants use C3 carbon fixation, compared to 3% that use C4 carbon fixation HP Pavilion dv6-1211er battery.[22] Main article: CAM photosynthesis Xerophytes, such as cacti and most succulents, also use PEP carboxylase to capture carbon dioxide in a process called Crassulacean acid metabolism (CAM). In contrast to C4 metabolism, which physically separates the CO2 fixation to PEP from the Calvin cycle, CAM temporally separates these two processes. CAM plants have a different leaf anatomy from C3 plants HP Pavilion dv6-1211sa battery, and fix the CO2 at night, when their stomata are open. CAM plants store the CO2 mostly in the form of malic acid via carboxylation of phosphoenolpyruvate to oxaloacetate, which is then reduced to malate. Decarboxylation of malate during the day releases CO2 inside the leaves, thus allowing carbon fixation to 3-phosphoglycerate by RuBisCO. Sixteen thousand species of plants use CAM. HP Pavilion dv6-1211sg batteryIn water Cyanobacteria possess carboxysomes, which increase the concentration of CO2 around RuBisCO to increase the rate of photosynthesis. An enzyme, carbonic anhydrase, located within the carboxysome releases CO2 from the dissolved hydrocarbonate ions (HCO3–). Before the CO2 diffuses out it is quickly sponged up by RuBisCO, which is concentrated within the carboxysomes HP Pavilion dv6-1211tx battery. HCO3– ions are made from CO2 outside the cell by another carbonic anhydrase and are actively pumped into the cell by a membrane protein. They cannot cross the membrane as they are charged, and within the cytosol they turn back into CO2 very slowy without the help of carbonic anhydrase. This causes the HCO3– ions to accumulate within the cell from where they diffuse into the carboxysomes. HP Pavilion dv6-1212sl battery Pyrenoids in algae and hornworts also act to concentrate CO2 around rubisco.[25] Order and kinetics Efficiency Measuring the photosynthetic efficiency of wheat in the field using an LCpro-SD Main article: Photosynthetic efficiency Plants usually convert light into chemical energy with a photosynthetic efficiency of 3–6%.[26] Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of carbon dioxide in the atmosphere, and can vary from 0.1% to 8%. HP Pavilion dv6-1212tx battery By comparison, solar panels convert light into electric energy at an efficiency of approximately 6–20% for mass-produced panels, and above 40% in laboratory devices. Photosynthesis measurement systems are not designed to directly measure the amount of light absorbed by the leaf. Nevertheless, the light response curves that systems like the LCpro-SD produce, do allow comparisons in photosynthetic efficiency between plants HP Pavilion dv6-1213ax battery. Evolution Plant cells with visible chloroplasts (from a moss, Plagiomnium affine) Early photosynthetic systems, such as those from green and purple sulfur and green and purple nonsulfur bacteria, are thought to have been anoxygenic, using various molecules as electron donors. Green and purple sulfur bacteria are thought to have used hydrogen and sulfur as an electron donor. Green nonsulfur bacteria used various amino and other organic acids HP Pavilion dv6-1213tx battery. Purple nonsulfur bacteria used a variety of nonspecific organic molecules. The use of these molecules is consistent with the geological evidence that the atmosphere was highly reduced at that time.[citation needed] Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old.[28][29] The main source of oxygen in the atmosphere is oxygenic photosynthesis, and its first appearance is sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis HP Pavilion dv6-1214ax battery, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor, which is oxidized to molecular oxygen (O2) in the photosynthetic reaction center HP Pavilion dv6-1214sl battery. Symbiosis and the origin of chloroplasts Several groups of animals have formed symbiotic relationships with photosynthetic algae. These are most common in corals, sponges and sea anemones. It is presumed that this is due to the particularly simple body plans and large surface areas of these animals compared to their volumes. HP Pavilion dv6-1214tx batteryIn addition, a few marine mollusks Elysia viridis and Elysia chlorotica also maintain a symbiotic relationship with chloroplasts they capture from the algae in their diet and then store in their bodies. This allows the mollusks to survive solely by photosynthesis for several months at a time.[31][32] Some of the genes from the plant cell nucleus have even been transferred to the slugs, so that the chloroplasts can be supplied with proteins that they need to survive. HP Pavilion dv6-1215ax batteryAn even closer form of symbiosis may explain the origin of chloroplasts. Chloroplasts have many similarities with photosynthetic bacteria, including a circular chromosome, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center.[34][35] The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis) by early eukaryotic cells to form the first plant cells HP Pavilion dv6-1215ee battery. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like mitochondria, chloroplasts still possess their own DNA, separate from the nuclear DNA of their plant host cells and the genes in this chloroplast DNA resemble those in cyanobacteria.[36] DNA in chloroplasts codes for redox proteins such as photosynthetic reaction centers. The CoRR Hypothesis proposes that this Co-location is required for Redox Regulation HP Pavilion dv6-1215ei battery. Cyanobacteria and the evolution of photosynthesis The biochemical capacity to use water as the source for electrons in photosynthesis evolved once, in a common ancestor of extant cyanobacteria. The geological record indicates that this transforming event took place early in Earth's history, at least 2450–2320 million years ago (Ma), and, it is speculated, much earlier.[37] Available evidence from geobiological studies of Archean (>2500 Ma) HP Pavilion dv6-1215er battery sedimentary rocks indicates that life existed 3500 Ma, but the question of when oxygenic photosynthesis evolved is still unanswered. A clear paleontological window on cyanobacterial evolution opened about 2000 Ma, revealing an already-diverse biota of blue-greens. Cyanobacteria remained principal primary producers throughout the Proterozoic Eon (2500–543 Ma) HP Pavilion dv6-1215ew battery, in part because the redox structure of the oceans favored photoautotrophs capable of nitrogen fixation.[citation needed] Green algae joined blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the Mesozoic (251–65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did primary production in marine shelf waters take modern form HP Pavilion dv6-1215ez battery. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine algae.[38] A 2010 study by researchers at Tel Aviv University discovered that the Oriental hornet (Vespa orientalis) converts sunlight into electric power using a pigment called xanthopterin. This is the first scientific evidence of a member of the animal kingdom engaging in photosynthesis HP Pavilion dv6-1215sa battery.[39] Discovery Although some of the steps in photosynthesis are still not completely understood, the overall photosynthetic equation has been known since the 19th century. Jan van Helmont began the research of the process in the mid-17th century when he carefully measured the mass of the soil used by a plant and the mass of the plant as it grew. After noticing that the soil mass changed very little HP Pavilion dv6-1215sd battery, he hypothesized that the mass of the growing plant must come from the water, the only substance he added to the potted plant. His hypothesis was partially accurate — much of the gained mass also comes from carbon dioxide as well as water. However, this was a signaling point to the idea that the bulk of a plant's biomass comes from the inputs of photosynthesis, not the soil itself HP Pavilion dv6-1215sf battery. Joseph Priestley, a chemist and minister, discovered that, when he isolated a volume of air under an inverted jar, and burned a candle in it, the candle would burn out very quickly, much before it ran out of wax. He further discovered that a mouse could similarly "injure" air. He then showed that the air that had been "injured" by the candle and the mouse could be restored by a plant HP Pavilion dv6-1215sg battery. In 1778, Jan Ingenhousz, court physician to the Austrian Empress, repeated Priestley's experiments. He discovered that it was the influence of sunlight on the plant that could cause it to revive a mouse in a matter of hours. In 1796, Jean Senebier, a Swiss pastor, botanist, and naturalist, demonstrated that green plants consume carbon dioxide and release oxygen under the influence of light HP Pavilion dv6-1215sl battery. Soon afterward, Nicolas-Théodore de Saussure showed that the increase in mass of the plant as it grows could not be due only to uptake of CO2 but also to the incorporation of water. Thus, the basic reaction by which photosynthesis is used to produce food (such as glucose) was outlined HP Pavilion dv6-1215ss battery. Cornelis Van Niel made key discoveries explaining the chemistry of photosynthesis. By studying purple sulfur bacteria and green bacteria he was the first scientist to demonstrate that photosynthesis is a light-dependent redox reaction, in which hydrogen reduces carbon dioxide HP Pavilion dv6-1215tx battery. Robert Emerson discovered two light reactions by testing plant productivity using different wavelengths of light. With the red alone, the light reactions were suppressed. When blue and red were combined, the output was much more substantial. Thus, there were two photosystems, one absorbing up to 600 nm wavelengths, the other up to 700 nm. The former is known as PSII HP Pavilion dv6-1216ax battery, the latter is PSI. PSI contains only chlorophyll a, PSII contains primarily chlorophyll a with most of the available chlorophyll b, among other pigment. These include phycobilins, which are the red and blue pigments of red and blue algae respectively, and fucoxanthol for brown algae and diatoms. The process is most productive when absorption of quanta are equal in both the PSII and PSI, assuring that input energy from the antenna complex is divided between the PSI and PSII system HP Pavilion dv6-1216er battery, which in turn powers the photochemistry.[6] Robert Hill thought that a complex of reactions consisting of an intermediate to cytochrome b6 (now a plastoquinone), another is from cytochrome f to a step in the carbohydrate-generating mechanisms. These are linked by plastoquinone, which does require energy to reduce cytochrome f for it is a sufficient reductant HP Pavilion dv6-1216sa battery. Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water, were performed by Hill in 1937 and 1939. He showed that isolated chloroplasts give off oxygen in the presence of unnatural reducing agents like iron oxalate, ferricyanide or benzoquinone after exposure to light. The Hill reaction is as follows HP Pavilion dv6-1216sl battery: 2 H2O + 2 A + (light, chloroplasts) → 2 AH2 + O2 where A is the electron acceptor. Therefore, in light, the electron acceptor is reduced and oxygen is evolved. Samuel Ruben and Martin Kamen used radioactive isotopes to determine that the oxygen liberated in photosynthesis came from the water. Melvin Calvin and Andrew Benson, along with James Bassham, elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants HP Pavilion dv6-1216ss battery. The carbon reduction cycle is known as the Calvin cycle, which ignores the contribution of Bassham and Benson. Many scientists refer to the cycle as the Calvin-Benson Cycle, Benson-Calvin, and some even call it the Calvin-Benson-Bassham (or CBB) Cycle. Nobel Prize-winning scientist Rudolph A. Marcus was able to discover the function and significance of the electron transport chain HP Pavilion dv6-1216tx battery. Otto Heinrich Warburg and Dean Burk discovered the I-quantum photosynthesis reaction that splits the CO2, activated by the respiration.[40] Louis N.M. Duysens and Jan Amesz discovered that chlorophyll a will absorb one light, oxidize cytochrome f, chlorophyll a (and other pigments) will absorb another light, but will reduce this same oxidized cytochrome, stating the two light reactions are in series HP Pavilion dv6-1217ax battery. Factors The leaf is the primary site of photosynthesis in plants. There are three main factors affecting photosynthesis and several corollary factors. The three main are: Light irradiance and wavelength Carbon dioxide concentration Temperature. Light intensity (irradiance), wavelength and temperature In the early 20th century, Frederick Frost Blackman along with Albert Einstein investigated the effects of light intensity (irradiance) and temperature on the rate of carbon assimilation. At constant temperature, the rate of carbon assimilation varies with irradiance, initially increasing as the irradiance increases. However, at higher irradiance, this relationship no longer holds and the rate of carbon assimilation reaches a plateau HP Pavilion dv6-1217er battery. At constant irradiance, the rate of carbon assimilation increases as the temperature is increased over a limited range. This effect is seen only at high irradiance levels. At low irradiance, increasing the temperature has little influence on the rate of carbon assimilation. These two experiments illustrate vital points: First, from research it is known that, in general, photochemical reactions are not affected by temperature HP Pavilion dv6-1217ss battery. However, these experiments clearly show that temperature affects the rate of carbon assimilation, so there must be two sets of reactions in the full process of carbon assimilation. These are, of course, the light-dependent 'photochemical' stage and the light-independent, temperature-dependent stage. Second, Blackman's experiments illustrate the concept of limiting factors. Another limiting factor is the wavelength of light. Cyanobacteria HP Pavilion dv6-1217tx battery, which reside several meters underwater, cannot receive the correct wavelengths required to cause photoinduced charge separation in conventional photosynthetic pigments. To combat this problem, a series of proteins with different pigments surround the reaction center. This unit is called a phycobilisome. Carbon dioxide levels and photorespiration As carbon dioxide concentrations rise, the rate at which sugars are made by the light-independent reactions increases until limited by other factors HP Pavilion dv6-1218ca battery. RuBisCO, the enzyme that captures carbon dioxide in the light-independent reactions, has a binding affinity for both carbon dioxide and oxygen. When the concentration of carbon dioxide is high, RuBisCO will fix carbon dioxide. However, if the carbon dioxide concentration is low, RuBisCO will bind oxygen instead of carbon dioxide. This process, called photorespiration, uses energy, but does not produce sugars HP Pavilion dv6-1218ss battery. RuBisCO oxygenase activity is disadvantageous to plants for several reasons: One product of oxygenase activity is phosphoglycolate (2 carbon) instead of 3-phosphoglycerate (3 carbon). Phosphoglycolate cannot be metabolized by the Calvin-Benson cycle and represents carbon lost from the cycle. A high oxygenase activity, therefore, drains the sugars that are required to recycle ribulose 5-bisphosphate and for the continuation of the Calvin-Benson cycle HP Pavilion dv6-1218tx battery. Phosphoglycolate is quickly metabolized to glycolate that is toxic to a plant at a high concentration; it inhibits photosynthesis. Salvaging glycolate is an energetically expensive process that uses the glycolate pathway, and only 75% of the carbon is returned to the Calvin-Benson cycle as 3-phosphoglycerate. The reactions also produce ammonia (NH3), which is able to diffuse out of the plant, leading to a loss of nitrogen HP Pavilion dv6-1219ez battery. A highly simplified summary is: 2 glycolate + ATP → 3-phosphoglycerate + carbon dioxide + ADP + NH3 The salvaging pathway for the products of RuBisCO oxygenase activity is more commonly known as photorespiration, since it is characterized by light-dependent oxygen consumption and the release of carbon dioxide. Chlorophyll (also chlorophyl) is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros ("green") and φύλλον HP Pavilion dv6-1219tx battery, phyllon ("leaf"). Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to absorb energy from light. Chlorophyll absorbs light most strongly in the blue portion of the electromagnetic spectrum, followed by the red portion. However, it is a poor absorber of green and near-green portions of the spectrum, hence the green color of chlorophyll-containing tissues HP Pavilion dv6-1220ec battery.[1] Chlorophyll was first isolated by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817.[2] Chlorophyll and photosynthesis Chlorophyll is vital for photosynthesis, which allows plants to absorb energy from light. Chlorophyll molecules are specifically arranged in and around photosystems that are embedded in the thylakoid membranes of chloroplasts. In these complexes, chlorophyll serves two primary functions. The function of the vast majority of chlorophyll HP Pavilion dv6-1220eg battery (up to several hundred molecules per photosystem) is to absorb light and transfer that light energy by resonance energy transfer to a specific chlorophyll pair in the reaction center of the photosystems. The two currently accepted photosystem units are Photosystem II and Photosystem I, which have their own distinct reaction center chlorophylls, named P680 and P700, respectively.[3] These pigments are named after the wavelength (in nanometers) of their red-peak absorption maximum HP Pavilion dv6-1220ei battery. The identity, function and spectral properties of the types of chlorophyll in each photosystem are distinct and determined by each other and the protein structure surrounding them. Once extracted from the protein into a solvent (such as acetone or methanol),[4][5][6] these chlorophyll pigments can be separated in a simple paper chromatography experiment and, based on the number of polar groups between chlorophyll a and chlorophyll b, will chemically separate out on the paper HP Pavilion dv6-1220ek battery. The function of the reaction center chlorophyll is to use the energy absorbed by and transferred to it from the other chlorophyll pigments in the photosystems to undergo a charge separation, a specific redox reaction in which the chlorophyll donates an electron into a series of molecular intermediates called an electron transport chain. The charged reaction center chlorophyll (P680+) is then reduced back to its ground state by accepting an electron HP Pavilion dv6-1220er battery. In Photosystem II, the electron that reduces P680+ ultimately comes from the oxidation of water into O2 and H+ through several intermediates. This reaction is how photosynthetic organisms such as plants produce O2 gas, and is the source for practically all the O2 in Earth's atmosphere. Photosystem I typically works in series with Photosystem II; thus the P700+ of Photosystem I is usually reduced HP Pavilion dv6-1220ev battery, via many intermediates in the thylakoid membrane, by electrons ultimately from Photosystem II. Electron transfer reactions in the thylakoid membranes are complex, however, and the source of electrons used to reduce P700+ can vary. The electron flow produced by the reaction center chlorophyll pigments is used to shuttle H+ ions across the thylakoid membrane, setting up a chemiosmotic potential used mainly to produce ATP chemical energy HP Pavilion dv6-1220ew battery; and those electrons ultimately reduce NADP+ to NADPH, a universal reductant used to reduce CO2 into sugars as well as for other biosynthetic reductions. Reaction center chlorophyll–protein complexes are capable of directly absorbing light and performing charge separation events without other chlorophyll pigments, but the absorption cross section (the likelihood of absorbing a photon under a given light intensity) is small HP Pavilion dv6-1220ez battery. Thus, the remaining chlorophylls in the photosystem and antenna pigment protein complexes associated with the photosystems all cooperatively absorb and funnel light energy to the reaction center. Besides chlorophyll a, there are other pigments, called accessory pigments, which occur in these pigment–protein antenna complexes. A green sea slug, Elysia chlorotica, has been found to use the chlorophyll it has eaten to perform photosynthesis for itself HP Pavilion dv6-1220sa battery. This process is known as kleptoplasty, and no other animal has been found to have this ability. [edit]Why green and not black? Black plants can absorb more radiation, and yet most plants are green It still is unclear exactly why plants have mostly evolved to be green. Green plants reflect mostly green and near-green light to viewers rather than absorbing it. Other parts of the system of photosynthesis still allow green plants to use the green light spectrum (e.g., through a light-trapping leaf structure, carotenoids, etc.) HP Pavilion dv6-1220sb battery. Green plants do not use a large part of the visible spectrum as efficiently as possible. A black plant can absorb more radiation, and this could be very useful, if extra heat produced is effectively disposed of (e.g., some plants must close their openings, called stomata, on hot days to avoid losing too much water, which leaves only conduction, convection, and radiative heat-loss as solutions) HP Pavilion dv6-1220sd battery.[7] The question becomes why the only light-absorbing molecule used for power in plants is green and not simply black. The biologist John Berman has offered the opinion that evolution is not an engineering process, and so it is often subject to various limitations that an engineer or other designer is not. Even if black leaves were better, evolution's limitations can prevent species from climbing to the absolute highest peak on the fitness landscape. Berman wrote that achieving pigments that work better than chlorophyll could be very difficult HP Pavilion dv6-1220sh battery. In fact, all higher plants (embryophytes) are thought to have evolved from a common ancestor that is a sort of green algae – with the idea being that chlorophyll has evolved only once. [8] Shil DasSarma, a microbial geneticist at the University of Maryland, has pointed out that species of archaea do use another light-absorbing molecule, retinal, to extract power from the green spectrum. He described the view of some scientists that such green-light-absorbing archae once dominated the earth environment HP Pavilion dv6-1220so battery. This could have left open a "niche" for green organisms that would absorb the other wavelengths of sunlight. This is just a possibility, and Berman wrote that scientists are still not convinced of any one explanation.[9] [edit]Chemical structure Space-filling model of the chlorophyll a molecule Chlorophyll is a chlorin pigment, which is structurally similar to and produced through the same metabolic pathway as other porphyrin pigments such as heme. At the center of the chlorin ring is a magnesium ion. At the time of its discovery in the early 1900s HP Pavilion dv6-1220sp battery, this was the first time that this element had been detected in living tissue.[10] For the structures depicted in this article, some of the ligands attached to the Mg2+ center are omitted for clarity. The chlorin ring can have several different side chains, usually including a long phytol chain. There are a few different forms that occur naturally, but the most widely distributed form in terrestrial plants is chlorophyll a HP Pavilion dv6-1220ss battery. After initial work done by German chemist Richard Willstätter spanning from 1905 to 1915, the general structure of chlorophyll a was elucidated by Hans Fischer in 1940. By 1960, when most of the stereochemistry of chlorophyll a was known, Robert Burns Woodward published a total synthesis of the molecule.[10][11] In 1967, the last remaining stereochemical elucidation was completed by Ian Fleming, HP Pavilion dv6-1220st battery and in 1990 Woodward and co-authors published an updated synthesis.[13] Chlorophyll f was announced to be present in cyanobacteria and other oxygenic microorganisms that form stromatolites in 2010;[14][15] a molecular formula of C55H70O6N4Mg and a structure of (2-formyl)-chlorophyll a were deduced based on NMR, optical and mass spectra.[16] The different structures of chlorophyll are summarized below HP Pavilion dv6-1220tx battery: Spectrophotometry Absorbance spectra of free chlorophyll a (green) and b (red) in a solvent. The spectra of chlorophyll molecules are slightly modified in vivo depending on specific pigment-protein interactions. Measurement of the absorption of light is complicated by the solvent used to extract it from plant material, which affects the values obtained, In diethyl ether, chlorophyll a has approximate absorbance maxima of 430 nm and 662 nm, while chlorophyll b has approximate maxima of 453 nm and 642 nm. HP Pavilion dv6-1221ax batteryThe absorption peaks of chlorophyll a are at 665 nm and 465 nm. Chlorophyll a fluoresces at 673 nm (maximum) and 726 nm. The peak molar absorption coefficient of chlorophyll a exceeds 105 M−1 cm−1, which is among the highest for small-molecule organic compounds.[citation needed] In 90% acetone-water, the peak absorption wavelengths of chlorophyll a are 430 nm and 664 nm; peaks for chlorophyll b are 460 nm and 647 nm HP Pavilion dv6-1221eo battery; peaks for chlorophyll c1 are 442 nm and 630 nm; peaks for chlorophyll c2 are 444 nm and 630 nm; peaks for chlorophyll d are 401 nm, 455 nm and 696 nm.[19] Chlorophyll content meter measuring chlorophyll content by absorption By measuring the absorption of light in the red and far red regions it is possible to estimate the concentration of chlorophyll within a leaf.[20] While absorption instruments have been proven over time to work well as a non-destructive test on many types of samples, they do have limitations. Absorption technique limitations HP Pavilion dv6-1221sl battery: The sample to be measured must completely cover the instrument’s aperture, with no holes. Samples must be thin enough to allow transmission of the measuring wavelengths of light. Surfaces must be relatively flat and uniform. Variable fluorescence (the Kautsky induction effect) caused by the red wavelength of absorption instruments, limits the repeatability of measurements at the same location HP Pavilion dv6-1221tx battery. Selection of the measuring area, on smaller leaves, can cause measurement variations due to internal leaf structure variation. Veins and midribs can cause significant variation on samples. Wavelengths used in absorption methods, typically limit linear correlation with chemical chlorophyll content methods to concentration levels below 300 mg/m2.[21] As a result, absorption instruments do not work with conifer needles, turf grasses, Arabidopsis leaves, moss, most CAM plants such as prickly pear cactus HP Pavilion dv6-1222eo battery, and Agave, fruit, stems, petioles, lichens, and algae on rocks. Furthermore, it is difficult to get reliable readings on very small leaf plants such as immature rice and wheat. A superior method is to measure the chlorophyll content using chlorophyll fluorescence. Gitelson (1999) states, "The ratio between chlorophyll fluorescence, at 735 nm and the wavelength range 700nm to 710 nm HP Pavilion dv6-1222et battery, F735/F700 was found to be linearly proportional to the chlorophyll content (with determination coefficient, r2, more than 0.95) and thus this ratio can be used as a precise indicator of chlorophyll content in plant leaves."[21] Non-destructive, hand-held meters use this effect to measure the chlorophyll content of samples where traditional absorbance techniques cannot be used. This new method has many advantages over older, absorption techniques HP Pavilion dv6-1222sl battery. These include Small samples can be analysed for chlorophyll content Samples do not need to fill the measuring aperture, so small samples can be measured. Samples do not need to allow transmission of the measuring beam, so thick samples can be measured. Surfaces do not need to be flat and uniform, so difficult plant morphologies can be measured. No Kautsky induction effect, so measurements can be repeated rapidly at the same sight. Small sample area, so naturally occurring structures like mid ribs and veins can be avoided HP Pavilion dv6-1222tx battery. Higher measuring range (675 mg/m2, as opposed to 300 mg/m2 with absorption techniques), so many more samples can be measured. By measuring chlorophyll fluorescence, plant ecophysiology can be investigated. Chlorophyll fluorometers are used by plant researchers to assess plant stress. [edit]Biosynthesis Further information: Protochlorophyllide In plants, chlorophyll may be synthesized from succinyl-CoA and glycine, although the immediate precursor to chlorophyll a and b is protochlorophyllide HP Pavilion dv6-1223eo battery. In Angiosperm plants, the last step, conversion of protochlorophyllide to chlorophyll, is light-dependent and such plants are pale (etiolated) if grown in the darkness. Non-vascular plants and green algae have an additional light-independent enzyme and grow green in the darkness instead HP Pavilion dv6-1223sf battery. Chlorophyll itself is bound to proteins and can transfer the absorbed energy in the required direction. Protochlorophyllide occurs mostly in the free form and, under light conditions, acts as a photosensitizer, forming highly toxic free radicals. Hence, plants need an efficient mechanism of regulating the amount of chlorophyll precursor. In angiosperms, this is done at the step of aminolevulinic acid (ALA) HP Pavilion dv6-1223sl battery, one of the intermediate compounds in the biosynthesis pathway. Plants that are fed by ALA accumulate high and toxic levels of protochlorophyllide; so do the mutants with the damaged regulatory system.[22] Further information: Chlorosis Chlorosis is a condition in which leaves produce insufficient chlorophyll, turning them yellow. Chlorosis can be caused by a nutrient deficiency of iron--called iron chlorosis—or by a shortage of magnesium or nitrogen HP Pavilion dv6-1224eo battery. Soil pH sometimes plays a role in nutrient-caused chlorosis; many plants are adapted to grow in soils with specific pH levels and their ability to absorb nutrients from the soil can be dependent on this.[23] Chlorosis can also be caused by pathogens including viruses, bacteria and fungal infections, or sap-sucking insects. [edit]Culinary use Chlorophyll is registered as a food additive (colorant), and its E number is E140. Chefs use chlorophyll to color a variety of foods and beverages green HP Pavilion dv6-1225ee battery, such as pasta and absinthe.[24] Chlorophyll is not soluble in water, and it is first mixed with a small quantity of vegetable oil to obtain the desired solution. Extracted liquid chlorophyll was considered to be unstable and always denatured until 1997, when Frank S. & Lisa Sagliano used freeze-drying of liquid chlorophyll at the University of Florida and stabilized it as a powder, preserving it for future use. HP Pavilion dv6-1225ef battery
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental massHP Pavilion dv6-1299lx battery.[5] Non-remnant stars are mainly composed of hydrogen in its plasma state. Naturally occurring elemental hydrogen is relatively rare on Earth.The most common isotope of hydrogen is protium (name rarely used, symbol 1H) with a single proton and no neutrons. In ionic compounds it can take a negative charge (an anion known as a hydride and written as H−), or as a positively charged species H+HP Pavilion dv6-1299ez battery. The latter cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds always occur as more complex species. Hydrogen forms compounds with most elements and is present in water and most organic compoundsHP Pavilion dv6-1299es battery. It plays a particularly important role in acid-base chemistry with many reactions exchanging protons between soluble molecules. As the simplest atom known, the hydrogen atom has been of theoretical use. For example, as the only neutral atom with an analytic solution to the Schrödinger equation, the study of the energetics and bonding of the hydrogen atom played a key role in the development of quantum mechanicsHP Pavilion dv6-1299er battery.Hydrogen gas (now known to be H2) was first artificially produced in the early 16th century, via the mixing of metals with strong acids. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance,[6] and that it produces water when burned, a property which later gave it its nameHP Pavilion dv6-1299eo battery, which in Greek means "water-former." At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, non-toxic, highly combustible diatomic gas with the molecular formula H2.Industrial production is mainly from the steam reforming of natural gas, and less often from more energy-intensive hydrogen production methods like the electrolysis of waterHP Pavilion dv6-1299ef battery.[7] Most hydrogen is employed near its production site, with the two largest uses being fossil fuel processing (e.g., hydrocracking) and ammonia production, mostly for the fertilizer market.Hydrogen is a concern in metallurgy as it can embrittle many metals,[8] complicating the design of pipelines and storage tanksHP Pavilion dv6-1299ea battery.[9]PropertiesCombustionThe Space Shuttle Main Engine burnt hydrogen with oxygen, producing a nearly invisible flame at full thrust.Hydrogen gas (dihydrogen or molecular hydrogen)[10] is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume.[11] The enthalpy of combustion for hydrogen is −286 kJ/mol:[12]2 H2(g) + O2(g) → 2 H2O(l) + 572 kJ (286 kJ/mol)[note 1HP Pavilion dv6-1295el battery]Hydrogen gas forms explosive mixtures with air if it is 4–74% concentrated and with chlorine if it is 5–95% concentrated. The mixtures spontaneously explode by spark, heat or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F) HP Pavilion dv6-1291es battery.[13] Pure hydrogen-oxygen flames emit ultraviolet light and are nearly invisible to the naked eye, as illustrated by the faint plume of the Space Shuttle Main Engine compared to the highly visible plume of a Space Shuttle Solid Rocket Booster. The detection of a burning hydrogen leak may require a flame detector; such leaks can be very dangerousHP Pavilion dv6-1290ev battery. The destruction of the Hindenburg airship was an infamous example of hydrogen combustion; the cause is debated, but the visible flames were the result of combustible materials in the ship's skin.[14] Because hydrogen is buoyant in air, hydrogen flames tend to ascend rapidly and cause less damage than hydrocarbon fires. Two-thirds of the Hindenburg passengers survived the fire, and many deaths were instead the result of falls or burning diesel fuelHP Pavilion dv6-1290es battery.[15]H2 reacts with every oxidizing element. Hydrogen can react spontaneously and violently at room temperature with chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are also potentially dangerous acids. HP Pavilion dv6-1290en batteryElectron energy levelsMain article: Hydrogen atomDepiction of a hydrogen atom with size of central proton shown, and the atomic diameter shown as about twice the Bohr model radius (image not to scale).The ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 92 nm wavelengthHP Pavilion dv6-1290ec battery.[17]The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as "orbiting" the proton in analogy to the Earth's orbit of the Sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravityHP Pavilion dv6-1288la battery. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, and therefore only certain allowed energies.[18]A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment that uses the Schrödinger equation or the Feynman path integral formulation to calculate the probability density of the electron around the protonHP Pavilion dv6-1285es battery.[19] The most complicated treatments allow for the small effects of special relativity and vacuum polarization. In the quantum mechanical treatment, the electron in a ground state hydrogen atom has no angular momentum at all— an illustration of how different the "planetary orbit" conception of electron motion differs from realityHP Pavilion dv6-1282et battery.Elemental molecular formsSee also: Spin isomers of hydrogenFirst tracks observed in liquid hydrogen bubble chamber at the BevatronThere exist two different spin isomers of hydrogen diatomic molecules that differ by the relative spin of their nuclei.[20] In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state with a molecular spin quantum number of 1 (½+½); in the parahydrogen form the spins are antiparallel and form a singlet with a molecular spin quantum number of 0 (½–½)HP Pavilion dv6-1280us battery. At standard temperature and pressure, hydrogen gas contains about 25% of the para form and 75% of the ortho form, also known as the "normal form".[21] The equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but because the ortho form is an excited state and has a higher energy than the para form, it is unstable and cannot be purifiedHP Pavilion dv6-1280sn battery. At very low temperatures, the equilibrium state is composed almost exclusively of the para form. The liquid and gas phase thermal properties of pure parahydrogen differ significantly from those of the normal form because of differences in rotational heat capacities, as discussed more fully in Spin isomers of hydrogen.[22] The ortho/para distinction also occurs in other hydrogen-containing molecules or functional groupsHP Pavilion dv6-1280ev battery, such as water and methylene, but is of little significance for their thermal properties.[23]The uncatalyzed interconversion between para and ortho H2 increases with increasing temperature; thus rapidly condensed H2 contains large quantities of the high-energy ortho form that converts to the para form very slowlyHP Pavilion dv6-1280et battery.[24] The ortho/para ratio in condensed H2 is an important consideration in the preparation and storage of liquid hydrogen: the conversion from ortho to para is exothermic and produces enough heat to evaporate some of the hydrogen liquid, leading to loss of liquefied material. Catalysts for the ortho-para interconversionHP Pavilion dv6-1280es battery, such as ferric oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel[25] compounds, are used during hydrogen cooling.[26]Further information: Hydrogen compoundsCovalent and organic compoundsWhile H2 is not very reactive under standard conditions, it does form compounds with most elements. Hydrogen can form compounds with elements that are more electronegative, such as halogens (e.g., F, Cl, Br, I), or oxygenHP Pavilion dv6-1280ep battery; in these compounds hydrogen takes on a partial positive charge.[27] When bonded to fluorine, oxygen, or nitrogen, hydrogen can participate in a form of medium-strength noncovalent bonding called hydrogen bonding, which is critical to the stability of many biological molecules.[28][29] Hydrogen also forms compounds with less electronegative elementsHP Pavilion dv6-1280el battery, such as the metals and metalloids, in which it takes on a partial negative charge. These compounds are often known as hydrides.[30]Hydrogen forms a vast array of compounds with carbon called the hydrocarbons, and an even vaster array with heteroatoms that, because of their general association with living things, are called organic compoundsHP Pavilion dv6-1277la battery.[31] The study of their properties is known as organic chemistry[32] and their study in the context of living organisms is known as biochemistry.[33] By some definitions, "organic" compounds are only required to contain carbon. However, most of them also contain hydrogenHP Pavilion dv6-1277el battery, and because it is the carbon-hydrogen bond which gives this class of compounds most of its particular chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry.[31] Millions of hydrocarbons are known, and they are usually formed by complicated synthetic pathways, which seldom involve elementary hydrogenHP Pavilion dv6-1275la battery.HydridesCompounds of hydrogen are often called hydrides, a term that is used fairly loosely. The term "hydride" suggests that the H atom has acquired a negative or anionic character, denoted H−, and is used when hydrogen forms a compound with a more electropositive element. The existence of the hydride anionHP Pavilion dv6-1275eg battery, suggested by Gilbert N. Lewis in 1916 for group I and II salt-like hydrides, was demonstrated by Moers in 1920 with the electrolysis of molten lithium hydride (LiH), that produced a stoichiometry quantity of hydrogen at the anode.[34] For hydrides other than group I and II metalsHP Pavilion dv6-1270st battery, the term is quite misleading, considering the low electronegativity of hydrogen. An exception in group II hydrides is BeH2, which is polymeric. In lithium aluminium hydride, the AlH−4 anion carries hydridic centers firmly attached to the Al(III).Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, there are over 100 binary borane hydrides known, but only one binary aluminium hydrideHP Pavilion dv6-1270ss battery.[35] Binary indium hydride has not yet been identified, although larger complexes exist.[36]In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly common in group 13 elements, especially in boranes (boron hydrides) and aluminium complexes, as well as in clustered carboranesHP Pavilion dv6-1270la battery.[37]Protons and acidsFurther information: Acid–base reactionOxidation of hydrogen removes its electron and gives H+, which contains no electrons and a nucleus which is usually composed of one proton. That is why H+ is often called a proton. This species is central to discussion of acids. Under the Bronsted-Lowry theory, acids are proton donors, while bases are proton acceptorsHP Pavilion dv6-1270ev battery.A bare proton, H+, cannot exist in solution or in ionic crystals, because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules, and will remain attached to themHP Pavilion dv6-1270et battery. However, the term 'proton' is sometimes used loosely and metaphorically to refer to positively charged or cationic hydrogen attached to other species in this fashion, and as such is denoted "H+" without any implication that any single protons exist freely as a speciesHP Pavilion dv6-1270eq battery.To avoid the implication of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain a less unlikely fictitious species, termed the "hydronium ion" (H3O+). However, even in this case, such solvated hydrogen cations are thought more realistically physically to be organized into clusters that form species closer to H9O+HP Pavilion dv6-1270el battery4.[38] Other oxonium ions are found when water is in solution with other solvents.[39]Although exotic on earth, one of the most common ions in the universe is the H+3 ion, known as protonated molecular hydrogen or the trihydrogen cation.[40]IsotopesMain article: Isotopes of hydrogenHydrogen discharge (spectrum) tubeDeuterium discharge (spectrum) tubeHP Pavilion dv6-1270eg batteryProtium, the most common isotope of hydrogen, has one proton and one electron. Unique among all stable isotopes, it has no neutrons (see diproton for a discussion of why others do not exist).Hydrogen has three naturally occurring isotopes, denoted 1H, 2H and 3H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not observed in nature. HP Pavilion dv6-1270ec battery1H is the most common hydrogen isotope with an abundance of more than 99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name protium.[43]2H, the other stable hydrogen isotope, is known as deuterium and contains one proton and one neutron in its nucleusHP Pavilion dv6-1268tx battery. Essentially all deuterium in the universe is thought to have been produced at the time of the Big Bang, and has endured since that time. Deuterium is not radioactive, and does not represent a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy waterHP Pavilion dv6-1268nr battery. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy.[44] Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusionHP Pavilion dv6-1266el battery.[45]3H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into helium-3 through beta decay with a half-life of 12.32 years.[37] It is so radioactive that it can be used in luminous paint, making it useful in such things as watchesHP Pavilion dv6-1265tx battery. The glass prevents the small amount of radiation from getting out.[46] Small amounts of tritium occur naturally because of the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weapons tests.[47] It is used in nuclear fusion reactions,[48] as a tracer in isotope geochemistry,[49] and specialized in self-powered lighting devicesHP Pavilion dv6-1265sg battery.[50] Tritium has also been used in chemical and biological labeling experiments as a radiolabel.[51]Hydrogen is the only element that has different names for its isotopes in common use today. During the early study of radioactivity, various heavy radioactive isotopes were given their own names, but such names are no longer used, except for deuterium and tritiumHP Pavilion dv6-1264tx battery. The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium, but the corresponding symbol for protium, P, is already in use for phosphorus and thus is not available for protium.[52] In its nomenclatural guidelines, the International Union of Pure and Applied Chemistry allows any of D, T, 2H, and 3H to be used, although 2H and 3H are preferredHP Pavilion dv6-1264ca battery.[53]HistoryDiscovery and useMain article: Timeline of hydrogen technologiesIn 1671, Robert Boyle discovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas.[54][55] In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by naming the gas from a metal-acid reaction "flammable air"HP Pavilion dv6-1263cl battery. He speculated that "flammable air" was in fact identical to the hypothetical substance called "phlogiston"[56][57] and further finding in 1781 that the gas produces water when burned. He is usually given credit for its discovery as an element.[58][59] In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὕδρω hydro meaning water and γενῆς genes meaning creator) HP Pavilion dv6-1261tx battery when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned.[59]Antoine-Laurent de LavoisierLavoisier produced hydrogen for his famous experiments on mass conservation by reacting a flux of steam with metallic iron through an incandescent iron tube heated in a fire. Anaerobic oxidation of iron by the protons of water at high temperature can be schematically represented by the set of following reactionsHP Pavilion dv6-1260tx battery: Fe + H2O → FeO + H22 Fe + 3 H2O → Fe2O3 + 3 H23 Fe + 4 H2O → Fe3O4 + 4 H2Many metals such as zirconium undergo a similar reaction with water leading to the production of hydrogen.Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask.[59] He produced solid hydrogen the next year.[59] Deuterium was discovered in December 1931 by Harold UreyHP Pavilion dv6-1260sn battery, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck.[58] Heavy water, which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932.[59] François Isaac de Rivaz built the first internal combustion engine powered by a mixture of hydrogen and oxygen in 1806. Edward Daniel Clarke invented the hydrogen gas blowpipe in 1819HP Pavilion dv6-1260sh battery. The Döbereiner's lamp and limelight were invented in 1823.[59]The first hydrogen-filled balloon was invented by Jacques Charles in 1783.[59] Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard.[59] German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were called ZeppelinsHP Pavilion dv6-1260sg battery; the first of which had its maiden flight in 1900.[59] Regularly scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships were used as observation platforms and bombers during the warHP Pavilion dv6-1260se battery.The first non-stop transatlantic crossing was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States promised increased safety, but the U.S. government refused to sell the gas for this purpose. Therefore, H2 was used in the Hindenburg airship, which was destroyed in a midair fire over New Jersey on May 6, 1937HP Pavilion dv6-1260ev battery.[59] The incident was broadcast live on radio and filmed. Ignition of leaking hydrogen is widely assumed to be the cause, but later investigations pointed to the ignition of the aluminized fabric coating by static electricity. But the damage to hydrogen's reputation as a lifting gas was already doneHP Pavilion dv6-1260et battery.In the same year the first hydrogen-cooled turbogenerator went into service with gaseous hydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, by the Dayton Power & Light Co,[61] because of the thermal conductivity of hydrogen gas this is the most common type in its field todayHP Pavilion dv6-1260ep battery.The nickel hydrogen battery was used for the first time in 1977 aboard the U.S. Navy's Navigation technology satellite-2 (NTS-2).[62] For example, the ISS,[63] Mars Odyssey[64] and the Mars Global Surveyor[65] are equipped with nickel-hydrogen batteries. In the dark part of its orbit, the Hubble Space Telescope is also powered by nickel-hydrogen batteriesHP Pavilion dv6-1260ej battery, which were finally replaced in May 2009, more than 19 years after launch, and 13 years over their design life.Role in quantum theoryHydrogen emission spectrum lines in the visible range. These are the four visible lines of the Balmer seriesBecause of its relatively simple atomic structure, consisting only of a proton and an electron, the hydrogen atom, together with the spectrum of light produced from it or absorbed by it, has been central to the development of the theory of atomic structureHP Pavilion dv6-1260ei battery.[66] Furthermore, the corresponding simplicity of the hydrogen molecule and the corresponding cation H2+ allowed fuller understanding of the nature of the chemical bond, which followed shortly after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.One of the first quantum effects to be explicitly noticed (but not understood at the time) was a Maxwell observation involving hydrogenHP Pavilion dv6-1260ec battery, half a century before full quantum mechanical theory arrived. Maxwell observed that the specific heat capacity of H2 unaccountably departs from that of a diatomic gas below room temperature and begins to increasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theoryHP Pavilion dv6-1259tx battery, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in H2 because of its low mass. These widely spaced levels inhibit equal partition of heat energy into rotational motion in hydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levels and do not exhibit the same effect. HP Pavilion dv6-1259dx batteryNatural occurrenceNGC 604, a giant region of ionized hydrogen in the Triangulum GalaxyHydrogen, as atomic H, is the most abundant chemical element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms (most of the mass of the universe, however, is not in the form of chemical-element type matter, but rather is postulated to occur as yet-undetected forms of mass such as dark matter and dark energy). HP Pavilion dv6-1256tx battery This element is found in great abundance in stars and gas giant planets. Molecular clouds of H2 are associated with star formation. Hydrogen plays a vital role in powering stars through proton-proton reaction and CNO cycle nuclear fusion.[69]Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogenHP Pavilion dv6-1255tx battery. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the Sun and other stars). The charged particles are highly influenced by magnetic and electric fields. For example, in the solar wind they interact with the Earth's magnetosphere giving rise to Birkeland currents and the auroraHP Pavilion dv6-1255eg battery. Hydrogen is found in the neutral atomic state in the Interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4.[70]Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H2 (for data see table) HP Pavilion dv6-1255ee battery. However, hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface,[71] mostly in the form of chemical compounds such as hydrocarbons and waterHP Pavilion dv6-1254tx battery.[37] Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus, as is methane, itself a hydrogen source of increasing importance.[72]A molecular form called protonated molecular hydrogen (H3+) is found in the interstellar medium (ISM), where it is generated by ionization of molecular hydrogen from cosmic raysHP Pavilion dv6-1253cl battery. It has also been observed in the upper atmosphere of the planet Jupiter. This ion is relatively stable in the environment of outer space due to the low temperature and density. H3+ is one of the most abundant ions in the Universe, and it plays a notable role in the chemistry of the interstellar medium.[73] Neutral triatomic hydrogen H3 can only exist in an excited form and is unstableHP Pavilion dv6-1253ca battery.[74] The hydrogen molecular ion (H2+) is a rare molecular system in the universe.ProductionFor more details on this topic, see Hydrogen production.H2 is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the hydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemical reactions.LaboratoryIn the laboratory, H2 is usually prepared by the reaction of acids on metals such as zinc with Kipp's apparatusHP Pavilion dv6-1252tx battery.Zn + 2 H+ → Zn2+ + H2Aluminium can also produce H2 upon treatment with bases:2 Al + 6 H2O + 2 OH− → 2 Al(OH)−4 + 3 H2The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water, and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, howeverHP Pavilion dv6-1250us battery, the gas is to be burnt on site, oxygen is desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, for instance, would oxidize, and thus decrease the amount of oxygen given off.) The theoretical maximum efficiency (electricity used vs. energetic value of hydrogen produced) is in the range 80–94%.[75]2 H2O(l) → 2 H2(g) + O2(g) HP Pavilion dv6-1250ss batteryIn 2007, it was discovered that an alloy of aluminium and gallium in pellet form added to water could be used to generate hydrogen. The process also creates alumina, but the expensive gallium, which prevents the formation of an oxide skin on the pellets, can be re-used. This has important potential implications for a hydrogen economy, as hydrogen can be produced on-site and does not need to be transportedHP Pavilion dv6-1250sp battery.[76]IndustrialMain article: Hydrogen productionHydrogen can be prepared in several different ways, but economically the most important processes involve removal of hydrogen from hydrocarbons. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas.[77] At high temperatures (1000–1400 K, 700–1100 °C or 1300–2000 °F), steam (water vapor) reacts with methane to yield carbon monoxide and H2HP Pavilion dv6-1250sn battery.CH4 + H2O → CO + 3 H2This reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0 MPa, 20 atm or 600 inHg). This is because high-pressure H2 is the most marketable product and Pressure Swing Adsorption (PSA) purification systems work better at higher pressuresHP Pavilion dv6-1250sc battery. The product mixture is known as "synthesis gas" because it is often used directly for the production of methanol and related compounds. Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. One of the many complications to this highly optimized technology is the formation of coke or carbonHP Pavilion dv6-1250eq battery:CH4 → C + 2 H2Consequently, steam reforming typically employs an excess of H2O. Additional hydrogen can be recovered from the steam by use of carbon monoxide through the water gas shift reaction, especially with an iron oxide catalyst. This reaction is also a common industrial source of carbon dioxide:[77]CO + H2O → CO2 + H2Other important methods for H2 production include partial oxidation of hydrocarbons: HP Pavilion dv6-1250ep battery2 CH4 + O2 → 2 CO + 4 H2and the coal reaction, which can serve as a prelude to the shift reaction above:[77]C + H2O → CO + H2Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the Haber process for the production of ammonia, hydrogen is generated from natural gas.[79] Electrolysis of brine to yield chlorine also produces hydrogen as a co-product. HP Pavilion dv6-1250eo batteryThermochemicalThere are more than 200 thermochemical cycles which can be used for water splitting, around a dozen of these cycles such as the iron oxide cycle, cerium(IV) oxide-cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodine cycle, copper-chlorine cycle and hybrid sulfur cycle are under research and in testing phase to produce hydrogen and oxygen from water and heat without using electricityHP Pavilion dv6-1250el battery.[81] A number of laboratories (including in France, Germany, Greece, Japan, and the USA) are developing thermochemical methods to produce hydrogen from solar energy and water.[82]Anaerobic corrosionUnder anaerobic conditions, iron and steel alloys are slowly oxidized by the protons of water concomitantly reduced in molecular hydrogen (H2). The anaerobic corrosion of iron leads first to the formation of ferrous hydroxide (green rust) and can be described by the following reactionHP Pavilion dv6-1250eg battery:Fe + 2 H2O → Fe(OH)2 + H2In its turn, under anaerobic conditions, the ferrous hydroxide (Fe(OH)2 ) can be oxidized by the protons of water to form magnetite and molecular hydrogen. This process is described by the Schikorr reaction:3 Fe(OH)2 → Fe3O4 + 2 H2O + H2ferrous hydroxide → magnetite + water + hydrogenThe well crystallized magnetite (Fe3O4) is thermodynamically more stable than the ferrous hydroxide (Fe(OH)2 ) HP Pavilion dv6-1250eb battery.This process occurs during the anaerobic corrosion of iron and steel in oxygen-free groundwater and in reducing soils below the water table.Geological occurrence: the serpentinization reactionIn the absence of atmospheric oxygen (O2), in deep geological conditions prevailing far away from Earth atmosphere, hydrogen (H2) is produced during the process of serpentinization by the anaerobic oxidation by the water protons HP Pavilion dv6-1249tx battery (H+) of the ferrous (Fe2+) silicate present in the crystal lattice of the fayalite (Fe2SiO4, the olivine iron-endmember). The corresponding reaction leading to the formation of magnetite (Fe3O4), quartz (SiO2) and hydrogen (H2) is the following:3 Fe2SiO4 + 2 H2O → 2 Fe3O4 + 3 SiO2 + 3 H2fayalite + water → magnetite + quartz + hydrogenThis reaction closely resembles the Schikorr reaction observed in the anaerobic oxidation of the ferrous hydroxide in contact with waterHP Pavilion dv6-1249eo battery.ApplicationsConsumption in processesLarge quantities of H2 are needed in the petroleum and chemical industries. The largest application of H2 is for the processing ("upgrading") of fossil fuels, and in the production of ammonia. The key consumers of H2 in the petrochemical plant include hydrodealkylation, hydrodesulfurization, and hydrocrackingHP Pavilion dv6-1248eo battery. H2 has several other important uses. H2 is used as a hydrogenating agent, particularly in increasing the level of saturation of unsaturated fats and oils (found in items such as margarine), and in the production of methanol. It is similarly the source of hydrogen in the manufacture of hydrochloric acid. H2 is also used as a reducing agent of metallic oresHP Pavilion dv6-1248ca battery.[83]Hydrogen is highly soluble in many rare earth and transition metals[84] and is soluble in both nanocrystalline and amorphous metals.[85] Hydrogen solubility in metals is influenced by local distortions or impurities in the crystal lattice.[86] These properties may be useful when hydrogen is purified by passage through hot palladium disksHP Pavilion dv6-1247tx battery, but the gas's high solubility is a metallurgical problem, contributing to the embrittlement of many metals,[8] complicating the design of pipelines and storage tanks.[9]Apart from its use as a reactant, H2 has wide applications in physics and engineering. It is used as a shielding gas in welding methods such as atomic hydrogen weldingHP Pavilion dv6-1247ez battery.[87][88] H2 is used as the rotor coolant in electrical generators at power stations, because it has the highest thermal conductivity of any gas. Liquid H2 is used in cryogenic research, including superconductivity studies.[89] Because H2 is lighter than air, having a little more than 1⁄15 of the density of air, it was once widely used as a lifting gas in balloons and airshipsHP Pavilion dv6-1247et battery.[90]In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industriesHP Pavilion dv6-1247eo battery.[91] Hydrogen is an authorized food additive (E 949) that allows food package leak testing among other anti-oxidizing properties.[92]Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions.[59] Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effectsHP Pavilion dv6-1247cl battery.[93] Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs,[94] as an isotopic label in the biosciences,[51] and as a radiation source in luminous paints.[95]The triple point temperature of equilibrium hydrogen is a defining fixed point on the ITS-90 temperature scale at 13.8033 kelvinsHP Pavilion dv6-1246tx battery.[96]CoolantHydrogen is commonly used in power stations, as a coolant in generators, due to its specific heat capacity being considerably higher than any other gas.Energy carrierSee also: Hydrogen economy and Hydrogen infrastructureHydrogen is not an energy resource,[97] except in the hypothetical context of commercial nuclear fusion power plants using deuterium or tritium, a technology presently far from developmentHP Pavilion dv6-1246eo battery.[98] The Sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve controllably on Earth.[99] Elemental hydrogen from solar, biological, or electrical sources require more energy to make it than is obtained by burning it, so in these cases hydrogen functions as an energy carrier, like a batteryHP Pavilion dv6-1245et battery. Hydrogen may be obtained from fossil sources (such as methane), but these sources are unsustainable.[97]The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass is higher.[97] Nevertheless, elemental hydrogen has been widely discussed in the context of energyHP Pavilion dv6-1245es battery, as a possible future carrier of energy on an economy-wide scale.[100] For example, CO2 sequestration followed by carbon capture and storage could be conducted at the point of H2 production from fossil fuels.[101] Hydrogen used in transportation would burn relatively cleanly, with some NOx emissions,[102] but without carbon emissionsHP Pavilion dv6-1245eo battery.[101] However, the infrastructure costs associated with full conversion to a hydrogen economy would be substantial.[103]Semiconductor industryHydrogen is employed to saturate broken ("dangling") bonds of amorphous silicon and amorphous carbon that helps stabilizing material properties.[104] It is also a potential electron donor in various oxide materials, including ZnO,[105][106] SnO2, CdO, MgO,[107] ZrO2, HfO2, La2O3, Y2O3, TiO2, SrTiO3, LaAlO3, SiO2, Al2O3, ZrSiO4, HfSiO4, and SrZrO3HP Pavilion dv6-1245dx battery.[108]Biological reactionsFurther information: Biohydrogen and Biological hydrogen productionH2 is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually via reactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze the reversible redox reaction between H2 and its component two protons and two electronsHP Pavilion dv6-1244tx battery. Creation of hydrogen gas occurs in the transfer of reducing equivalents produced during pyruvate fermentation to water.[109]Water splitting, in which water is decomposed into its component protons, electrons, and oxygen, occurs in the light reactions in all photosynthetic organisms. Some such organisms, including the alga Chlamydomonas reinhardtii and cyanobacteriaHP Pavilion dv6-1244sb battery, have evolved a second step in the dark reactions in which protons and electrons are reduced to form H2 gas by specialized hydrogenases in the chloroplast.[110] Efforts have been undertaken to genetically modify cyanobacterial hydrogenases to efficiently synthesize H2 gas even in the presence of oxygen.[111] Efforts have also been undertaken with genetically modified alga in a bioreactorHP Pavilion dv6-1243cl battery.[112]Safety and precautionsMain article: Hydrogen safetyHydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxiant in its pure, oxygen-free form.[113] In addition, liquid hydrogen is a cryogen and presents dangers (such as frostbite) associated with very cold liquidsHP Pavilion dv6-1242tx battery.[114] Hydrogen dissolves in many metals, and, in addition to leaking out, may have adverse effects on them, such as hydrogen embrittlement,[115] leading to cracks and explosions.[116] Hydrogen gas leaking into external air may spontaneously ignite. Moreover, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burnsHP Pavilion dv6-1242et battery.[117]Even interpreting the hydrogen data (including safety data) is confounded by a number of phenomena. Many physical and chemical properties of hydrogen depend on the parahydrogen/orthohydrogen ratio (it often takes days or weeks at a given temperature to reach the equilibrium ratio, for which the data is usually given) HP Pavilion dv6-1241et battery. Hydrogen detonation parameters, such as critical detonation pressure and temperature, strongly depend on the container geometry.[113]Oxygen ( /ˈɒksɨdʒɨn/ ok-si-jin) is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς (oxys) ("acid", literally "sharp", referring to the sour taste of acids) and -γενής (-genēs) ("producer", literally "begetter")HP Pavilion dv6-1241eo battery, because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a very pale blue, odorless, tasteless diatomic gas with the formula O2HP Pavilion dv6-1240us battery.Oxygen is a member of the chalcogen group on the periodic table and is a highly reactive nonmetallic element that readily forms compounds (notably oxides) with almost all other elements. Oxygen is a strong oxidizing agent and has the second-highest electronegativity of all the elements (only fluorine has a higher electronegativity) HP Pavilion dv6-1240tx battery.[1] By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium[2] and the most abundant element by mass in the Earth's crust, making up almost half of the crust's mass.[3] Free oxygen is too chemically reactive to appear on Earth without the photosynthetic action of living organisms, which use the energy of sunlight to produce elemental oxygen from waterHP Pavilion dv6-1240sh battery. Elemental O2 only began to accumulate in the atmosphere after the evolutionary appearance of these organisms, roughly 2.5 billion years ago.[4] Diatomic oxygen gas constitutes 20.8% of the volume of air.[5]Because it comprises most of the mass in water, oxygen comprises most of the mass of living organisms (for example, about two-thirds of the human body's mass). All major classes of structural molecules in living organisms, such as proteinsHP Pavilion dv6-1240sf battery, carbohydrates, and fats, contain oxygen, as do the major inorganic compounds that comprise animal shells, teeth, and bone. Elemental oxygen is produced by cyanobacteria, algae and plants, and is used in cellular respiration for all complex life. Oxygen is toxic to obligately anaerobic organisms, which were the dominant form of early life on Earth until O2 began to accumulate in the atmosphereHP Pavilion dv6-1240sb battery. Another form (allotrope) of oxygen, ozone (O3), helps protect the biosphere from ultraviolet radiation with the high-altitude ozone layer, but is a pollutant near the surface where it is a by-product of smog. At even higher low earth orbit altitudes atomic oxygen is a significant presence and a cause of erosion for spacecraftHP Pavilion dv6-1240ez battery.[6]Oxygen was independently discovered by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774, but Priestley is often given priority because his work was published first. The name oxygen was coined in 1777 by Antoine Lavoisier,[7] whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosionHP Pavilion dv6-1240ep battery. Oxygen is produced industrially by fractional distillation of liquefied air, use of zeolites with pressure-cycling to concentrate oxygen from air, electrolysis of water and other means. Uses of oxygen include the production of steel, plastics and textiles; rocket propellant; oxygen therapy; and life support in aircraft, submarines, spaceflight and divingHP Pavilion dv6-1240eo battery.CharacteristicsStructureOxygen discharge (spectrum) tubeAt standard temperature and pressure, oxygen is a very pale blue, odorless gas with the molecular formula O2, in which the two oxygen atoms are chemically bonded to each other with a spin triplet electron configuration. This bond has a bond order of two, and is often simplified in description as a double bond[8] or as a combination of one two-electron bond and two three-electron bondsHP Pavilion dv6-1240el battery.[9]Triplet oxygen (not to be confused with ozone, O3) is the ground state of the O2 molecule.[10] The electron configuration of the molecule has two unpaired electrons occupying two degenerate molecular orbitals.[11] These orbitals are classified as antibonding (weakening the bond order from three to two) HP Pavilion dv6-1240ek battery, so the diatomic oxygen bond is weaker than the diatomic nitrogen triple bond in which all bonding molecular orbitals are filled, but some antibonding orbitals are not.[10]A trickle of liquid oxygen is deflected by a magnetic field, illustrating its paramagnetic propertyIn normal triplet form, O2 molecules are paramagnetic. That is, they form a magnet in the presence of a magnetic field—because of the spin magnetic moments of the unpaired electrons in the moleculeHP Pavilion dv6-1240ei battery, and the negative exchange energy between neighboring O2 molecules.[12] Liquid oxygen is attracted to a magnet to a sufficient extent that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet. HP Pavilion dv6-1240ef batterySinglet oxygen is a name given to several higher-energy species of molecular O2 in which all the electron spins are paired. It is much more reactive towards common organic molecules than is molecular oxygen per se. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlightHP Pavilion dv6-1240ed battery.[15] It is also produced in the troposphere by the photolysis of ozone by light of short wavelength,[16] and by the immune system as a source of active oxygen.[17] Carotenoids in photosynthetic organisms (and possibly also in animals) play a major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissuesHP Pavilion dv6-1240ec battery.[18]AllotropesMain article: Allotropes of oxygenOzone is a rare gas on Earth found mostly in the stratosphere.The common allotrope of elemental oxygen on Earth is called dioxygen, O2. It has a bond length of 121 pm and a bond energy of 498 kJ·mol−1.[19] This is the form that is used by complex forms of life, such as animals, in cellular respiration (see Biological role) and is the form that is a major part of the Earth's atmosphere (see Occurrence) HP Pavilion dv6-1240ea battery. Other aspects of O2 are covered in the remainder of this article.Trioxygen (O3) is usually known as ozone and is a very reactive allotrope of oxygen that is damaging to lung tissue.[20] Ozone is produced in the upper atmosphere when O2 combines with atomic oxygen made by the splitting of O2 by ultraviolet (UV) radiation.[7] Since ozone absorbs strongly in the UV region of the spectrumHP Pavilion dv6-1239tx battery, the ozone layer of the upper atmosphere functions as a protective radiation shield for the planet.[7] Near the Earth's surface, however, it is a pollutant formed as a by-product of automobile exhaust.[20] The metastable molecule tetraoxygen (O4) was discovered in 2001,[21][22] and was assumed to exist in one of the six phases of solid oxygenHP Pavilion dv6-1239et battery. It was proven in 2006 that this phase, created by pressurizing O2 to 20 GPa, is in fact a rhombohedral O8 cluster.[23] This cluster has the potential to be a much more powerful oxidizer than either O2 or O3 and may therefore be used in rocket fuel.[21][22] A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa[24] and it was shown in 1998 that at very low temperatures, this phase becomes superconducting. HP Pavilion dv6-1239es batteryPhysical propertiesSee also: Liquid oxygen and solid oxygenOxygen is more soluble in water than nitrogen is; water contains approximately 1 molecule of O2 for every 2 molecules of N2, compared to an atmospheric ratio of approximately 1:4. The solubility of oxygen in water is temperature-dependent, and about twice as much (14.6 mg·L−1) dissolves at 0 °C than at 20 °C (7.6 mg·L−1). HP Pavilion dv6-1238nr battery At 25 °C and 1 standard atmosphere (101.3 kPa) of air, freshwater contains about 6.04 milliliters (mL) of oxygen per liter, whereas seawater contains about 4.95 mL per liter.[28] At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for water and 7.2 mL (45% more) per liter for sea water.Oxygen condenses at 90.20 K (−182.95 °C, −297.31 °F) HP Pavilion dv6-1238et battery, and freezes at 54.36 K (−218.79 °C, −361.82 °F).[29] Both liquid and solid O2 are clear substances with a light sky-blue color caused by absorption in the red (in contrast with the blue color of the sky, which is due to Rayleigh scattering of blue light). High-purity liquid O2 is usually obtained by the fractional distillation of liquefied airHP Pavilion dv6-1238es battery.[30] Liquid oxygen may also be produced by condensation out of air, using liquid nitrogen as a coolant. It is a highly reactive substance and must be segregated from combustible materials.[31]Isotopes and stellar originMain article: Isotopes of oxygenLate in a massive star's life, 16O concentrates in the O-shell, 17O in the H-shell and oxygen-1818O in the He-shell.Naturally occurring oxygen is composed of three stable isotopes, 16O, 17O, and 18O, with 16O being the most abundant (99.762% natural abundance) HP Pavilion dv6-1238ca battery.[32]Most 16O is synthesized at the end of the helium fusion process in massive stars but some is made in the neon burning process.[33] 17O is primarily made by the burning of hydrogen into helium during the CNO cycle, making it a common isotope in the hydrogen burning zones of stars.[33] Most 18O is produced when 14NHP Pavilion dv6-1237et battery (made abundant from CNO burning) captures a 4He nucleus, making 18O common in the helium-rich zones of evolved, massive stars.[33]Fourteen radioisotopes have been characterized. The most stable are 15O with a half-life of 122.24 seconds and 14O with a half-life of 70.606 seconds.[32] All of the remaining radioactive isotopes have half-lives that are less than 27 s and the majority of these have half-lives that are less than 83 millisecondsHP Pavilion dv6-1237es battery.[32] The most common decay mode of the isotopes lighter than 16O is β+ decay[34][35][36] to yield nitrogen, and the most common mode for the isotopes heavier than 18O is beta decay to yield fluorine.[32]OccurrenceOxygen is the most abundant chemical element, by mass, in our biosphere, air, sea and land. Oxygen is the third most abundant chemical element in the universe, after hydrogen and helium.[2] About 0.9% of the Sun's mass is oxygenHP Pavilion dv6-1237ca battery.[5] Oxygen constitutes 49.2% of the Earth's crust by mass[3] and is the major component of the world's oceans (88.8% by mass).[5] Oxygen gas is the second most common component of the Earth's atmosphere, taking up 20.8% of its volume and 23.1% of its mass (some 1015 tonnes). Earth is unusual among the planets of the Solar System in having such a high concentration of oxygen gas in its atmosphere: Mars (with 0.1% O2 by volume) HP Pavilion dv6-1236ss battery and Venus have far lower concentrations. However, the O2 surrounding these other planets is produced solely by ultraviolet radiation impacting oxygen-containing molecules such as carbon dioxide.The unusually high concentration of oxygen gas on Earth is the result of the oxygen cycle. This biogeochemical cycle describes the movement of oxygen within and between its three main reservoirs on EarthHP Pavilion dv6-1236et battery: the atmosphere, the biosphere, and the lithosphere. The main driving factor of the oxygen cycle is photosynthesis, which is responsible for modern Earth's atmosphere. Photosynthesis releases oxygen into the atmosphere, while respiration and decay remove it from the atmosphere. In the present equilibrium, production and consumption occur at the same rate of roughly 1/2000th of the entire atmospheric oxygen per yearHP Pavilion dv6-1236eo battery.Cold water holds more dissolved O2.Free oxygen also occurs in solution in the world's water bodies. The increased solubility of O2 at lower temperatures (see Physical properties) has important implications for ocean life, as polar oceans support a much higher density of life due to their higher oxygen content.[40] Polluted water may have reduced amounts of O2 in itHP Pavilion dv6-1235ss battery, depleted by decaying algae and other biomaterials through a process called eutrophication. Scientists assess this aspect of water quality by measuring the water's biochemical oxygen demand, or the amount of O2 needed to restore it to a normal concentration. HP Pavilion dv6-1235sb batteryBiological roleMain article: Dioxygen in biological reactionsPhotosynthesis and respirationPhotosynthesis splits water to liberate O2 and fixes CO2 into sugar.In nature, free oxygen is produced by the light-driven splitting of water during oxygenic photosynthesis. According to some estimates, Green algae and cyanobacteria in marine environments provide about 70% of the free oxygen produced on earth and the rest is produced by terrestrial plants. HP Pavilion dv6-1235et battery Other estimates of the oceanic contribution to atmospheric oxygen are higher, while some estimates are lower, suggesting oceans produce ~45% of Earth's atmospheric oxygen each year.[43]A simplified overall formula for photosynthesis is:[44]6 CO2 + 6 H2O + photons → C6H12O6 + 6 O2 (or simply carbon dioxide + water + sunlight → glucose + dioxygen) HP Pavilion dv6-1235es batteryPhotolytic oxygen evolution occurs in the thylakoid membranes of photosynthetic organisms and requires the energy of four photons.[45] Many steps are involved, but the result is the formation of a proton gradient across the thylakoid membrane, which is used to synthesize ATP via photophosphorylation.[46] The O2 remaining after oxidation of the water molecule is released into the atmosphere. HP Pavilion dv6-1235eo batteryMolecular dioxygen, O2, is essential for cellular respiration in all aerobic organisms. Oxygen is used in mitochondria to help generate adenosine triphosphate (ATP) during oxidative phosphorylation. The reaction for aerobic respiration is essentially the reverse of photosynthesis and is simplified asHP Pavilion dv6-1235ee battery:C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 2880 kJ·mol−1In vertebrates, O2 diffuses through membranes in the lungs and into red blood cells. Hemoglobin binds O2, changing its color from bluish red to bright red[20] (CO2 is released from another part of hemoglobin through the Bohr effect). Other animals use hemocyanin (molluscs and some arthropods) or hemerythrin (spiders and lobsters).[38] A liter of blood can dissolve 200 cm3 of O2. HP Pavilion dv6-1235ec batteryReactive oxygen species, such as superoxide ion (O−2) and hydrogen peroxide (H2O2), are dangerous by-products of oxygen use in organisms.[38] Parts of the immune system of higher organisms, however, create peroxide, superoxide, and singlet oxygen to destroy invading microbes. Reactive oxygen species also play an important role in the hypersensitive response of plants against pathogen attack. HP Pavilion dv6-1234tx batteryAn adult human in rest inhales 1.8 to 2.4 grams of oxygen per minute.[48] This amounts to more than 6 billion tonnes of oxygen inhaled by humanity per year.[49]Content in bodyThe oxygen content in the body of a living organism is usually highest in the respiratory system, and decreases along any arterial system, peripheral tissues and venous system, respectivelyHP Pavilion dv6-1234nr battery. Oxygen content in this sense is often given as the partial pressure, which is the pressure which oxygen would have if it alone occupied the volume.[53]Build-up in the atmosphereFree oxygen gas was almost nonexistent in Earth's atmosphere before photosynthetic archaea and bacteria evolved. Free oxygen first appeared in significant quantities during the Paleoproterozoic eon (between 2.5 and 1.6 billion years ago). At first, the oxygen combined with dissolved iron in the oceans to form banded iron formationsHP Pavilion dv6-1234eo battery. Free oxygen started to outgas from the oceans 2.7 billion years ago, reaching 10% of its present level around 1.7 billion years ago.[54]The presence of large amounts of dissolved and free oxygen in the oceans and atmosphere may have driven most of the anaerobic organisms then living to extinction during the Great Oxygenation Event(oxygen catastrophe) about 2.4 billion years agoHP Pavilion dv6-1233et battery. However, cellular respiration using O2 enables aerobic organisms to produce much more ATP than anaerobic organisms, helping the former to dominate Earth's biosphere.[55] Photosynthesis and cellular respiration of O2 allowed for the evolution of eukaryotic cells and ultimately complex multicellular organisms such as plants and animalsHP Pavilion dv6-1233eo battery.Since the beginning of the Cambrian period 540 million years ago, O2 levels have fluctuated between 15% and 30% by volume.[56] Towards the end of the Carboniferous period (about 300 million years ago) atmospheric O2 levels reached a maximum of 35% by volumeHP Pavilion dv6-1232ss battery,[56] which may have contributed to the large size of insects and amphibians at this time.[57] Human activities, including the burning of 7 billion tonnes of fossil fuels each year have had very little effect on the amount of free oxygen in the atmosphere.[12] At the current rate of photosynthesis it would take about 2,000 years to regenerate the entire O2 in the present atmosphereHP Pavilion dv6-1232et battery.[58]HistoryEarly experimentsPhilo's experiment inspired later investigators.One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neckHP Pavilion dv6-1232eo battery.[59] Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respirationHP Pavilion dv6-1231eo battery.[60]In the late 17th century, Robert Boyle proved that air is necessary for combustion. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus or just nitroaereus.[61] In one experiment he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjectsHP Pavilion dv6-1230us battery.[62] From this he surmised that nitroaereus is consumed in both respiration and combustion.Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it.[61] He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the bodyHP Pavilion dv6-1230ss battery.[61] Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione".[62]Phlogiston theoryMain article: Phlogiston theoryStahl helped develop and popularize the phlogiston theory.Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as an element.[26] This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processesHP Pavilion dv6-1230sl battery.Established in 1667 by the German alchemist J. J. Becher, and modified by the chemist Georg Ernst Stahl by 1731,[63] phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calxHP Pavilion dv6-1230sf battery.[60]Highly combustible materials that leave little residue, such as wood or coal, were thought to be made mostly of phlogiston; whereas non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the ideaHP Pavilion dv6-1230sb battery; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process.[60] The fact that a substance like wood actually gains overall weight in burning was hidden by the buoyancy of the gaseous combustion products. Indeed one of the first clues that the phlogiston theory was incorrect was that metalsHP Pavilion dv6-1230ew battery, too, gain weight in rusting (when they were supposedly losing phlogiston).DiscoveryCarl Wilhelm Scheele beat Priestley to the discovery but published afterwards.Oxygen was first discovered by Swedish pharmacist Carl Wilhelm Scheele. He had produced oxygen gas by heating mercuric oxide and various nitrates by about 1772.[5][60] Scheele called the gas "fire air" because it was the only known supporter of combustionHP Pavilion dv6-1230et battery, and wrote an account of this discovery in a manuscript he titled Treatise on Air and Fire, which he sent to his publisher in 1775. However, that document was not published until 1777.[64]Joseph Priestley is usually given priority in the discovery.In the meantime, on August 1, 1774, an experiment conducted by the British clergyman Joseph Priestley focused sunlight on mercuric oxide (HgO) inside a glass tube, which liberated a gas he named "dephlogisticated air"HP Pavilion dv6-1230er battery.[5] He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, he wrote: "The feeling of it to my lungs was not sensibly different from that of common air, but I fancied that my breast felt peculiarly light and easy for some time afterwards." HP Pavilion dv6-1230eq battery Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air" which was included in the second volume of his book titled Experiments and Observations on Different Kinds of Air.[60][65] Because he published his findings first, Priestley is usually given priority in the discoveryHP Pavilion dv6-1230eo battery.The noted French chemist Antoine Laurent Lavoisier later claimed to have discovered the new substance independently. However, Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele also posted a letter to Lavoisier on September 30, 1774 that described his own discovery of the previously unknown substanceHP Pavilion dv6-1230ek battery, but Lavoisier never acknowledged receiving it (a copy of the letter was found in Scheele's belongings after his death).[64]Lavoisier's contributionWhat Lavoisier did indisputably do (although this was disputed at the time) was to conduct the first adequate quantitative experiments on oxidation and give the first correct explanation of how combustion worksHP Pavilion dv6-1230ej battery.[5] He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a chemical element.Antoine Lavoisier discredited the Phlogiston theory.In one experiment, Lavoisier observed that there was no overall increase in weight when tin and air were heated in a closed containerHP Pavilion dv6-1230ed battery.[5] He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book Sur la combustion en général, which was published in 1777. HP Pavilion dv6-1230ec battery In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and azote (Gk. ἄζωτον "lifeless"), which did not support either. Azote later became nitrogen in English, although it has kept the name in French and several other European languagesHP Pavilion dv6-1230ca battery.[5]Lavoisier renamed 'vital air' to oxygène in 1777 from the Greek roots ὀξύς (oxys) (acid, literally "sharp," from the taste of acids) and -γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids.[7] Chemists (notably Sir Humphrey Davy in 1812) eventually determined that Lavoisier was wrong in this regardHP Pavilion dv6-1229tx battery (it is in fact hydrogen that forms the basis for acid chemistry), but by that time it was too late, the name had taken.Oxygen entered the English language despite opposition by English scientists and the fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book The Botanic Garden (1791) by Erasmus Darwin, grandfather of Charles Darwin. HP Pavilion dv6-1229sf batteryLater historyRobert H. Goddard and a liquid oxygen-gasoline rocketJohn Dalton's original atomic hypothesis assumed that all elements were monoatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula was HO, giving the atomic mass of oxygen as 8 times that of hydrogen, instead of the modern value of about 16HP Pavilion dv6-1229et battery.[66] In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811 Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called Avogadro's law and the assumption of diatomic elemental molecules. HP Pavilion dv6-1229er batteryBy the late 19th century scientists realized that air could be liquefied, and its components isolated, by compressing and cooling it. Using a cascade method, Swiss chemist and physicist Raoul Pierre Pictet evaporated liquid sulfur dioxide in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy itHP Pavilion dv6-1228tx battery. He sent a telegram on December 22, 1877 to the French Academy of Sciences in Paris announcing his discovery of liquid oxygen.[69] Just two days later, French physicist Louis Paul Cailletet announced his own method of liquefying molecular oxygen.[69] Only a few drops of the liquid were produced in either case so no meaningful analysis could be conductedHP Pavilion dv6-1228sf battery. Oxygen was liquified in stable state for the first time on March 29, 1883 by Polish scientists from Jagiellonian University, Zygmunt Wróblewski and Karol Olszewski.[70]In 1891 Scottish chemist James Dewar was able to produce enough liquid oxygen to study.[12] The first commercially viable process for producing liquid oxygen was independently developed in 1895 by German engineer Carl von Linde and British engineer William HampsonHP Pavilion dv6-1228ez battery. Both men lowered the temperature of air until it liquefied and then distilled the component gases by boiling them off one at a time and capturing them.[71] Later, in 1901, oxyacetylene welding was demonstrated for the first time by burning a mixture of acetylene and compressed O2. This method of welding and cutting metal later became commonHP Pavilion dv6-1227sf battery.[71]In 1923 the American scientist Robert H. Goddard became the first person to develop a rocket engine; the engine used gasoline for fuel and liquid oxygen as the oxidizer. Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926 in Auburn, Massachusetts, USA. HP Pavilion dv6-1225tx batteryIndustrial productionSee also: Air separation, Oxygen evolution, and fractional distillationTwo major methods are employed to produce 100 million tonnes of O2 extracted from air for industrial uses annually.[64] The most common method is to fractionally distill liquefied air into its various components, with N2 distilling as a vapor while O2 is left as a liquid. HP Pavilion dv6-1225sv batteryHofmann electrolysis apparatus used in electrolysis of water.The other major method of producing O2 gas involves passing a stream of clean, dry air through one bed of a pair of identical zeolite molecular sieves, which absorbs the nitrogen and delivers a gas stream that is 90% to 93% O2.[64] Simultaneously, nitrogen gas is released from the other nitrogen-saturated zeolite bed, by reducing the chamber operating pressure and diverting part of the oxygen gas from the producer bed through it, in the reverse direction of flowHP Pavilion dv6-1225ss battery. After a set cycle time the operation of the two beds is interchanged, thereby allowing for a continuous supply of gaseous oxygen to be pumped through a pipeline. This is known as pressure swing adsorption. Oxygen gas is increasingly obtained by these non-cryogenic technologies (see also the related vacuum swing adsorption). HP Pavilion dv6-1225so batteryOxygen gas can also be produced through electrolysis of water into molecular oxygen and hydrogen. DC electricity must be used: if AC is used, the gases in each limb consist of hydrogen and oxygen in the explosive ratio 2:1. Contrary to popular belief, the 2:1 ratio observed in the DC electrolysis of acidified water does not prove that the empirical formula of water is H2O unless certain assumptions are made about the molecular formulae of hydrogen and oxygen themselvesHP Pavilion dv6-1225sf battery. A similar method is the electrocatalytic O2 evolution from oxides and oxoacids. Chemical catalysts can be used as well, such as in chemical oxygen generators or oxygen candles that are used as part of the life-support equipment on submarines, and are still part of standard equipment on commercial airliners in case of depressurization emergenciesHP Pavilion dv6-1225ew battery. Another air separation technology involves forcing air to dissolve through ceramic membranes based on zirconium dioxide by either high pressure or an electric current, to produce nearly pure O2 gas.[41]In large quantities, the price of liquid oxygen in 2001 was approximately $0.21/kg.[74] Since the primary cost of production is the energy cost of liquefying the air, the production cost will change as energy cost variesHP Pavilion dv6-1225et battery.For reasons of economy, oxygen is often transported in bulk as a liquid in specially insulated tankers, since one litre of liquefied oxygen is equivalent to 840 liters of gaseous oxygen at atmospheric pressure and 20 °C (68 °F).[64] Such tankers are used to refill bulk liquid oxygen storage containersHP Pavilion dv6-1225er battery, which stand outside hospitals and other institutions with a need for large volumes of pure oxygen gas. Liquid oxygen is passed through heat exchangers, which convert the cryogenic liquid into gas before it enters the building. Oxygen is also stored and shipped in smaller cylinders containing the compressed gas; a form that is useful in certain portable medical applications and oxy-fuel welding and cutting. HP Pavilion dv6-1225ei batteryApplicationsSee also: Breathing gas, Redox, and CombustionMedicalAn oxygen concentrator in an emphysema patient's houseMain article: Oxygen therapyUptake of O2 from the air is the essential purpose of respiration, so oxygen supplementation is used in medicine. Treatment not only increases oxygen levels in the patient's blood, but has the secondary effect of decreasing resistance to blood flow in many types of diseased lungs, easing work load on the heartHP Pavilion dv6-1225ef battery. Oxygen therapy is used to treat emphysema, pneumonia, some heart disorders (congestive heart failure), some disorders that cause increased pulmonary artery pressure, and any disease that impairs the body's ability to take up and use gaseous oxygenHP Pavilion dv6-1225ee battery.[75]Treatments are flexible enough to be used in hospitals, the patient's home, or increasingly by portable devices. Oxygen tents were once commonly used in oxygen supplementation, but have since been replaced mostly by the use of oxygen masks or nasal cannulasHP Pavilion dv6-1224eo battery.[76]Hyperbaric (high-pressure) medicine uses special oxygen chambers to increase the partial pressure of O2 around the patient and, when needed, the medical staff.[77] Carbon monoxide poisoning, gas gangrene, and decompression sickness (the 'bends') are sometimes treated using these devicesHP Pavilion dv6-1223sl battery.[78] Increased O2 concentration in the lungs helps to displace carbon monoxide from the heme group of hemoglobin.[79][80] Oxygen gas is poisonous to the anaerobic bacteria that cause gas gangrene, so increasing its partial pressure helps kill them.[81][82] Decompression sickness occurs in divers who decompress too quickly after a dive, resulting in bubbles of inert gas, mostly nitrogen and helium, forming in their bloodHP Pavilion dv6-1223sf battery. Increasing the pressure of O2 as soon as possible is part of the treatment.Oxygen is also used medically for patients who require mechanical ventilation, often at concentrations above the 21% found in ambient air.Life support and recreational useLow pressure pure O2 is used in space suits.A notable application of O2 as a low-pressure breathing gas is in modern space suits, which surround their occupant's body with pressurized air. These devices use nearly pure oxygen at about one third normal pressure, resulting in a normal blood partial pressure of O2.[85][86] This trade-off of higher oxygen concentration for lower pressure is needed to maintain flexible spacesuitsHP Pavilion dv6-1223eo battery.Scuba divers and submariners also rely on artificially delivered O2, but most often use normal pressure, and/or mixtures of oxygen and air. Pure or nearly pure O2 use in diving at higher-than-sea-level pressures is usually limited to rebreather, decompression, or emergency treatment use at relatively shallow depths (~6 meters depth, or less). HP Pavilion dv6-1222tx battery Deeper diving requires significant dilution of O2 with other gases, such as nitrogen or helium, to help prevent oxygen toxicity.[87]People who climb mountains or fly in non-pressurized fixed-wing aircraft sometimes have supplemental O2 supplies.[89] Passengers traveling in (pressurized) commercial airplanes have an emergency supply of O2 automatically supplied to them in case of cabin depressurizationHP Pavilion dv6-1222sl battery. Sudden cabin pressure loss activates chemical oxygen generators above each seat, causing oxygen masks to drop. Pulling on the masks "to start the flow of oxygen" as cabin safety instructions dictate, forces iron filings into the sodium chlorate inside the canister.[41] A steady stream of oxygen gas is then produced by the exothermic reactionHP Pavilion dv6-1222et battery.Oxygen, as a supposed mild euphoric, has a history of recreational use in oxygen bars and in sports. Oxygen bars are establishments, found in Japan, California, and Las Vegas, Nevada since the late 1990s that offer higher than normal O2 exposure for a fee.[90] Professional athletes, especially in American footballHP Pavilion dv6-1222eo battery, also sometimes go off field between plays to wear oxygen masks in order to get a "boost" in performance. The pharmacological effect is doubtful; a placebo effect is a more likely explanation.[90] Available studies support a performance boost from enriched O2 mixtures only if they are breathed during aerobic exerciseHP Pavilion dv6-1221tx battery.[91]Other recreational uses that do not involve breathing the gas include pyrotechnic applications, such as George Goble's five-second ignition of barbecue grills.[92]IndustrialMost commercially produced O2 is used to smelt iron into steel.Smelting of iron ore into steel consumes 55% of commercially produced oxygen.[41] In this process, O2 is injected through a high-pressure lance into molten iron, which removes sulfur impurities and excess carbon as the respective oxides, SO2 and CO2HP Pavilion dv6-1221sl battery. The reactions are exothermic, so the temperature increases to 1,700 °C.[41]Another 25% of commercially produced oxygen is used by the chemical industry.[41] Ethylene is reacted with O2 to create ethylene oxide, which, in turn, is converted into ethylene glycol; the primary feeder material used to manufacture a host of products, including antifreeze and polyester polymers (the precursors of many plastics and fabrics). HP Pavilion dv6-1221eo batteryMost of the remaining 20% of commercially produced oxygen is used in medical applications, metal cutting and welding, as an oxidizer in rocket fuel, and in water treatment.[41] Oxygen is used in oxyacetylene welding burning acetylene with O2 to produce a very hot flame. In this process, metal up to 60 cm thick is first heated with a small oxy-acetylene flame and then quickly cut by a large stream of O2. HP Pavilion dv6-1221ax battery Larger rockets use liquid oxygen as their oxidizer, which is mixed and ignited with the fuel for propulsion.[citation needed]Scientific500 million years of climate change vs 18OPaleoclimatologists measure the ratio of oxygen-18 and oxygen-16 in the shells and skeletons of marine organisms to determine what the climate was like millions of years ago (see oxygen isotope ratio cycle). Seawater molecules that contain the lighter isotope, oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18HP Pavilion dv6-1220tx battery; this disparity increases at lower temperatures.[94] During periods of lower global temperatures, snow and rain from that evaporated water tends to be higher in oxygen-16, and the seawater left behind tends to be higher in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climateHP Pavilion dv6-1220st battery.[94] Paleoclimatologists also directly measure this ratio in the water molecules of ice core samples that are up to several hundreds of thousands of years old.Planetary geologists have measured different abundances of oxygen isotopes in samples from the Earth, the Moon, Mars, and meteorites, but were long unable to obtain reference values for the isotope ratios in the SunHP Pavilion dv6-1220ss battery, believed to be the same as those of the primordial solar nebula. However, analysis of a silicon wafer exposed to the solar wind in space and returned by the crashed Genesis spacecraft has shown that the Sun has a higher proportion of oxygen-16 than does the EarthHP Pavilion dv6-1220sp battery. The measurement implies that an unknown process depleted oxygen-16 from the Sun's disk of protoplanetary material prior to the coalescence of dust grains that formed the Earth.[95]Oxygen presents two spectrophotometric absorption bands peaking at the wavelengths 687 and 760 nm. Some remote sensing scientists have proposed using the measurement of the radiance coming from vegetation canopies in those bands to characterize plant health status from a satellite platformHP Pavilion dv6-1220so battery.[96] This approach exploits the fact that in those bands it is possible to discriminate the vegetation's reflectance from its fluorescence, which is much weaker. The measurement is technically difficult owing to the low signal-to-noise ratio and the physical structure of vegetation; but it has been proposed as a possible method of monitoring the carbon cycle from satellites on a global scaleHP Pavilion dv6-1220sh battery.CompoundsMain article: Compounds of oxygenWater (H2O) is the most familiar oxygen compound.The oxidation state of oxygen is −2 in almost all known compounds of oxygen. The oxidation state −1 is found in a few compounds such as peroxides.[97] Compounds containing oxygen in other oxidation states are very uncommon: −1/2 (superoxides), −1/3 (ozonides), 0 (elemental, hypofluorous acid), +1/2 (dioxygenyl), +1 (dioxygen difluoride), and +2 (oxygen difluoride) HP Pavilion dv6-1220sd battery.Oxides and other inorganic compoundsWater (H2O) is the oxide of hydrogen and the most familiar oxygen compound. Hydrogen atoms are covalently bonded to oxygen in a water molecule but also have an additional attraction (about 23.3 kJ·mol−1 per hydrogen atom) to an adjacent oxygen atom in a separate molecule. HP Pavilion dv6-1220sb battery These hydrogen bonds between water molecules hold them approximately 15% closer than what would be expected in a simple liquid with just van der Waals forces.[99][100]Oxides, such as iron oxide or rust form when oxygen combines with other elements.Due to its electronegativity, oxygen forms chemical bonds with almost all other elements at elevated temperatures to give corresponding oxides. However, some elements readily form oxides at standard conditions for temperature and pressureHP Pavilion dv6-1220sa battery; the rusting of iron is an example. The surface of metals like aluminium and titanium are oxidized in the presence of air and become coated with a thin film of oxide that passivates the metal and slows further corrosion. Some of the transition metal oxides are found in nature as non-stoichiometric compounds, with a slightly less metal than the chemical formula would showHP Pavilion dv6-1220ez battery. For example, the natural occurring FeO (wüstite) is actually written as Fe1 − xO, where x is usually around 0.05.[101]Oxygen as a compound is present in the atmosphere in trace quantities in the form of carbon dioxide (CO2). The earth's crustal rock is composed in large part of oxides of silicon (silica SiO2, found in granite and sand), aluminium (aluminium oxide Al2O3, in bauxite and corundum), iron (iron(III) oxide Fe2O3HP Pavilion dv6-1220ew battery, in hematite and rust), and calcium carbonate (in limestone). The rest of the Earth's crust is also made of oxygen compounds, in particular various complex silicates (in silicate minerals). The Earth's mantle, of much larger mass than the crust, is largely composed of silicates of magnesium and ironHP Pavilion dv6-1220ev battery.Water-soluble silicates in the form of Na4SiO4, Na2SiO3, and Na2Si2O5 are used as detergents and adhesives.[102]Oxygen also acts as a ligand for transition metals, forming metal–O2 bonds with the iridium atom in Vaska's complex,[103] with the platinum in PtF6,[104] and with the iron center of the heme group of hemoglobin.Organic compounds and biomoleculesAcetone is an important feeder material in the chemical industryHP Pavilion dv6-1220er battery.OxygenCarbonHydrogenOxygen represents more than 40% of the molecular mass of the ATP molecule.Among the most important classes of organic compounds that contain oxygen are (where "R" is an organic group): alcohols (R-OH); ethers (R-O-R); ketones (R-CO-R); aldehydes (R-CO-H); carboxylic acids (R-COOH); esters (R-COO-R); acid anhydrides (R-CO-O-CO-R); and amides (R-C(O)-NR2) HP Pavilion dv6-1220ek battery. There are many important organic solvents that contain oxygen, including: acetone, methanol, ethanol, isopropanol, furan, THF, diethyl ether, dioxane, ethyl acetate, DMF, DMSO, acetic acid, and formic acid. Acetone ((CH3)2CO) and phenol (C6H5OH) are used as feeder materials in the synthesis of many different substancesHP Pavilion dv6-1220ei battery. Other important organic compounds that contain oxygen are: glycerol, formaldehyde, glutaraldehyde, citric acid, acetic anhydride, and acetamide. Epoxides are ethers in which the oxygen atom is part of a ring of three atoms.Oxygen reacts spontaneously with many organic compounds at or below room temperature in a process called autoxidationHP Pavilion dv6-1220eg battery.[105] Most of the organic compounds that contain oxygen are not made by direct action of O2. Organic compounds important in industry and commerce that are made by direct oxidation of a precursor include ethylene oxide and peracetic acid.[102]The element is found in almost all biomolecules that are important to (or generated by) life. Only a few common complex biomolecules, such as squalene and the carotenes, contain no oxygenHP Pavilion dv6-1220ec battery. Of the organic compounds with biological relevance, carbohydrates contain the largest proportion by mass of oxygen. All fats, fatty acids, amino acids, and proteins contain oxygen (due to the presence of carbonyl groups in these acids and their ester residues). Oxygen also occurs in phosphate (PO3−4) groups in the biologically important energy-carrying molecules ATP and ADPHP Pavilion dv6-1219tx battery, in the backbone and the purines (except adenine) and pyrimidines of RNA and DNA, and in bones as calcium phosphate and hydroxylapatite.Safety and precautionsToxicityMain article: Oxygen toxicityMain symptoms of oxygen toxicity[106]Oxygen toxicity occurs when the lungs take in a higher than normal O2 partial pressure, which can occur in deep scuba diving.Oxygen gas (O2) can be toxic at elevated partial pressures, leading to convulsions and other health problems. Oxygen toxicity usually begins to occur at partial pressures more than 50 kilopascals (kPa), or 2.5 times the normal sea-level O2 partial pressure of about 21 kPa (equal to about 50% oxygen composition at standard pressure) HP Pavilion dv6-1219ez battery. This is not a problem except for patients on mechanical ventilators, since gas supplied through oxygen masks in medical applications is typically composed of only 30%–50% O2 by volume (about 30 kPa at standard pressure).[26] (although this figure also is subject to wide variation, depending on type of mask) HP Pavilion dv6-1218tx battery.At one time, premature babies were placed in incubators containing O2-rich air, but this practice was discontinued after some babies were blinded by it.[26][109]Breathing pure O2 in space applications, such as in some modern space suits, or in early spacecraft such as Apollo, causes no damage due to the low total pressures used.[85][110] In the case of spacesuitsHP Pavilion dv6-1218ss battery, the O2 partial pressure in the breathing gas is, in general, about 30 kPa (1.4 times normal), and the resulting O2 partial pressure in the astronaut's arterial blood is only marginally more than normal sea-level O2 partial pressure (for more information on this, see space suit and arterial blood gas) HP Pavilion dv6-1218ca battery.Oxygen toxicity to the lungs and central nervous system can also occur in deep scuba diving and surface supplied diving.[26][87] Prolonged breathing of an air mixture with an O2 partial pressure more than 60 kPa can eventually lead to permanent pulmonary fibrosis.[111] Exposure to a O2 partial pressures greater than 160 kPa (about 1.6 atm) may lead to convulsions (normally fatal for divers) HP Pavilion dv6-1217tx battery. Acute oxygen toxicity (causing seizures, its most feared effect for divers) can occur by breathing an air mixture with 21% O2 at 66 m or more of depth; the same thing can occur by breathing 100% O2 at only 6 m.Combustion and other hazardsThe interior of the Apollo 1 Command Module. Pure O2 at higher than normal pressure and a spark led to a fire and the loss of the Apollo 1 crewHP Pavilion dv6-1217ss battery.Highly concentrated sources of oxygen promote rapid combustion. Fire and explosion hazards exist when concentrated oxidants and fuels are brought into close proximity; however, an ignition event, such as heat or a spark, is needed to trigger combustion.[115] Oxygen itself is not the fuel, but the oxidant. Combustion hazards also apply to compounds of oxygen with a high oxidative potentialHP Pavilion dv6-1217er battery, such as peroxides, chlorates, nitrates, perchlorates, and dichromates because they can donate oxygen to a fire.Concentrated O2 will allow combustion to proceed rapidly and energetically.[115] Steel pipes and storage vessels used to store and transmit both gaseous and liquid oxygen will act as a fuel; and therefore the design and manufacture of O2 systems requires special training to ensure that ignition sources are minimizedHP Pavilion dv6-1217ax battery.[115] The fire that killed the Apollo 1 crew in a launch pad test spread so rapidly because the capsule was pressurized with pure O2 but at slightly more than atmospheric pressure, instead of the 1⁄3 normal pressure that would be used in a mission. HP Pavilion dv6-1216tx batteryLiquid oxygen spills, if allowed to soak into organic matter, such as wood, petrochemicals, and asphalt can cause these materials to detonate unpredictably on subsequent mechanical impact.[115] As with other cryogenic liquids, on contact with the human body it can cause frostbites to the skin and the eyesHP Pavilion dv6-1216ss battery.
Kenya, officially the Republic of Kenya, is a country in East Africa that lies on the equator. With the Indian Ocean to its south-east, it is bordered by Tanzania to the south, Uganda to the west, South Sudan to the north-west, Ethiopia to the north and Somalia to the north-eastHP Pavilion dv6-1103au battery.Kenya has a land area of 580,000 km2 and a population of nearly 41 million,[6] representing 42 different peoples and cultures.[7] The country is named after Mount Kenya, a significant landmark and second among Africa's highest mountain peaksHP Pavilion dv6-1102tx battery.Following a referendum and adoption of a new constitution in August 2010, Kenya is now divided into 47 counties that are semi-autonomous units of governance. These units are expected to be fully implemented by August 2012 – in time for the first general election under the new constitution. The counties will be governed by elected governors and will operate independent of the central government in NairobiHP Pavilion dv6-1102tu battery.The country's geography is as diverse as its multi-ethnic population. It has a warm and humid climate along its coastline on the Indian Ocean which changes to wildlife-rich savannah grasslands moving inland towards the capital Nairobi. Nairobi has a cool climate that gets colder approaching Mount KenyaHP Pavilion dv6-1102ax battery, which has three permanently snow-capped peaks. The warm and humid tropical climate reappears further inland towards lake Victoria, before giving way to temperate forested and hilly areas in the western region. The North Eastern regions along the border with Somalia and Ethiopia are arid and semi-arid areas with near-desert landscapesHP Pavilion dv6-1102au battery. The country also has significant geothermal activity that puts a lot of electricity in the national grid.Kenya's capital city, Nairobi, is situated next to a national park. The country is famous for its safaris and diverse world-famous wildlife reserves such as Tsavo National Park, the Maasai Mara, Nakuru National Park, and Aberdares National Park that attract tourists from all over the worldHP Pavilion dv6-1101tx battery.Lake Victoria, the world's second largest fresh-water lake (after Lake Superior in the US and Canada) and the world's largest tropical lake, is situated to the southwest and is shared with Uganda and Tanzania.As part of East Africa, Kenya has seen human habitation since the Lower Paleolithic period. The Bantu expansion reached the area by the first millennium AD, and the borders of the modern state comprise the crossroads of the Niger–CongoHP Pavilion dv6-1101tu battery, Nilo-Saharan, and Afro-Asiatic linguistic areas of Africa, making Kenya a truly multi-cultural state. European and Arab presence in Mombasa dates to the Early Modern period, but European exploration of the interior began only in the 19th century. The British Empire established the East Africa Protectorate in 1895, known from 1920 as the Kenya ColonyHP Pavilion dv6-1101so battery. The independent Republic of Kenya was founded in December 1963.The capital, Nairobi, is a regional commercial hub. The economy of Kenya is the largest by GDP in East and Central Africa.[8][9] Agriculture is a major employer and the country traditionally exports tea and coffee, and more recently fresh flowers to Europe. The service industry is a major economic driver, mostly the telecommunications sector, and contributes 62 percent of GDPHP Pavilion dv6-1101ax battery.Kenya is a member of the East African Community and produces world-class athletes such as world champions Paul Tergat, David Rudisha, and Vivian Cheruiyot.EtymologyFurther information: Names on Mount KenyaThe word Kenya', /ˈkɛnjə/, originates from the Kikuyu, Embu and Kamba names for Mount Kenya, "Kirinyaga", "Kirinyaa" and "Kiinyaa".[citation needed] Prehistoric volcanic eruptions of Mount Kenya (now extinct) HP Pavilion dv6-1101au battery may have resulted in its association with divinity and creation among the indigenous Kikuyu-related ethnic groups who are the native inhabitants of the agricultural land surrounding Mount. Kenya.[original research?]The Wakamba first pointed out the second mountain to Dr. Krapf called "Kĩ-Nyaa" or "Kĩĩma- Kĩĩyaa" which is similar to Kĩrĩma Kĩrĩnyaga in Kikuyu... HP Pavilion dv6-1100sv battery probably because the pattern of black rock and white snow on its peaks reminded them of the feathers of the cock ostrich.[10]The word "Nyaga" is a Kikuyu – Embu word to mean spot. It is a diminutive for "Manyaganyaga", Spots. The spots of the black rock and the white snow could be the origin of the words "Kĩrĩ-nyaga" which in this case means 'spotted'. Therefore, Mwene- Nyaga (Agikuyu God) means "The owner/guardian of the spotted Mountain"HP Pavilion dv6-1100ss battery.In the 19th century, the German explorer Ludwig Krapf recorded the name as both Kenia and Kegnia believed by some to be a corruption of the Kamba version.[11][12][13] Others say that this was—on the contrary—a very precise notation of a correct African pronunciation /ˈkɛnjə/.[14] A map drawn by Joseph Thompsons, 1882 a Scottish geologist and Naturalist indicated Mt. Kenya as Mt. Kenia, 18620HP Pavilion dv6-1100so battery.[10]Geography and climateMain articles: Geography of Kenya and Climate of KenyaSee also: Environmental issues in KenyaMount Kenya is the highest peak in Kenya at 5,199 m (17,057 ft).[15] Kenya is named after the mountain.[16]At 580,367 km2 (224,081 sq mi),[2] Kenya is the world's forty-seventh largest country (after Madagascar). It lies between latitudes 5°N and 5°S, and longitudes 34° and 42°E. From the coast on the Indian Ocean, the low plains rise to central highlandsHP Pavilion dv6-1100es battery. The highlands are bisected by the Great Rift Valley; a fertile plateau lies in the east. The Kenyan Highlands comprise one of the most successful agricultural production regions in Africa. The highlands are the site of the highest point in Kenya (and the second highest in Africa): Mount Kenya, which reaches 5,199 m (17,057 ft) and is the site of glaciers. Mount Kilimanjaro (5,895 m/19,341 ft) can be seen from Kenya to the South of the Tanzanian borderHP Pavilion dv6-1100eo battery.[15]Kenya's climate varies from tropical along the coast to temperate inland to arid in the north and northeast parts of the country. Kenya receives a great deal of sunshine all the year round, and summer clothes are worn throughout the year. It is usually cool at night and early in the morning inland at higher elevationsHP Pavilion dv6-1099ef battery. The "long rains" season occurs from March/April to May/June. The "short rains" season occurs from October to November/December. The rainfall is sometimes heavy and often falls in the afternoons and evenings. The temperature remains high throughout these months of tropical rain. The hottest period is February and March, leading into the season of the long rains, and the coldest is in July and AugustHP Pavilion dv6-1090es battery.Kenya has considerable land area devoted to wildlife habitats, including the Masai Mara, where Blue Wildebeest and other bovids participate in a large scale annual migration. Up to 250,000[citation needed] blue wildebeest perish each year in the long and arduous movement to find forage in the dry season. HP Pavilion dv6-1090eo battery [citation needed] The "Big Five" animals of Africa can be found in Kenya and in the Masai Mara in particular: the lion, leopard, buffalo, rhinoceros and elephant. A significant population of other wild animals, reptiles and birds can be found in the national parks and game reserves in the country. The annual animal migration – especially migration of the wildebeest –HP Pavilion dv6-1080es battery occurs between June and September with millions of animals taking part.Kenya is the setting for one of the Natural Wonders of the World – the great wildebeest migration. 11.5 million of these ungulates migrate a distance of 1,800 miles from the Serengeti in neighbouring Tanzania to the Masai Mara in Kenya, in a constant clockwise fashion, searching for food and water suppliesHP Pavilion dv6-1080eq battery.HistoryMain article: History of KenyaPrehistoryThe African theropod Spinosaurus was the largest known carnivorous dinosaur.Giant crocodile fossils have been discovered in Kenya, dating from the Mesozoic Era, over 200 million years ago. The fossils were found in an excavation conducted by a team from the University of Utah and the National Museums of Kenya in July–August 2004 at Lokitaung Gorge, near Lake TurkanaHP Pavilion dv6-1080el battery.[17]Fossils found in East Africa suggest that primates roamed the area more than 20 million years ago. Recent finds near Kenya's Lake Turkana indicate that hominids such as Homo habilis (1.8 and 2.5 million years ago) and Homo erectus (1.8 million to 350 000 years ago) are possible direct ancestors of modern Homo sapiens and lived in Kenya during the Pleistocene epochHP Pavilion dv6-1070eo battery. In 1984 one particular discovery made at Lake Turkana by famous palaeoanthropologist Richard Leakey and Kamoya Kimeu was the skeleton of a Turkana boy belonging to Homo erectus from 1.6 million years ago. Previous research on early hominids is particularly identified with Mary Leakey and Louis LeakeyHP Pavilion dv6-1068el battery, who were responsible for the preliminary archaeological research at Olorgesailie and Hyrax Hill. Later work at the former was undertaken by Glynn Isaac.[citation needed]Kenya has been inhabited by people for as long as human history has existed.Pre-colonial historyThe first inhabitants of present-day Kenya were hunter-gatherer groups, akin to the modern Khoisan speakersHP Pavilion dv6-1066el battery.[18] These people were later replaced by agropastoralist Cushitic speakers from the Horn of Africa.[19] During the early Holocene the regional climate shifted from dry to wetter climatic conditions, this provided an opportunity for the development of cultural traditions, such as agriculture and herding, in a more favorable environmentHP Pavilion dv6-1062el battery.[18]Around 500 BC Nilotic speaking pastoralists (ancestral to Kenya's Nilotic speakers) started migrating from present-day Southern Sudan into Kenya.[20][21][22] Nilotic groups in Kenya include the Samburu, Luo, Turkana, Maasai.[23]By the first millennium AD, Bantu speaking farmers moved into the region.[24] The Bantus originated in West Africa along the Benue River in what is now eastern Nigeria and western CameroonHP Pavilion dv6-1060ev battery.[25] The Bantu migration brought new developments in agriculture and iron working to the region.[25] Bantu groups in Kenya include the Kikuyu, Luhya, Kamba, Kisii, Meru, Aembu, Ambeere and Mijikenda among others.Arab traders began frequenting the Kenya coast around the 1st century AD. Kenya's proximity to the Arabian Peninsula invited colonization, and Arab and Persian settlements sprouted along the coast by the 8th centuryHP Pavilion dv6-1060es battery.The Kenyan coast had served host to communities of ironworkers and communities of subsistence farmers, hunters and fishers who supported the economy with agriculture, fishing, metal production and trade with foreign countries.[26]The Great Mosque of Kilwa Kisiwani, one of the many mosques built by the Persian founders of the Kilwa SultanateHP Pavilion dv6-1060eo battery.[27]The Kilwa Sultanate was a medieval sultanate, centered at Kilwa in modern-day Tanzania. At its height, its authority stretched over the entire length of the Swahili Coast, including Kenya. It was founded in the 10th century by Ali ibn al-Hassan Shirazi,[28] a Persian Prince of Shiraz.[29] The Persian rulers would go on to build elaborate coral mosques and introduced copper coinageHP Pavilion dv6-1060el battery.[27]During this period, Arabs from southern Arabia settled on the coast. They established many new autonomous city-states, including Mombasa, Malindi and Zanzibar. The Arab migrants also introduced Islam and the Omani dialect of Arabic to the area. This blending of cultures left a notable Arabian influence on the local Bantu Swahili culture and language of the coastHP Pavilion dv6-1058el battery.[30] The Arabs built Mombasa into a major port city and established trade links with other nearby city-states, as well as commercial centers in Persia, Arabia, and even India.[31] By the 15th-century, Portuguese voyager Duarte Barbosa claimed that "Mombasa is a place of great traffic and has a good harbour in which there are always moored small craft of many kinds and also great shipsHP Pavilion dv6-1056el battery, both of which are bound from Sofala and others which come from Cambay and Melinde and others which sail to the island of Zanzibar."[32]In the centuries preceding colonization, the Swahili coast of Kenya was part of the east African region which traded with the Arab world and India especially for ivory and slaves (the Ameru tribe is said to have originated from slaves escaping from Arab lands sometime around the year 1700HP Pavilion dv6-1055ee battery). Initially these traders came mainly from Arab states, but later many came from Zanzibar (such as Tippu Tip).[33] Close to 90% of the population on the Kenya coast was enslaved.[34]Swahili, a Bantu language with Arabic, Persian, and other Middle Eastern and South Asian loanwords, later developed as a lingua franca for trade between the different peoplesHP Pavilion dv6-1053cl battery.[26]Throughout the centuries the Kenyan Coast has played host to many merchants and explorers. Among the cities that line the Kenyan coast is the City of Malindi. It has remained an important Swahili settlement since the 14th century and once rivaled Mombasa for dominance in this part of East AfricaHP Pavilion dv6-1050us battery. Malindi has traditionally been a friendly port city for foreign powers. In 1414, the Arab Sultan of Malindi initiated diplomatic relations with Ming Dynasty China during the voyages of the explorer Zheng He.[35] Malindi authorities welcomed Portuguese explorer, Vasco da Gama, in 1498HP Pavilion dv6-1050et battery.Colonial historyMain article: History of Kenya#Colonial historyBritain's possessions in British East Africa during the colonial period.The colonial history of Kenya dates from the establishment of a German protectorate over the Sultan of Zanzibar's coastal possessions in 1885, followed by the arrival of the Imperial British East Africa Company in 1888. Incipient imperial rivalry was forestalled when Germany handed its coastal holdings to Britain in 1890HP Pavilion dv6-1050ep battery. This was followed by the building of the Kenya–Uganda railway passing through the country. This was resisted by some tribes — notably the Nandi led by Orkoiyot Koitalel Arap Samoei for ten years from 1895 to 1905 — still the British eventually built the railway. The Nandi were the first tribe to be put in a native reserve to stop them from disrupting the building of the railwayHP Pavilion dv6-1050eo battery. During the railway construction era, there was a significant inflow of Indian peoples, who provided the bulk of the skilled manpower required for construction.[36]While building the railroad through Tsavo, a number of the Indian railway workers and local African labourers were attacked by two lions known as the Tsavo maneatersHP Pavilion dv6-1050en battery. They and most of their descendants later remained in Kenya and formed the core of several distinct Indian communities such as the Ismaili Muslim and Sikh communities.[37][38]Statue of Dedan Kimathi, a Kenyan rebel leader with the Mau Mau who fought against British colonization in the 1950s.At the outbreak of World War I in August 1914, the governors of British East Africa (as the Protectorate was generally known)HP Pavilion dv6-1050ei battery and German East Africa agreed a truce in an attempt to keep the young colonies out of direct hostilities. Lt Col Paul von Lettow-Vorbeck took command of the German military forces, determined to tie down as many British resources as possible. Completely cut off from Germany, von Lettow conducted an effective guerilla warfare campaignHP Pavilion dv6-1050ef battery, living off the land, capturing British supplies, and remaining undefeated. He eventually surrendered in Zambia eleven days after the Armistice was signed in 1918. To chase von Lettow the British deployed the British Indian Army troops from India and then needed large numbers of porters to overcome the formidable logistics of transporting supplies far into the interior on footHP Pavilion dv6-1046el battery. The Carrier Corps was formed and ultimately mobilised over 400,000 Africans, contributing to their long-term politicisation.[36]During the early part of the 20th century, the interior central highlands were settled by British and other European farmers, who became wealthy farming coffee and tea.[39] (One depiction of this period of change from one colonist's perspective is found in the memoir "Out of Africa" by Danish author Baroness Karen von Blixen-FineckeHP Pavilion dv6-1045ez battery, published in 1937.) By the 1930s, approximately 30,000 white settlers lived in the area and gained a political voice because of their contribution to the market economy. The area was already home to over a million members of the Kikuyu people, most of whom had no land claims in European terms, and lived as itinerant farmers. To protect their interestsHP Pavilion dv6-1045eo battery, the settlers banned the growing of coffee, introduced a hut tax, and the landless were granted less and less land in exchange for their labour. A massive exodus to the cities ensued as their ability to provide a living from the land dwindled.[36] By the 1950s, the white population numbered 80,000HP Pavilion dv6-1045ei battery.[40]Kenya–Uganda railway near Mombasa, about 1899From October 1952 to December 1959, Kenya was under a state of emergency arising from the Mau Mau rebellion against British rule. The governor requested and obtained British and African troops, including the King's African Rifles. The British began counter-insurgency operations; in May 1953 General Sir George Erskine took charge as commander-in-chief of the colony's armed forcesHP Pavilion dv6-1045ee battery, with the personal backing of Winston Churchill.[41]The capture of Warũhiũ Itote (aka General China) on 15 January 1954, and the subsequent interrogation led to a better understanding of the Mau Mau command structure. Operation Anvil opened on 24 April 1954, after weeks of planning by the army with the approval of the War CouncilHP Pavilion dv6-1044el battery. The operation effectively placed Nairobi under military siege, and the occupants were screened and the Mau Mau supporters moved to detention camps. The Home Guard formed the core of the government's strategy as it was composed of loyalist Africans, not foreign forces like the British Army and King's African RiflesHP Pavilion dv6-1042el battery. By the end of the emergency, the Home Guard had killed 4686 Mau Mau, amounting to 42% of the total insurgents. The capture of Dedan Kimathi on 21 October 1956, in Nyeri signified the ultimate defeat of the Mau Mau and essentially ended the military offensive.[41] During this period, substantial governmental changes to land tenure occurredHP Pavilion dv6-1040ez battery, the most important of which was the Swynnerton Plan, which was used to both reward loyalists and punish Mau Mau.Post-colonial historyThe first direct elections for Africans to the Legislative Council took place in 1957. Despite British hopes of handing power to "moderate" African rivals, it was the Kenya African National Union (KANU) of Jomo Kenyatta that formed a government shortly before Kenya became independent on 12 December 1963HP Pavilion dv6-1040ev battery, on the same day forming the first Constitution of Kenya.[42] During the same year, the Kenyan army fought the Shifta War against ethnic Somalis who wanted Kenya's Northern Frontier District joined with the Republic of Somalia. The Shifta War officially ended with the signature of the Arusha Memorandum in October, 1967, but relative insecurity prevailed through 1969HP Pavilion dv6-1040el battery.[43][44] To discourage further invasions, Kenya signed a defence pact with Ethiopia in 1969, which is still in effect.[45]The former Kenyan President and founder of Kenya, Jomo Kenyatta.On 12 December 1964 the Republic of Kenya was proclaimed, and Jomo Kenyatta became Kenya's first president.[46] At Kenyatta's death in 1978, Daniel arap Moi became President. Daniel arap Moi retained the PresidencyHP Pavilion dv6-1040ek battery, being unopposed in elections held in 1979, 1983 (snap elections) and 1988, all of which were held under the single party constitution. The 1983 elections were held a year early, and were a direct result of an abortive military coup attempt on 2 August 1982.The abortive coup was masterminded by a low ranked Air Force serviceman, Senior Private Hezekiah Ochuka and was staged mainly by enlisted men in the Air ForceHP Pavilion dv6-1040ei battery. The attempt was quickly suppressed by Loyalist forces led by the Army, the General Service Unit (GSU) — a paramilitary wing of the police — and later the regular police, but not without civilian casualties. This event led to the disbanding of the entire Air Force and a large number of its former members were either dismissed or court-martialledHP Pavilion dv6-1040ed battery.The election held in 1988 saw the advent of the mlolongo (queuing) system, where voters were supposed to line up behind their favoured candidates instead of a secret ballot.[47] This was seen as the climax of a very undemocratic regime and it led to widespread agitation for constitutional reform. Several contentious clausesHP Pavilion dv6-1040eb battery, including one that allowed for only one political party were changed in the following years.[48] In democratic, multiparty elections in 1992 and 1997, Daniel arap Moi won re-election. In 2002, Moi was constitutionally barred from running, and Mwai Kǐbakǐ, running for the opposition coalition "National Rainbow Coalition" HP Pavilion dv6-1038ca battery-- NARC, was elected President. Anderson (2003) reports the elections were judged free and fair by local and international observers, and seemed to mark a turning point in Kenya's democratic evolution.[49]PoliticsMain article: Politics of KenyaCurrent president Mwai KibakiKenya is a presidential representative democratic republic, whereby the President is both the head of state and head of government, and of a multi-party systemHP Pavilion dv6-1030us battery. Executive power is exercised by the government. Legislative power is vested in both the government and the National Assembly. The Judiciary is independent of the executive and the legislature. There was growing concern especially during former president Daniel arap Moi's tenure that the executive was increasingly meddling with the affairs of the judiciary. HP Pavilion dv6-1030eq batteryKenya has maintained remarkable stability despite changes in its political system and crises in neighbouring countries. A cross-party parliamentary reform initiative in the autumn of 1997 revised some oppressive laws inherited from the colonial era that had been used to limit freedom of speech and assembly. This improved public freedoms and contributed to generally credible national elections in December 1997HP Pavilion dv6-1030eo battery.[citation needed]In December 2002, Kenyans held democratic and open elections, most of which were judged free and fair by international observers. The 2002 elections marked an important turning point in Kenya's democratic evolution in that power was transferred peacefully from the Kenya African Union (KANU) HP Pavilion dv6-1030em battery, which had ruled the country since independence to the National Rainbow Coalition (Narc), a coalition of political parties.Under the presidency of Mwai Kibaki, the new ruling coalition promised to focus its efforts on generating economic growth, combating corruption, improving education, and rewriting its constitution. A few of these promises have been met. There is free primary educationHP Pavilion dv6-1030ef battery. In 2007 the government issued a statement declaring that from 2008, secondary education would be heavily subsidised, with the government footing all tuition fees.[citation needed]2007 electionsMain article: Kenyan presidential election, 2007Post-election violence in NairobiThe latest general elections were held on 27 December 2007. In them, President Kibaki under the Party of National Unity ran for re-election against the main opposition party, the Orange Democratic Movement (ODM) HP Pavilion dv6-1030ed battery. The elections were seen to have been flawed with international observers saying that they were below international standards. After a split which would take a crucial 8% of the votes away from the ODM to the newly formed Orange Democratic Movement-Kenya (ODM-K)'s candidate, Kalonzo Musyoka, the race tightened between ODM candidate Raila Odinga and KibakiHP Pavilion dv6-1030ec battery. As the count came in to the Electoral Commission of Kenya (ECK) headquarters, Odinga was shown to have a slight, and then substantial lead as the results from his strongholds came in early. As the ECK continued to count the votes, Kibaki closed the gap and then overtook his opponent by a substantial margin after votes from his stronghold arrived laterHP Pavilion dv6-1030ca battery. This led to protests and open discrediting of the ECK for complicity and to Odinga declaring himself the "people's president" and calling for a recount.[50]The protests escalated into ethnic violence and destruction of property, almost 1,000 people were killed and nearly 600,000 displaced. The dispute caused underlying tensions over land and its distribution to re-erupt, as it had in the 1992 and 1997 electionsHP Pavilion dv6-1027ef battery.[53] Hundreds of thousands were forced off their land to relatives elsewhere in the country and some claim weapons are being bought in the region, perhaps in anticipation of the 2012 elections.[53]A group of eminent persons of Africa, led by former United Nations secretary-general Kofi Annan, brokered a peaceful solution to the political stalemateHP Pavilion dv6-1025ez battery.2008Current prime minister Raila OdingaOn 28 February 2008, Kibaki and Odinga signed an agreement on the formation of a coalition government in which Odinga would become Kenya's second prime Minister. Under the deal, the president would appoint cabinet ministers from both PNU and ODM camps depending on each party's strength in ParliamentHP Pavilion dv6-1025ei battery. The agreement stipulated that the cabinet would include a vice-president and two deputy Prime Ministers. After being debated and passed by Parliament, the coalition would hold until the end of the current Parliament or if either of the parties withdraws from the deal before then.[citation needed] HP Pavilion dv6-1025ef batteryThe new office of the PM will have power and authority to co-ordinate and supervise the functions of the Government and will be occupied by an elected MP who will be the leader of the party or coalition with majority members in Parliament. The world watched Annan and his UN-backed panel and African Union chairman Jakaya Kikwete as they brought together the erstwhile rivals to the signing ceremonyHP Pavilion dv6-1023em battery, beamed live on national TV from the steps of Nairobi's Harambee House. On 29 February 2008, representatives of PNU and ODM began working on the finer details of the power-sharing agreement.[54] Kenyan lawmakers unanimously approved a power-sharing deal 18 March 2008, aimed at salvaging a country usually seen as one of the most stable and prosperous in AfricaHP Pavilion dv6-1023ef battery. The deal brought Kibaki's PNU and Odinga's ODM together and heralded the formation of the grand coalition, in which the two political parties would share power equally.[55]Grand coalitionOn 13 April 2008, President Kibaki named a grand coalition cabinet of 41 Ministers- including the prime minister and his two deputiesHP Pavilion dv6-1022el battery. The cabinet, which included 50 Assistant Ministers, was sworn in at the State House in Nairobi on Thursday, 17 April 2008 in the presence of Dr. Kofi Annan and other invited dignitaries.A constitutional change was considered that would eliminate the position of Prime Minister[56] and simultaneously reduce the powers of the PresidentHP Pavilion dv6-1020et battery. A referendum to vote on the proposed constitution was held on 4 August 2010, and the new constitution passed by a wide margin.[57] Among other things, the new constitution delegates more power to local governments and gives Kenyans a bill of rights.[58] It was promulgated on 27 August 2010 at a euphoric ceremony in Nairobi's Uhuru ParkHP Pavilion dv6-1020eg battery, accompanied by a 21-gun salute. The event was graced by a number of African leaders and praised by the international community. As of that day, the new constitution heralding the Second Republic came into force.Administrative regionsMain articles: Provinces of Kenya, Districts of Kenya, and Divisions of KenyaProvinces of KenyaKenya is divided into 47 semi-autonomous counties that will be headed by governors who will be elected in the first general election under the new constitution in August 2012HP Pavilion dv6-1020el battery (There is still controversy over whether the elections should be held in August or December 2012). Under the old constitution, Kenya comprised eight provinces each headed by a Provincial Commissioner (centrally appointed by the president). The provinces (mkoa singular mikoa plural in Swahili) were subdivided into districts (wilaya) HP Pavilion dv6-1020ek battery. There were 69 districts as of 1999 census. Districts are then subdivided into 497 divisions (taarafa). The divisions are then subdivided into 2,427 locations (mtaa) and then 6,612 sublocations (mtaa mdogo).[59] The City of Nairobi enjoys the status of a full administrative province. The government supervises administration of districts and provinces. The provinces areHP Pavilion dv6-1020ei battery:Under the current Kenya constitution, local government authorities are not recognized. However, under the old constitution, local governance in Kenya was practised through local authorities. Many urban centres host city, municipal or town councils. Local authorities in rural areas are known as county councils. Local councillors are elected by civic elections, which are held alongside general electionsHP Pavilion dv6-1020ed battery.Constituencies are an electoral subdivision. An Interim Boundaries commission was formed in year 2010 to review the constituencies and in its report, it recommended creation of additional 80 constituencies. Currently, there are 210 Constituencies in KenyaHP Pavilion dv6-1020ec battery.[60]Economy20 shilling note from 1994, depicting then-President Daniel arap MoiMain article: Economy of KenyaDespite western donors' early disillusionment with the government, the economy has seen much expansion, seen by strong performance in tourism, higher education and telecommunications, and acceptable post-drought results in agriculture, especially the vital tea sector.[61] Kenya's economy grew by more than 7% in 2007HP Pavilion dv6-1018el battery, and its foreign debt was greatly reduced.[61] But this changed immediately after the disputed presidential election of December 2007, following the chaos which engulfed the country.East and Central Africa's biggest economy has posted tremendous growth in the service sector, boosted by rapid expansion in telecommunication and financial activity over the last decade, and now contributes 62 percent of GDPHP Pavilion dv6-1001et battery. Unfortunately, a massive 22 percent of GDP still comes from the unreliable agricultural sector which employs 75 percent of the labor force (a consistent characteristic of under-developed economies that have not attained food security – an important catalyst of economic growth) and a significant portion of the population regularly starves and is heavily dependent on food aidHP Pavilion dv6-1001tx battery. Industry and manufacturing is the smallest sector that accounts for 16 percent of the GDP.Kenya has traditionally been a liberal market with minimal government involvement (price control) seen in the oil industry. However, recent legislation allows the government to determine and gazette price-controls on essential commodities like maize flour, kerosine and cooking oilHP Pavilion dv6-1001xx battery.Privatisation of state corporations like the defunct Kenya Post and Telecommunications Company, which resulted in East Africa's most profitable company – Safaricom, has led to their revival due to massive private investment.As of May 2010, economic prospects are positive with 4–5% GDP growth expected, largely because of expansions in tourism, telecommunicationsHP Pavilion dv6-1002tx battery, transport, construction and a recovery in agriculture. The World Bank predicts growth of 4% in 2010 and a potential of 4.9% growth in 2011.[62]In March 1996, the Presidents of Kenya, Tanzania, and Uganda re-established the East African Community (EAC). The EAC's objectives include harmonizing tariffs and customs regimes, free movement of people, and improving regional infrastructuresHP Pavilion dv6-1003tx battery. In March 2004, the three East African countries signed a Customs Union Agreement.The more efficient and lucrative technology-knowledge-and-skill-based service; industry and manufacturing sectors only employ 25 percent of the labor force but contributes the remaining 75 percent of the GDPHP Pavilion dv6-1004tx battery.[61]Kenya ranks poorly on Transparency International's corruption perception index.[63]Kenya is East and Central Africa's hub for Financial services. The Nairobi Securities Exchange (NSE) is ranked 4th in Africa in terms of Market capitalization.[citation needed] The Kenya banking system is supervised by the Central Bank of Kenya (CBK) HP Pavilion dv6-1005ea battery. As of late July 2004, the system consisted of 43 commercial banks (down from 48 in 2001), several non-bank financial institutions, including mortgage companies, four savings and loan associations, and several score foreign-exchange bureaus.[61]TourismMain article: Tourism in KenyaTourists on a safari in KenyaKenya's services sector, which contributes about 63 percent of GDP, is dominated by tourism. The tourism sector has exhibited steady growth in most years since independence and by the late 1980s had become the country's principal source of foreign exchangeHP Pavilion dv6-1005ez battery. Tourists, the largest number from Germany and the United Kingdom, are attracted mainly to the coastal beaches and the game reserves, notably, the expansive Tsavo National Park (20,808 square kilometers) in the southeast. Tourism has seen a substantial revival over the past several years and is the major contributor to the pick-up in the country's economic growthHP Pavilion dv6-1005tx battery. Tourism is now Kenya's largest foreign exchange earning sector, followed by flowers, tea, and coffee. In 2006 tourism generated US$803 million, up from US$699 million the previous year.AgricultureMain article: Agriculture in KenyaCultivation on the slopes of Mount KenyaAgriculture is the second largest contributor to Kenya's gross domestic product (GDP), after the service sector. In 2005 agriculture, including forestry and fishing, accounted for about 24 percent of GDPHP Pavilion dv6-1006tx battery, as well as for 18 percent of wage employment and 50 percent of revenue from exports. The principal cash crops are tea, horticultural produce, and coffee; horticultural produce and tea are the main growth sectors and the two most valuable of all of Kenya's exports. The production of major food staples such as corn is subject to sharp weather-related fluctuationsHP Pavilion dv6-1007tx battery. Production downturns periodically necessitate food aid—for example, in 2004 aid for 1.8 million people because of one of Kenya's intermittent droughts.[citation needed] Tea, coffee, sisal, pyrethrum, corn, and wheat are grown in the fertile highlands, one of the most successful agricultural production regions in AfricaHP Pavilion dv6-1008tx battery. Livestock predominates in the semi-arid savanna to the north and east. Coconuts, pineapples, cashew nuts, cotton, sugarcane, sisal, and corn are grown in the lower-lying areas.Unfortunately, the country has not attained the level of investment and efficiency in agriculture that can guarantee food security and coupled with resulting poverty (53 percent of the population lives below the poverty line) HP Pavilion dv6-1009el battery, a significant portion of the population regularly starves and is heavily dependent on food aid. Poor roads, an inadequate railway network, under-utilised water transport and expensive air transport have isolated mostly arid and semi-arid areas and farmers in other regions often leave food to rot in the fields because they cannot access marketsHP Pavilion dv6-1009tx battery. This was last seen in August and September 2011 prompting the Kenyans for Kenya initiative by the Red Cross.[64]Industry and manufacturingAlthough Kenya is the most industrially developed country in East Africa, manufacturing still accounts for only 14 percent of gross domestic product (GDP). Industrial activity, concentrated around the three largest urban centers, Nairobi, Mombasa, and KisumuHP Pavilion dv6-1010ea battery, is dominated by food-processing industries such as grain milling, beer production, and sugarcane crushing, and the fabrication of consumer goods, e.g., vehicles from kits. There is a vibrant and fast growing cement production industry.[citation needed] Kenya has an oil refinery that processes imported crude petroleum into petroleum productsHP Pavilion dv6-1010ed battery, mainly for the domestic market. In addition, a substantial and expanding informal sector commonly referred to as Jua Kali engages in small-scale manufacturing of household goods, motor-vehicle parts, and farm implements.[citation needed]Kenya's inclusion among the beneficiaries of the U.S. Government's African Growth and Opportunity Act (AGOA) has given a boost to manufacturing in recent years. Since AGOA took effect in 2000HP Pavilion dv6-1010et battery, Kenya's clothing sales to the United States increased from US$44 million to US$270 million (2006).[citation needed] Other initiatives to strengthen manufacturing have been the new government's favorable tax measures, including the removal of duty on capital equipment and other raw materials. HP Pavilion dv6-1010tx batteryEnergyLogo of KenGen, the largest electricity producer in Kenya.The largest share of Kenya's electricity supply comes from hydroelectric stations at dams along the upper Tana River, as well as the Turkwel Gorge Dam in the west. A petroleum-fired plant on the coast, geothermal facilities at Olkaria (near Nairobi), and electricity imported from Uganda make up the rest of the supplyHP Pavilion dv6-1011tx battery. Kenya's installed capacity stood at 1,142 megawatts between 2001 and 2003. The state-owned Kenya Electricity Generating Company (KenGen), established in 1997 under the name of Kenya Power Company, handles the generation of electricity, while the Kenya Power and Lighting Company (KPLC), which is slated for privatization, handles transmission and distributionHP Pavilion dv6-1012tx battery. Shortfalls of electricity occur periodically, when drought reduces water flow. To become energy sufficient, Kenya aims to build a nuclear power plant by 2017.[65]Workers at Olkaria Geothermal Power PlantHydrocarbon reserves have yet to be discovered on Kenya's territory, despite several decades of intermittent exploration. Kenya currently imports all crude petroleum requirementsHP Pavilion dv6-1013ea battery. Kenya, east Africa's largest economy, has no strategic reserves and relies solely on oil marketers' 21-day oil reserves required under industry regulations. Petroleum accounts for 20 to 25 percent of the national import bill.[66]Although Kenya is yet to give a formal indication of where its exploration program, which now involves half a dozen companies, is headed, in recent weeks, well-placed sources in Uganda's oil industry have suggested that the country is on the verge on making an announcement that could cement East Africa's position as major oil region on the continentHP Pavilion dv6-1013tx battery. Optimism surrounding the Kenyan program is informed by recent oil discoveries in Uganda that, combined with the fact that the rocks that form the East African Rift System are about the same age, suggests a high potential for oil in Kenya. Gas discoveries in Tanzania and significant proven oil reserves along the border between Uganda and DR Congo have also encouraged interest in the once largely overlooked regionHP Pavilion dv6-1016ez battery. Reacting to the current speculation about prospects for an early oil find, senior geologists at Uganda's Energy Ministry who were at the forefront of the country's search for oil two decades ago, said they had no reason to doubt that there was oil in Kenya, with the area around Lake Turkana and the coastal belt being singled out as the most promising prospects. HP Pavilion dv6-6091nr batteryBefore its exit mid this year, China National Offshore Oil Corporation (CNOOC) had worked with Africa Oil and Lion Energy Corp to drill an exploratory well in block 9 in northern Kenya. It also had a license for block L2, an inland area in the Lamu basinHP Pavilion dv6-6090us battery.[67]Vision 2030In 2007, the Kenyan government unveiled Vision 2030, an economic blueprint it hopes will put the country in the same league as the Asian Economic Tigers by the year 2030.Oil explorationOn 26 March 2012, Kenyan President Mwai Kibaki announced that oil had been discovered in the Turkana District after exploratory drilling by Anglo-Irish firm Tullow Oil, and he further stated that HP Pavilion dv6-6090sf battery"It is... the beginning of a long journey to make our country an oil producer, which typically takes in excess of three years. We shall be giving the nation more information as the oil exploration process continues[68]Early in 2006 Chinese President Hu Jintao signed an oil exploration contract with Kenya, the latest in a series of deals designed to keep Africa's natural resources flowing to China's rapidly expanding economyHP Pavilion dv6-6087eg battery.The deal allowed for China's state-controlled offshore oil and gas company, CNOOC, to prospect for oil in Kenya, which is just beginning to drill its first exploratory wells on the borders of Sudan and Somalia and in coastal waters. No oil has been discovered yet, and there has been no formal estimate of the possible reservesHP Pavilion dv6-6063sf battery.[69]DemographicsMain article: Demographics of KenyaKikuyu woman in traditional attire.Kenya has a young population, with 73% of residents aged below 30 years, due to rapid population growth;[70] from 2.9 million to 40 million over the last century.[71]Kenya's rising urban population has a diverse ethnic background whose people are variedly fluent in their mother tongues and the two official languages – English and Swahili. Peri-urban and rural populations are less multilingual with many in remote villages speaking only their mother tongueHP Pavilion dv6-6054sf battery.Ethnic groupsKikuyu 22%, Luhya 14%, Luo 13%, Kalenjin 12%, Kamba 11%, Kisii 6%, Meru 6%, other African 15%, non-African (Asian, European, and Arab) 1%.[2]In addition, Kenya's capital, Nairobi, is home to Kibera, one of the world's largest slums. The shanty town is believed to house between 170,000[72] and 1 million locals.[73] The UNHCR base in Dadaab in the north also currently houses around 500,000 peopleHP Pavilion dv6-6054ef battery.[74]ReligionMain article: Religion in KenyaHoly Ghost RC cathedral in Mombasa.The vast majority of Kenyans are Christian (83%), with 47.7% regarding themselves as Protestant and 23.5% as Roman Catholic.[75] Sizeable minorities of other faiths do exist (Muslim 11.2%, indigenous beliefs 1.7%).[75] Sixty percent of the Muslim population lives in Coast Province, comprising 50 percent of the total population thereHP Pavilion dv6-6051xx battery. Western areas of Coast Province are mostly Christian. The upper part of Eastern Province is home to 10 percent of the country's Muslims, where they constitute the majority religious group.[76] In addition, there is a large Hindu population in Kenya (around 50,000), who have played a key role in the local economy. There is also a small group of Baha'isHP Pavilion dv6-6051sf battery.[77]HealthMain article: Health in KenyaSee also: Healthcare in KenyaDespite major achievements in the health sector, Kenya still faces many challenges. Recent life expectancy estimates are approximately 55 years in 2009 – five years below 1990 levels.[78] Too many women and children still die at birth or within the first year of life. More die before their 5th birthdayHP Pavilion dv6-6042sf battery.Preventable diseases such as malaria, HIV/AIDS, pneumonia, diarrhea and malnutrition are the major child killers and responsible for much morbidity. Weak policies, inadequate health workers, weak management and poor leadership in most public health facilities are largely to blame. According to 2009 estimatesHP Pavilion dv6-6029tx battery, HIV prevalence is about 6.3% of the adult population.[79] However, the 2011 UNAIDS Report suggests that the HIV epidemic may be improving in Kenya, as HIV prevalence is declining among young people (ages 15–24) and pregnant women.[80]The total fertility rate in Kenya is estimated to be 4.49 children per woman in 2012.[81] Maternal mortality is high, partly because of female genital mutilationHP Pavilion dv6-6027tx battery.[61] This practice is however on the decline as the country becomes more modernised and the practice was also banned in the country in 2011.[82]EducationMain article: Education in KenyaSchool children in a classroom.Kenya's education system consists of early childhood education, primary, secondary and college.The country's literacy level stands at 85% of the whole population. Early childhood education takes at least three years, primary eight years, secondary four and university four or six years depending on the courseHP Pavilion dv6-6026tx battery. Preschool, which targets children from age three to five, is an integral component of the education system and is a key requirement for admission to Standard One (First Grade). At the end of primary education, pupils sit the Kenya Certificate of Primary Education (KCPE), which determines those who proceed to secondary school or vocational training. Primary school age is 6/7-13/14 yearsHP Pavilion dv6-6025tx battery. For those who proceed to secondary level, there is a national examination at the end of Form Four – the Kenya Certificate of Secondary Education (KCSE), which determines those proceeding to the universities, other professional training or employment. The Joint Admission Board (JAB) is responsible for selecting students joining the public universities. Other than the public schoolsHP Pavilion dv6-6024tx battery, there are many private schools in the country, mainly in urban areas. Similarly, there are a number of international schools catering for various overseas educational systems.Historical backgroundIndependent Kenya's first system of education was introduced by British colonists.[83] After Kenya's independence on 12 December 1963, an authority named the Ominde Commission was formed to introduce changes that would reflect the nation's sovereigntyHP Pavilion dv6-6023tx battery. The commission focused on identity and unity, which were critical issues at the time. Changes in the subject content of history and geography were made to reflect national cohesion. Between 1964 and 1985, the 7–4–2–3 system was adopted – seven years of primary, four years of lower secondary, two years of upper secondary, and three years of university. All schools had a common curriculumHP Pavilion dv6-6022eg battery.[83]In 1981, the Presidential Working Party on the Second University was commissioned to look at both the possibilities of setting up a second university in Kenya as well as the reforming of the entire education system.[83] The committee recommended that the 7–4–2–3 system be changed to an 8–4–4 system (eight years in primary, four years in secondary, and four years in university education) HP Pavilion dv6-6013tu battery. The table under Present-day education in Kenya below shows the structure of the 8–4–4 system. Although the 7–4–2–3 system theoretically ended with the introduction of the new 8–4–4 system in 1985, the last batch of students from the former system graduated from Kenyan Universities in 1992HP Pavilion dv6-6013cl battery.[83]Present-day education in KenyaAn MSc student at Kenyatta University in NairobiThe current 8–4–4 system was launched in January 1985.[84][85] It put more emphasis on vocational subjects on the assumption that the new structure would enable school dropouts at all levels either to be self-employed or to secure employment in the informal sectorHP Pavilion dv6-6012tu battery.In January 2003, the Government of Kenya announced the introduction of free primary education. As a result, primary school enrollment increased by about 70%. Secondary and tertiary education enrollment has not increased proportionally because payment is still required for attendanceHP Pavilion dv6-6011tu battery.In class eight of primary school the Kenya Certificate of Primary Examination (K.C.P.E.) is taken. The result of this examination is needed for placement at secondary school. In form four of secondary schools the Kenya Certificate of Secondary Examination (K.C.S.E.) is taken. Students sit examinations in eight subjects of their choosingHP Pavilion dv6-6008tx battery. However, English, KiSwahili (Languages) and Mathematics are compulsory subjects.Private schooling also exists in Kenya.In 2007 the government issued a statement declaring that from 2008, secondary education would be heavily subsidized, with the government footing all tuition feesHP Pavilion dv6-6008sa battery.CultureMain article: Culture of KenyaDressed up Maasai warriorsKenya is a diverse country. Notable peoples include the Swahili on the coast, pastoralist communities in the north, and several different communities in the central and western regions. The Maasai culture is well known because of tourism, despite being a minor percentage of the Kenyan population. They are renowned for their elaborate upper body adornment and jewelryHP Pavilion dv6-6008eg battery.Kenya has an extensive music, television and theatre scene.LiteratureMain article: Literature of KenyaNgũgĩ wa Thiong'o is one of the best known writers of Kenya. His book, Weep Not, Child is an illustration of life in Kenya during the British occupation. This is a story about the effects of the Mau Mau on the lives of black Kenyans. Its combination of themes—colonialism, education, and love—helped to make it one of the best-known novels in AfricaHP Pavilion dv6-6007tx battery.M.G. Vassanji's 2003 novel The In-Between World of Vikram Lall won the Giller Prize in 2003. It is the fictional memoir of a Kenyan of Indian heritage and his family as they adjust to the changing political climates in colonial and post-colonial Kenya.Since 2003, the literary journal Kwani? has been publishing Kenyan contemporary literatureHP Pavilion dv6-6007sg battery.MusicMain article: Music of KenyaPopular Kenyan musician Jua Cali.Kenya has a diverse assortment of popular music forms, in addition to multiple types of folk music based on the variety over 40 regional languages.[86]The guitar is the most dominant instrument in Kenyan popular music. Guitar rhythms are very complex and include both native beats and imported ones, especially the Congolese cavacha rhythmHP Pavilion dv6-6006ea battery; music usually involves the interplay of multiple parts and, more recently, showy guitar solos.Lyrics are most often in Swahili or English. There's also some emerging aspect of Lingala borrowed from Congo musicians. Lyrics are also written in the indigenous languages, though urban radio will generally not play music in one of the "tribal" languages. This however has been seen through the emergence of vernacular radio stations that broadcast in native languagesHP Pavilion dv6-6005sg battery.Benga music has been popular since the late 1960s, especially around Lake Victoria. The word benga is occasionally used to refer to any kind of pop music. bass, guitar and percussion are the usual instruments.Zanzibaran taarab music has also become popular, as has hip hop, reggae, soul, soukous, zouk, rock and roll, funk and EuropopHP Pavilion dv6-6005eg battery.SportsMain article: Sport in KenyaKenya is active in several sports, among them cricket, rallying, football (soccer), rugby union and boxing. But the country is known chiefly for its dominance in Middle-distance and long-distance athletics. Kenya has consistently produced Olympic and Commonwealth Games champions in various distance eventsHP Pavilion dv6-6005ea battery, especially in 800 m, 1,500 m, 3,000 m steeplechase, 5,000 m, 10,000 m and the marathon. Kenyan athletes (particularly Kalenjin) continue to dominate the world of distance running, although competition from Morocco and Ethiopia has reduced this supremacy. Kenya's best-known athletes included the four-time women's Boston Marathon winner and two-time world champion Catherine NderebaHP Pavilion dv6-6004sa battery, former Marathon world record-holder Paul Tergat, and John Ngugi.Top Kenyan middle-distance runner, David Rudisha.Kenya won several medals during the Beijing Olympics, five gold, five silver and four bronze, making it Africa's most successful nation in the 2008 Olympics. New athletes gained attention, such as Pamela Jelimo, the women's 800m gold medalist who went ahead to win the IAAF Golden League jackpot, and Samuel Wanjiru who won the men's marathonHP Pavilion dv6-6003eg battery. Retired Olympic and Commonwealth Games champion Kipchoge Keino helped usher in Kenya's ongoing distance dynasty in the 1970s and was followed by Commonwealth Champion Henry Rono's spectacular string of world record performances. Lately, there has been controversy in Kenyan athletics circles, with the defection of a number of Kenyan athletes to represent other countries, chiefly Bahrain and QatarHP Pavilion dv6-6002sg battery.[87] The Kenyan Ministry of Sports has tried to stop the defections, but they have continued anyway, with Bernard Lagat the latest, choosing to represent the United States.[87] Most of these defections occur because of economic or financial factors. Some elite Kenyan runners who cannot qualify for their country's strong national team find it easier to qualify by running for other countries. HP Pavilion dv6-6002eg battery Kenya has been a dominant force in women's volleyball within Africa, with both the clubs and the national team winning various continental championships in the past decade.[citation needed] The women's team has competed at the Olympics and World Championships but without any notable success. Cricket is another popular and the most successful team sportHP Pavilion dv6-6001sg battery. Kenya has competed in the Cricket World Cup since 1996. They upset some of the World's best teams and reached semi-finals of the 2003 tournament. They won the inaugural World Cricket League Division 1 hosted in Nairobi and participated in the World T20. Their current captain is Collins Obuya. They participated in the ICC Cricket World Cup 2011HP Pavilion dv6-6001eg battery. Kenya is represented by Lucas Onyango as a professional rugby league player who plays with Oldham Roughyeds. Besides the former European Super League team, he has played for Widnes Vikings and rugby union with Sale Sharks.[88] Rugby union is increasing in popularity. It is popular in Kenya especially with the annual Safari Sevens tournamentHP Pavilion dv6-6001ea battery. Kenya sevens team ranked 9th in IRB Sevens World Series for the 2006 season. Kenya was a regional power in soccer but its dominance has been eroded by wrangles within the Kenya Football Federation.[89] This has led to a suspension by FIFA which was lifted in March, 2007. In the motor rallying arena, Kenya is home to the world famous Safari RallyHP Pavilion dv6-6000eg battery, commonly acknowledged as one of the toughest rallies in the world,[90] and a part of the World Rally Championship for many years until its exclusion after the 2002 event owing to financial difficulties. Some of the best rally drivers in the world have taken part in and won the rally, such as Björn Waldegård, Hannu Mikkola, Tommi MäkinenHP Pavilion dv6-6000 battery , Shekhar Mehta, Carlos Sainz and Colin McRae. Though the rally still runs annually as part of the Africa rally championship, the organisers are hoping to be allowed to rejoin the World Rally championship in the next couple of years.
Iron is a chemical element with the symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is the most common element (by mass) forming the planet Earth as a whole(Sony VAIO VGN-AW11M/H battery), forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Iron's very common presence in rocky planets like Earth is due to its abundant production as a result of fusion in high-mass stars, where the production of nickel-56 (which decays to the most common isotope of iron) is the last nuclear fusion reaction that is exothermic(Sony VAIO VGN-AW11S/B battery). This causes radioactive nickel to become the last element to be produced before collapse of a supernova leads to the explosive events that scatter this precursor radionuclide of iron abundantly into space.Like other group 8 elements, iron exists in a wide range of oxidation states, −2 to +8, although +2 and +3 are the most common(Sony VAIO VGN-AW11Z/B battery). Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give iron oxides, also known as rust. Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron metal, and thus iron oxides flake off and expose fresh surfaces for corrosion(Sony VAIO VGN-AW170C battery).Iron metal has been used since ancient times, though lower-melting copper alloys were used first in history. Pure iron is soft (softer than aluminium), but is unobtainable by smelting. The material is significantly hardened and strengthened by impurities from the smelting process, such as carbon(Sony VAIO VGN-AW19/Q battery). A certain proportion of carbon (between 0.2% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to cast iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steel(Sony VAIO VGN-AW19 battery). Steels and low carbon iron alloys with other metals (alloy steels) are by far the most common metals in industrial use, due to their great range of desirable properties.Iron chemical compounds, which include ferrous and ferric compounds, have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. It forms binary compounds with the halogens and the chalcogens(Sony VAIO VGN-AW21M/H battery). Among its organometallic compounds, ferrocene was the first sandwich compound discovered.Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen transport proteins in vertebrates. Iron is also the metal used at the active site of many important redox enzymes dealing with cellular respiration and oxidation(Sony VAIO VGN-AW21S/B battery)Characteristics[edit]Mechanical propertiesThe mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test and the Vickers hardness test. The data on iron is so consistent that it is often used to calibrate measurements or to compare tests.[5][6] However, the mechanical properties of iron are significantly affected by the sample's purity(Sony VAIO VGN-AW21VY/Q battery): pure research-purpose single crystals of iron are actually softer than aluminium,[4] and the purest industrially produced iron (99.99%) has a hardness of 20–30 Brinell.[7] An increase in the carbon content of the iron will initially cause a significant corresponding increase in the iron's hardness and tensile strength(Sony VAIO VGN-AW21XY/Q battery). Maximum hardness of 65 Rc is achieved with a 0.6% carbon content, although this produces a metal with a low tensile strength.[8][edit]Phase diagram and allotropesMain article: Allotropes of ironIron represents an example of allotropy in a metal. There are at least four allotropic forms of iron, known as α, γ, δ, and ε; at very high pressures, some controversial experimental evidence exists for a phase β stable at very high pressures and temperatures(Sony VAIO VGN-AW21Z/B battery).[9]Low-pressure phase diagram of pure ironAs molten iron cools down it crystallizes at 1538 °C into its δ allotrope, which has a body-centered cubic (bcc) crystal structure. As it cools further its crystal structure changes to face-centered cubic (fcc) at 1394 °C, when it is known as γ-iron, or austenite. At 912 °C the crystal structure again becomes bcc as α-iron(Sony VAIO VGN-AW230J/H battery), or ferrite, is formed, and at 770 °C (the Curie point, Tc) iron becomes magnetic. As the iron passes through the Curie temperature there is no change in crystalline structure, but there is a change in "domain structure", where each domain contains iron atoms with a particular electronic spin. In unmagnetized iron, all the electronic spins of the atoms within one domain are in the same direction(Sony VAIO VGN-AW235J/B battery); the neighboring domains point in various directions and thus cancel out. In magnetized iron, the electronic spins of all the domains are aligned, so that the magnetic effects of neighboring domains reinforce each other. Although each domain contains billions of atoms, they are very small, about 10 micrometres across(Sony VAIO VGN-AW270Y/Q battery).[10] At pressures above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ε-iron; the higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure. The β-phase, if it exists, would appear at pressures of at least 50 GPa and temperatures of at least 1500 K(Sony VAIO VGN-AW31M/H battery); it has been thought to have an orthorhombic or a double hcp structure.[9]Iron is of greatest importance when mixed with certain other metals and with carbon to form steels. There are many types of steels, all with different properties, and an understanding of the properties of the allotropes of iron is key to the manufacture of good quality steels(Sony VAIO VGN-AW31S/B battery).α-iron, also known as ferrite, is the most stable form of iron at normal temperatures. It is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C).[11]Above 912 °C and up to 1400 °C α-iron undergoes a phase transition from bcc to the fcc configuration of γ-iron, also called austenite. This is similarly soft and metallic but can dissolve considerably more carbon (Sony VAIO VGN-AW31XY/Q battery)(as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of stainless steel used for making cutlery, and hospital and food-service equipment.[10]The high-pressure phases of iron are important as endmember models for the solid parts of planetary cores. The inner core of the Earth is generally assumed to consist essentially of an iron-nickel alloy with ε (or β) structure(Sony VAIO VGN-AW31ZJ/B battery).The melting point of iron is experimentally well constrained for pressures up to approximately 50 GPa. For higher pressures, different studies placed the γ-ε-liquid triple point at pressures differing by tens of gigapascals and yielded differences of more than 1000 K for the melting point(Sony VAIO VGN-AW41JF/H battery). Generally speaking, molecular dynamics computer simulations of iron melting and shock wave experiments suggest higher melting points and a much steeper slope of the melting curve than static experiments carried out in diamond anvil cells.[12][edit]IsotopesMain article: Isotopes of ironNaturally occurring iron consists of four stable isotopes: 5.845% of 54Fe, 91.754% of 56Fe, 2.119% of 57Fe and 0.282% of 58Fe(Sony VAIO VGN-AW41JF battery). Of these stable isotopes, only 57Fe has a nuclear spin (−1/2). The nuclide 54Fe is predicted to undergo double beta decay, but this process had never been observed experimentally for these nuclei, and only the lower limit on the half-life was established: t1/2>3.1×1022 years(Sony VAIO VGN-AW41MF/H battery).60Fe is an extinct radionuclide of long half-life (2.6 million years).[13] It is not found on Earth, but its ultimate decay product forms part of the natural abundance of the stable nuclide nickel-60.Much of the past work on measuring the isotopic composition of Fe has focused on determining 60Fe variations due to processes accompanying nucleosynthesis(Sony VAIO VGN-AW41MF battery) (i.e., meteorite studies) and ore formation. In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth and planetary science communities, although applications to biological and industrial systems are beginning to emerge(Sony VAIO VGN-AW41XH/Q battery).[14]The most abundant iron isotope 56Fe is of particular interest to nuclear scientists as it represents the most common endpoint of nucleosynthesis. It is often cited, falsely, as the isotope of highest binding energy, a distinction which actually belongs to nickel-62.[15] Since 56Ni is easily produced from lighter nuclei in the alpha process in nuclear reactions in supernovae (Sony VAIO VGN-AW41ZF/B battery) (see silicon burning process), nickel-56 (14 alpha particles) is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle would result in zinc-60, which requires a great deal more energy. This nickel-56, which has a half-life of about 6 days, is therefore made in quantity in these stars(Sony VAIO VGN-AW41ZF battery), but soon decays by two successive positron emissions within supernova decay products in the supernova remnant gas cloud, first to radioactive cobalt-56, and then stable iron-56. This last nuclide is therefore common in the universe, relative to other stable metals of approximately the same atomic weight( SONY Vaio VGN-NS38M Battery) .In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Ni, the daughter product of 60Fe, and the abundance of the stable iron isotopes could be found which is evidence for the existence of 60Fe at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe contributed, together with the energy released by decay of the radionuclide 26Al( SONY Vaio VGN-NS31S Battery) , to the remelting and differentiation of asteroids after their formation 4.6 billion years ago[citation needed]. The abundance of 60Ni present in extraterrestrial material may also provide further insight into the origin of the Solar System and its early history.Nuclei of iron atoms have some of the highest binding energies per nucleon, surpassed only by the nickel isotope 62Ni( SONY Vaio VGN-NS31M Battery) . This is formed by nuclear fusion in stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are unsuitable for this process to be favored. Elemental distribution on Earth greatly favors iron over nickel, and also presumably in supernova element production( SONY Vaio VGN-NS31Z Battery) .[16]Iron-56 is the heaviest stable isotope produced by the alpha process in stellar nucleosynthesis; elements heavier than iron and nickel require a supernova for their formation. Iron is the most abundant element in the core of red giants, and is the most abundant metal in iron meteorites and in the dense metal cores of planets such as Earth( SONY Vaio VGN-NS21Z Battery) .[edit]NucleosynthesisIron is created by extremely large, extremely hot (over 2.5 billion kelvin) stars, through a process called the silicon burning process. It is the heaviest stable element to be produced in this manner. The process starts with the second largest stable nucleus created by silicon burning: calcium( SONY Vaio VGN-NS21M Battery) . One stable nucleus of calcium fuses with one helium nucleus, creating unstable titanium. Before the titanium decays, it can fuse with another helium nucleus, creating unstable chromium. Before the chromium decays, it can fuse with another helium nucleus, creating unstable iron. Before the iron decays, it can fuse with another helium nucleus( SONY Vaio VGN-NS21S Battery) , creating unstable nickel-56. Any further fusion of nickel-56 consumes energy instead of producing energy, so after the production of nickel-56, the star does not produce the energy necessary to keep the core from collapsing. Eventually, the nickel-56 decays to unstable cobalt-56 which, in turn decays to stable iron-56. When the core of the star collapses( SONY Vaio VGN-NS12S Battery) , it creates a Supernova. Supernovas also create additional forms of stable iron via the r-process.[edit]OccurrenceSee also Category: Iron minerals[edit]Planetary occurrenceIron meteorites of similar composition of Earth's inner and outer coreIron is the sixth most abundant element in the Universe, and the most common refractory element.[17] It is formed as the final exothermic stage of stellar nucleosynthesis, by silicon fusion in massive stars. Metallic iron is rarely found on the surface of the Earth because it tends to oxidize( SONY Vaio VGN-NS12M Battery) , but its oxides are pervasive and represent the primary ores. While it makes up about 5% of the Earth's crust, both the Earth's inner and outer core are believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth as a whole. Iron is consequently the most abundant element on Earth, but only the fourth most abundant element in the Earth's crust( SONY Vaio VGN-NS11Z Battery) .[18][19] Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite and magnetite. Large deposits of iron are found in banded iron formations. These geological formations are a type of rock consisting of repeated thin layers of iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shale and chert( SONY Vaio VGN-NS11M Battery) . The banded iron formations are common in the time between 3,700 million years ago and 1,800 million years ago[20][21]About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Although rare, iron meteorites are the main form of natural metallic iron on the Earth's surface.[22] It was proven by Mössbauer spectroscopy that the red color of the surface of Mars is derived from an iron oxide-rich regolith( SONY Vaio VGN-NS11L Battery) .[23][edit]Stocks in use in societyAccording to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of iron in use in society is 2200 kg. Much of this is in more-developed countries (7000–14000 kg per capita) rather than less-developed countries (2000 kg per capita) ( SONY Vaio VGN-NS11J Battery) .[edit]Chemistry and compoundsand reduction in plants and animals.Iron forms compounds mainly in the +2 and +3 oxidation states. Traditionally, iron(II) compounds are called ferrous, and iron(III) compounds ferric. Iron also occurs in higher oxidation states, an example being the purple potassium ferrate (K2FeO4) which contains iron in its +6 oxidation state( SONY Vaio VGN-NS11E Battery) . Iron(IV) is a common intermediate in many in biochemical oxidation reactions.[24][25] Numerous organometallic compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopy( SONY Vaio VGN-NS10L Battery) .[26] There are also many mixed valence compounds that contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue (Fe4(Fe[CN]6)3).[25] The latter is used as the traditional "blue" in blueprints.[27]Hydrated iron(III) chloride, also known as ferric chlorideThe iron compounds produced on the largest scale in industry are iron(II) sulfate (FeSO4·7H2O) and iron(III) chloride (FeCl3)( SONY Vaio VGN-NS10J Battery) . The former is one of the most readily available sources of iron(II), but is less stable to aerial oxidation than Mohr's salt ((NH4)2Fe(SO4)2·6H2O). Iron(II) compounds tend to be oxidized to iron(III) compounds in the air.[25]Unlike many other metals, iron does not form amalgams with mercury. As a result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron( SONY Vaio VGN-NS10E Battery) .[28][edit]Binary compoundsIron reacts with oxygen in the air to form various oxide and hydroxide compounds; the most common are iron(II,III) oxide (Fe3O4), and iron(III) oxide (Fe2O3). Iron(II) oxide also exists, though it is unstable at room temperature. These oxides are the principal ores for the production of iron (see bloomery and blast furnace) ( SONY Vaio VGN-NS38M/W Battery) . They are also used in the production of ferrites, useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS2), also known as fool's gold owing to its golden luster.[25]The binary ferrous and ferric halides are well known, with the exception of ferric iodide. The ferrous halides typically arise from treating iron metal with the corresponding binary halogen acid to give the corresponding hydrated salts( SONY Vaio VGN-NS38M/P Battery) .[25]Fe + 2 HX → FeX2 + H2Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric chloride being the most common:2 Fe + 3 X2 → 2 FeX3 (X = F, Cl, Br)[edit]Coordination and organometallic compoundsSee also: organoiron chemistryPrussian blueSeveral cyanide complexes are known. The most famous example is Prussian blue, (Fe4(Fe[CN]6)3). Potassium ferricyanide and potassium ferrocyanide are also known; the formation of Prussian blue upon reaction with iron(II) and iron(III) respectively forms the basis of a "wet" chemical test( SONY Vaio VGN-NS31Z/W Battery) .[25] Prussian blue is also used as an antidote for thallium and radioactive caesium poisoning.[29][30] Prussian blue can be used in laundry bluing to correct the yellowish tint left by ferrous salts in water.[31]FerroceneSeveral carbonyl compounds of iron are known. The premier iron(0) compound is iron pentacarbonyl, Fe(CO)5, which is used to produce carbonyl iron powder( SONY Vaio VGN-NS31Z/S Battery) , a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives the trinuclear cluster, triiron dodecacarbonyl. Collman's reagent, disodium tetracarbonylferrate, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state( SONY Vaio VGN-NS31Z/P Battery) .[32]Ferrocene is an extremely stable complex. The first sandwich compound, it contains an iron(II) center with two cyclopentadienyl ligands bonded through all ten carbon atoms. This arrangement was a shocking novelty when it was first discovered,[33] but the discovery of ferrocene has led to a new branch of organometallic chemistry( SONY Vaio VGN-NS31S/S Battery) . Ferrocene itself can be used as the backbone of a ligand, e.g. dppf. Ferrocene can itself be oxidized to the ferrocenium cation (Fc+); the ferrocene/ferrocenium couple is often used as a reference in electrochemistry.[34][edit]HistoryMain article: History of ferrous metallurgy[edit]Wrought ironThe symbol for Mars has been used since antiquity to represent iron.The Delhi iron pillar is an example of the iron extraction and processing methodologies of India. The iron pillar at Delhi has withstood corrosion for the last 1600 years( SONY Vaio VGN-NS31M/W Battery) .Iron objects of great age are much rarer than objects made of gold or silver due to the ease of corrosion of iron.[35] Beads made of meteoric iron in 3500 B.C. or earlier were found in Gerzah, Egypt by G. A. Wainwright.[36] The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust has very little to no nickel content( SONY Vaio VGN-NS31M/P Battery) . Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools or whole specimens placed in churches.[36] Items that were likely made of iron by Egyptians date from 2500 to 3000 BC.[35] Iron had a distinct advantage over bronze in warfare implements. It was much harder and more durable than bronze( SONY Vaio VGN-NS21Z/S Battery) , although susceptible to rust. However, this is contested. Hittitologist Trevor Bryce argues that before advanced iron-working techniques were developed in India, cast-iron weapons used by early Mesopotamian armies had a tendency to shatter in combat, due to their high carbon content.[37]The first iron production started in the Middle Bronze Age but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar( SONY Vaio VGN-NS21S/W Battery) , Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 2700 and 3000 BC.[38] The Hittites appear to be the first to understand the production of iron from its ores and regard it highly in their society.[31] They began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC( SONY Vaio VGN-NS21S/S Battery) .[38] The subsequent period is called the Iron Age. Iron smelting, and thus the Iron Age, reached Europe two hundred years later and arrived in Zimbabwe, Africa by the 8th century.[38]Artifacts from smelted iron occur in India from 1800 to 1200 BC,[39] and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus). ( SONY Vaio VGN-NS21M/W Battery) The Book of Genesis, fourth chapter, verse 22 contains the first mention of iron in the Old Testament of the Bible; "Tubal-cain, an instructor of every artificer in brass and iron."[35] Other verses allude to iron mining (Job 28:2), iron used as a stylus (Job 19:24), furnace (Deuteronomy 4:20), chariots (Joshua 17:16) ( SONY Vaio VGN-NS21M/P Battery) , nails (I Chron. 22:3), saws and axes (II Sam. 12:31), and cooking utensils (Ezekiel 4:3).[42] The metal is also mentioned in the New Testament, for example in Acts chapter 12 verse 10, "[Peter passed through] the iron gate that leadeth unto the city" of Antioch.[43] The Quran referred to Iron 1400 years ago( SONY Vaio VGN-NS12S/S Battery) .Iron working was introduced to Greece in the late 11th century BC.[44] The spread of ironworking in Central and Western Europe is associated with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era.[36] The annual iron output of the Roman Empire is estimated at 84,750 t,[45] while the similarly populous Han China produced around 5,000 t. ( SONY Vaio VGN-NS12M/W Battery) During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others including Joseph Hall( SONY Vaio VGN-NS12M/S Battery) .[edit]Cast ironCast iron was first produced in China about 550 BC,[47] but was hardly in Europe until the medieval period.[48][49] During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel( SONY Vaio VGN-NS11Z/S Battery) .Coalbrookdale by Night, 1801. Blast furnaces light the iron making town of Coalbrookdale.Medieval blast furnaces were about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows.[49] Modern blast furnaces have grown much bigger( SONY Vaio VGN-NS11ZR/S Battery) .In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper( SONY Vaio VGN-NS11S/S Battery) . Carbon content in iron wasn't implicated as the reason for the differences in properties of wrought iron, cast iron and steel until the 18th century.[38]Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778( SONY Vaio VGN-NS11SR/S Battery) .[edit]SteelSee also: SteelmakingSteel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Iran were making good steel by 1000 BC.[38] Then improved versions, Wootz steel by India and Damascus steel by China were developed around 300 B.C. and 500 A.D. respectively( SONY Vaio VGN-NS11M/S Battery) . These methods were specialized, and so steel did not become a major commodity until the 1850s.[50]New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century AD. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel( SONY Vaio VGN-NS11MR/S Battery) . In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced.[citation needed][edit]Foundations of modern chemistryAntoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the mass conservation( SONY Vaio VGN-NS11L/S Battery) . Anaerobic oxidation of iron at high temperature can be schematically represented by the following reactions: Fe + H2O → FeO + H22 Fe + 3 H2O → Fe2O3 + 3 H23 Fe + 4 H2O → Fe3O4 + 4 H2[edit]Recent discoveriesdiscovery of Mössbauer effectmany enzymes use iron in the catalytic centerNickel-56 is the natural end product of silicon burning in massive stars. However Nickel-56 decays to cobalt-56 and then to stable iron-56, ultimately making iron the most abundant heavy element produced by that nucleosynthesis( SONY Vaio VGN-NS11J/S Battery) .[51]superconductivity?magnetic effectferrocene[edit]Industrial productionSee also: Iron oreThe production of iron or steel is a process containing two main stages, unless the desired product is cast iron. The first stage is to produce pig iron in a blast furnace. Alternatively, it may be directly reduced. The second is to make wrought iron or steel from pig iron by a further process( SONY Vaio VGN-NS11E/S Battery) .The fining process of smelting iron ore to make wrought iron from pig iron, with the right illustration displaying men working a blast furnace, from the Tiangong Kaiwu encyclopedia, published in 1637 by Song Yingxing.How iron was extracted in the 19th centuryFor a few limited purposes like electromagnet cores, pure iron is produced by electrolysis of a ferrous sulfate solution( SONY Vaio VGN-NS11ER/S Battery) [edit]Blast furnaceMain article: Blast furnaceNinety percent of all mining of metallic ores is for the extraction of iron[citation needed]. Industrially, iron production involves iron ores, principally hematite (nominally Fe2O3) and magnetite (Fe3O4) in a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000 °C. In a blast furnace, iron ore( SONY Vaio VGN-NS115N/S Battery) , carbon in the form of coke, and a flux such as limestone (which is used to remove silicon dioxide impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a massive blast of heated air, about 4 tons per ton of iron,[49] is forced into the furnace at the bottom( SONY Vaio VGN-NS110E/W Battery) .Iron output in 2005In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:2 C + O2 → 2 COThe carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:Fe2O3 + 3 CO → 2 Fe + 3 CO2Some iron in the high-temperature lower region of the furnace reacts directly with the coke( SONY Vaio VGN-NS110E/S Battery) :2 Fe2O3 + 3 C → 4 Fe + 3 CO2The flux is present to melt impurities in the ore, principally silicon dioxide sand and other silicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (calcium-magnesium carbonate). Other fluxes may be used depending on the impurities that need to be removed from the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (also known as quicklime) ( SONY Vaio VGN-NS110E/L Battery) :CaCO3 → CaO + CO2Then calcium oxide combines with silicon dioxide to form a liquid slag.CaO + SiO2 → CaSiO3The slag melts in the heat of the furnace. In the bottom of the furnace, the molten slag floats on top of the denser molten iron, and apertures in the side of the furnace are opened to run off the iron and the slag separately. The iron, once cooled, is called pig iron, while the slag can be used as a material in road construction or to improve mineral-poor soils for agriculture( SONY Vaio VGN-NS10L/S Battery) This heap of iron ore pellets will be used in steel production.In 2005, approximately 1,544 million metric tons of iron ore were produced worldwide. According to the British Geological Survey, China was the top producer of iron ore with at least one quarter world share, followed by Brazil, Australia and India( SONY Vaio VGN-NS10J/S Battery) .[edit]Direct iron reductionSince coke is becoming more regulated due to environmental concerns, alternative methods of processing iron have been developed. One of them is known as direct iron reduction.[49] It reduces iron ore to a powder substance called sponge iron, which is suitable for steelmaking. There are two main reactions that go on in the direct reduction process( SONY Vaio VGN-NS10E/S Battery) :Natural gas is partially oxidized (with heat and a catalyst):2 CH4 + O2 → 2 CO + 4 H2These gases are then treated with iron ore in a furnace, producing solid sponge iron:Fe2O3 + CO + 2 H2 → 2 Fe + CO2 + 2 H2OSilica is removed by adding a flux, i.e. limestone, later.[edit]Further processesPig iron is not pure iron, but has 4–5% carbon dissolved in it with small amounts of other impurities like sulfur, magnesium, phosphorus and manganese. As the carbon is the major impurity, the iron (pig iron) becomes brittle and hard( Sony VAIO VGN-SR94VS battery) . This form of iron, also known as cast iron, is used to cast articles in foundries such as stoves, pipes, radiators, lamp-posts and rails.Alternatively pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including finery forges, puddling furnaces( Sony VAIO VGN-SR59VG battery) , Bessemer converters, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels.The hardness of the steel depends upon its carbon content: the higher the percentage of carbon, the greater the hardness and the lesser the malleability( Sony VAIO VGN-SR59VG/H battery) . The properties of the steel can also be changed by several methods.Annealing involves the heating of a piece of steel to 700–800 °C for several hours and then gradual cooling. It makes the steel softer and more workable.Steel may be hardened by cold working. The metal is bent or hammered into its final shape at a relatively cool temperature( Sony VAIO VGN-SR55TF/B battery) . Cold forging is the stamping of a piece of steel into shape by a heavy press. Wrenches are commonly made by cold forging. Cold rolling, which involves making a thinner but harder sheet, and cold drawing, which makes a thinner but stronger wire, are two other methods of cold working. To harden the steel( Sony VAIO VGN-SR51MF battery) , it is heated to red-hot and then cooled by quenching it in the water. It becomes harder and more brittle. If it is too hardened, it is then heated to a required temperature and allowed to cool. The steel thus formed is less brittle.Heat treatment is another way to harden steel. The steel is heated red-hot, then cooled quickly. The iron carbide molecules are decomposed by the heat( Sony VAIO VGN-SR51MF/W battery) , but do not have time to reform. Since the free carbon atoms are stuck, it makes the steel much harder and stronger than before.[49]Sometimes both toughness and hardness are desired. A process called case hardening may be used. Steel is heated to about 900 °C then plunged into oil or water. Carbon from the oil can diffuse into the steel( Sony VAIO VGN-SR51B battery) , making the surface very hard. The surface cools quickly, but the inside cools slowly, making an extremely hard surface and a durable, resistant inner layer.Iron may be passivated by dipping it into a concentrated nitric acid solution. This forms a protective layer of oxide on the metal, protecting it from further corrosion( Sony VAIO VGN-SR51B/S battery) .[52][edit]Applications[edit]MetallurgicalIron is the most widely used of all the metals, accounting for 95% of worldwide metal production.[citation needed] Its low cost and high strength make it indispensable in engineering applications such as the construction of machinery and machine tools, automobiles, the hulls of large ships, and structural components for buildings( Sony VAIO VGN-SR51B/P battery) . Since pure iron is quite soft, it is most commonly used in the form of steel.Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon[53] and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel from iron ore( Sony VAIO VGN-SR49VN/H battery) . Cast iron contains 2–4% carbon, 1–6% silicon, and small amounts of manganese. Contaminants present in pig iron that negatively affect material properties, such as sulfur and phosphorus, have been reduced to an acceptable level. It has a melting point in the range of 1420–1470 K, which is lower than either of its two main components( Sony VAIO VGN-SR49D battery) , and makes it the first product to be melted when carbon and iron are heated together. Its mechanical properties vary greatly, dependent upon the form carbon takes in the alloy."White" cast irons contain their carbon in the form of cementite, or iron carbide. This hard, brittle compound dominates the mechanical properties of white cast irons( Sony VAIO VGN-SR49D/Q battery) , rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken carbide, a very pale, silvery, shiny material, hence the appellation.In gray iron the carbon exists free as fine flakes of graphite, and also renders the material brittle due to the stress-raising nature of the sharp edged flakes of graphite. A newer variant of gray iron( Sony VAIO VGN-SR49D/J battery) , referred to as ductile iron is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, vastly increasing the toughness and strength of the material.Wrought iron contains less than 0.25% carbon.[53] It is a tough, malleable product, but not as fusible as pig iron( Sony VAIO VGN-SR48J battery) . If honed to an edge, it loses it quickly. Wrought iron is characterized by the presence of fine fibers of slag entrapped in the metal. Wrought iron is more corrosion resistant than steel. It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithing( Sony VAIO VGN-SR48J/J battery) .Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Carbon steel contains 2.0% carbon or less,[54] with small amounts of manganese, sulfur, phosphorus, and silicon. Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium( Sony VAIO VGN-SR48J/B battery) , molybdenum, nickel, tungsten, etc. Their alloy content raises their cost, and so they are usually only employed for specialist uses. One common alloy steel, though, is stainless steel. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA' or high-strength( Sony VAIO VGN-SR46TD/B battery) , low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal cost.Apart from traditional applications, iron is also used for protection from ionizing radiation. Although it is lighter than another traditional protection material, lead, it is much stronger mechanically. The attenuation of radiation as a function of energy is shown in the graph( Sony VAIO VGN-SR46MD/B battery) .The main disadvantage of iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some way. Painting, galvanization, passivation, plastic coating and bluing are all used to protect iron from rust by excluding water and oxygen or by cathodic protection( Sony VAIO VGN-SR46GD battery) .[edit]Of compoundsAlthough its metallurgical role is dominant in terms of amounts, iron compounds are pervasive in industry as well being used in many niche uses. Iron catalysts are traditionally used in the Haber-Bosch Process for the production of ammonia and the Fischer-Tropsch process for conversion of carbon monoxide to hydrocarbons for fuels and lubricants( Sony VAIO VGN-SR45T/W battery) .[55] Powdered iron in an acidic solvent was used in the Bechamp reduction the reduction of nitrobenzene to aniline.[56]Iron(III) chloride finds use in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an etchant for copper in the manufacture of printed circuit boards( Sony VAIO VGN-SR45T/P battery) .[57] It can also be dissolved in alcohol to form tincture of iron.[31] The other halides tend to be limited to laboratory uses.Iron(II) sulfate is used as a precursor to other iron compounds. It is also used to reduce chromate in cement. It is used to fortify foods and treat iron deficiency anemia. These are its main uses( Sony VAIO VGN-SR45T/B battery) . Iron(III) sulfate is used in settling minute sewage particles in tank water. Iron(II) chloride is used as a reducing flocculating agent, in the formation of iron complexes and magnetic iron oxides, and as a reducing agent in organic synthesis.[edit]Biological roleIron is abundant in biology. Iron-proteins are found in all living organisms, ranging from the evolutionarily primitive archaea to humans( Sony VAIO VGN-SR45H battery) . The color of blood is due to the hemoglobin, an iron-containing protein. As illustrated by hemoglobin, iron often is bound to cofactors, e.g. in hemes. The iron-sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Influential theories of evolution have invoked a role for iron sulfides in the iron-sulfur world theory( Sony VAIO VGN-SR45H/P battery) .Structure of Heme b, in the protein additional ligand(s) would be attached to Fe.Iron is a necessary trace element found in nearly all living organisms. Iron-containing enzymes and proteins, often containing heme prosthetic groups, participate in many biological oxidations and in transport. Examples of proteins found in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase( Sony VAIO VGN-SR45H/N battery) .[58][edit]Bioinorganic compoundsThe most commonly-known and studied "bioinorganic" compounds of iron (i.e., iron compounds used in biology) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450. These compounds can transport gases, build enzymes, and be used in transferring electrons( Sony VAIO VGN-SR45H/B battery) . Metalloproteins are a group of proteins with metal ion cofactors. Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP.[edit]Health and dietMain articles: Iron deficiency (medicine) and Human iron metabolismIron is pervasive, but particularly rich sources of dietary iron include red meat, lentils, beans, poultry, fish, leaf vegetables, tofu, chickpeas, black-eyed peas( Sony VAIO VGN-SR41M/W battery) , blackstrap molasses, fortified bread, and fortified breakfast cereals. Iron in low amounts is found in molasses, teff and farina. Iron in meat (heme iron) is more easily absorbed than iron in vegetables.[59] Although some studies suggest that heme/hemoglobin from red meat has effects which may increase the likelihood of colorectal cancer( Sony VAIO VGN-SR41M/S battery) ,[60][61] there is still some controversy,[62] and even a few studies suggesting that there is not enough evidence to support such claims.[63]Iron provided by dietary supplements is often found as iron(II) fumarate, although iron sulfate is cheaper and is absorbed equally well. Elemental iron, or reduced iron, despite being absorbed at only one third to two thirds the efficiency (relative to iron sulfate) ( Sony VAIO VGN-SR41M/P battery) ,[64] is often added to foods such as breakfast cereals or enriched wheat flour. Iron is most available to the body when chelated to amino acids[65] and is also available for use as a common iron supplement. Often the amino acid chosen for this purpose is the cheapest and most common amino acid, glycine, leading to "iron glycinate" supplements( Sony VAIO VGN-SR3CW/B battery) .[66] The Recommended Dietary Allowance (RDA) for iron varies considerably based on age, gender, and source of dietary iron (heme-based iron has higher bioavailability).[67] Infants may require iron supplements if they are bottle-fed cow's milk.[68] Blood donors and pregnant women are at special risk of low iron levels and are often advised to supplement their iron intake( Sony VAIO VGN-SR39XN/S battery) .[69][edit]Uptake and storageIron acquisition poses a problem for aerobic organisms, because ferric iron is poorly soluble near neutral pH. Thus, bacteria have evolved high-affinity sequestering agents called siderophores.After uptake, in cells, iron storage is carefully regulated; "free" iron ions do not exist as such. A major component of this regulation is the protein transferrin( Sony VAIO VGN-SR39VN/S battery) , which binds iron ions absorbed from the duodenum and carries it in the blood to cells.[73] In animals, plants, and fungi, iron is often the metal ion incorporated into the heme complex. Heme is an essential component of cytochrome proteins, which mediate redox reactions, and of oxygen carrier proteins such as hemoglobin, myoglobin, and leghemoglobin( Sony VAIO VGN-SR39D battery) .Inorganic iron contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (involved in the synthesis of ammonia from nitrogen and hydrogen) and hydrogenase. Non-heme iron proteins include the enzymes methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase ( Sony VAIO VGN-SR39D/Q battery) (reduces ribose to deoxyribose; DNA biosynthesis), hemerythrins (oxygen transport and fixation in marine invertebrates) and purple acid phosphatase (hydrolysis of phosphate esters).Iron distribution is heavily regulated in mammals, partly because iron ions have a high potential for biological toxicity.[74][edit]Regulation of uptakeMain article: HepcidinIron uptake is tightly regulated by the human body, which has no regulated physiological means of excreting iron( Sony VAIO VGN-SR39D/J battery) . Only small amounts of iron are lost daily due to mucosal and skin epithelial cell sloughing, so control of iron levels is mostly by regulating uptake.[75] Regulation of iron uptake is impaired in some people as a result of a genetic defect that maps to the HLA-H gene region on chromosome 6( Sony VAIO VGN-SR390NAH battery) . In these people, excessive iron intake can result in iron overload disorders, such as hemochromatosis. Many people have a genetic susceptibility to iron overload without realizing it or being aware of a family history of the problem. For this reason, it is advised that people do not take iron supplements unless they suffer from iron deficiency and have consulted a doctor( Sony VAIO VGN-SR38 battery) . Hemochromatosis is estimated to cause disease in between 0.3 and 0.8% of Caucasians.[76]MRI finds that iron accumulates in the hippocampus of the brains of those with Alzheimer's disease and in the substantia nigra of those with Parkinson disease.[77][edit]Permeable reactive barriersZero-valent iron is the main reactive material for permeable reactive barriers. ( Sony VAIO VGN-SR38/Q battery) [edit]PrecautionsFire diamond for powdered iron metalMain article: Iron poisoningLarge amounts of ingested iron can cause excessive levels of iron in the blood. High blood levels of free ferrous iron react with peroxides to produce free radicals, which are highly reactive and can damage DNA, proteins, lipids, and other cellular components. Thus, iron toxicity occurs when there is free iron in the cell( Sony VAIO VGN-SR38/P battery) , which generally occurs when iron levels exceed the capacity of transferrin to bind the iron. Damage to the cells of the gastrointestinal tract can also prevent them from regulating iron absorption leading to further increases in blood levels. Iron typically damages cells in the heart, liver and elsewhere, which can cause significant adverse effects, including coma( Sony VAIO VGN-SR38/B battery) , metabolic acidosis, shock, liver failure, coagulopathy, adult respiratory distress syndrome, long-term organ damage, and even death.[78] Humans experience iron toxicity above 20 milligrams of iron for every kilogram of mass, and 60 milligrams per kilogram is considered a lethal dose.[79] Overconsumption of iron( Sony VAIO VGN-SR37TN/B battery) , often the result of children eating large quantities of ferrous sulfate tablets intended for adult consumption, is one of the most common toxicological causes of death in children under six.[79] The Dietary Reference Intake (DRI) lists the Tolerable Upper Intake Level (UL) for adults as 45 mg/day. For children under fourteen years old the UL is 40 mg/day( Sony VAIO VGN-SR35T/S battery) .The medical management of iron toxicity is complicated, and can include use of a specific chelating agent called deferoxamine to bind and expel excess iron from the body.
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstancesHP Pavilion dv6-1103au battery.Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is too reactive chemically to occur natively. Instead, it is found combined in over 270 different mineralsHP Pavilion dv6-1102tx battery.[4] The chief ore of aluminium is bauxite.Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materialsHP Pavilion dv6-1102tu battery. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.Despite its prevalence in the environment, aluminium salts are not known to be used by any form of life. In keeping with its pervasiveness, aluminium is well tolerated by plants and animals.[5] Due to their prevalence, potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interestHP Pavilion dv6-1102ax battery.CharacteristicsEtched surface from a high purity (99.9998%) aluminium bar, size 55×37 mmPhysicalAluminium is a relatively soft, durable, lightweight, ductile and malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. It is nonmagnetic and does not easily ignite. A fresh film of aluminium film serves as a good reflector (approximately 92%) of visible light and an excellent reflector (as much as 98%) of medium and far infrared radiationHP Pavilion dv6-1102au battery. The yield strength of pure aluminium is 7–11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa.[6] Aluminium has about one-third the density and stiffness of steel. It is easily machined, cast, drawn and extruded.Aluminium atoms are arranged in a face-centered cubic (fcc) structure. Aluminium has a stacking-fault energy of approximately 200 mJ/m2HP Pavilion dv6-1101tx battery.[7]Aluminium is a good thermal and electrical conductor, having 59% the conductivity of copper, both thermal and electrical. Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 Kelvin and a critical magnetic field of about 100 gauss (10 milliteslas) HP Pavilion dv6-1101tu battery.[8]ChemicalCorrosion resistance can be excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper.[6] This corrosion resistance is also often greatly reduced by aqueous salts, particularly in the presence of dissimilar metalsHP Pavilion dv6-1101so battery.Owing to its resistance to corrosion, aluminium is one of the few metals that retain silvery reflectance in finely powdered form, making it an important component of silver-colored paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3,000–10,000 nm (far IR) regionsHP Pavilion dv6-1101ax battery; in the 400–700 nm visible range it is slightly outperformed by tin and silver and in the 700–3000 (near IR) by silver, gold, and copper.[9]Aluminium is oxidized by water to produce hydrogen and heat:2 Al + 3 H2O → Al2O3 + 3H2This conversion is of interest for the production or storage of energy. Challenges include the expenses associated with the regeneration of the Al metalHP Pavilion dv6-1101au battery.[10]IsotopesMain article: Isotopes of aluminiumAluminium has many known isotopes, whose mass numbers range from 21 to 43; however, only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2×105 y) occur naturally. 27Al has a natural abundance above 99.9%. 26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protonsHP Pavilion dv6-1100sv battery. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scalesHP Pavilion dv6-1100ss battery.[11] Cosmogenic 26Al was first applied in studies of the Moon and meteorites. Meteoroid fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production. After falling to Earth, atmospheric shielding drastically reduces 26Al production, and its decay can then be used to determine the meteorite's terrestrial ageHP Pavilion dv6-1100so battery. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years agoHP Pavilion dv6-1100eo battery.[12]Natural occurrenceSee also: List of countries by bauxite productionStable aluminium is created when hydrogen fuses with magnesium either in large stars or in supernovae.[13]In the Earth's crust, aluminium is the most abundant (8.3% by weight) metallic element and the third most abundant of all elements (after oxygen and silicon).[14] Because of its strong affinity to oxygen, it is almost never found in the elemental stateHP Pavilion dv6-1099ef battery; instead it is found in oxides or silicates. Feldspars, the most common group of minerals in the Earth's crust, are aluminosilicates. Native aluminium metal can only be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes.[15] Native aluminium has been reported in cold seeps in the northeastern continental slope of the South China Sea and Chen et al. HP Pavilion dv6-1090es battery (2011)[16] have proposed a theory of its origin as resulting by reduction from tetrahydroxoaluminate Al(OH)4– to metallic aluminium by bacteria.[16]It also occurs in the minerals beryl, cryolite, garnet, spinel and turquoise. Impurities in Al2O3, such as chromium or iron yield the gemstones ruby and sapphire, respectively.Although aluminium is an extremely common and widespread element, the common aluminium minerals are not economic sources of the metalHP Pavilion dv6-1090eo battery. Almost all metallic aluminium is produced from the ore bauxite (AlOx(OH)3–2x). Bauxite occurs as a weathering product of low iron and silica bedrock in tropical climatic conditions.[17] Large deposits of bauxite occur in Australia, Brazil, Guinea and Jamaica and the primary mining areas for the ore are in Australia, Brazil, China, India, Guinea, Indonesia, Jamaica, Russia and SurinamHP Pavilion dv6-1080es battery.Production and refinementSee also: Category:Aluminium minerals and List of countries by aluminium productionBauxite, a major aluminium ore. The red-brown colour is due to the presence of iron minerals.Aluminium forms strong chemical bonds with oxygen. Compared to most other metals, it is difficult to extract from ore, such as bauxite, due to the high reactivity of aluminum and the high melting point of most of its oresHP Pavilion dv6-1080eq battery. For example, direct reduction with carbon, as is used to produce iron, is not chemically possible because aluminium is a stronger reducing agent than carbon. Indirect carbothermic reduction can be carried out using carbon and Al2O3, which forms an intermediate Al4C3 and this can further yield aluminium metal at a temperature of 1900–2000 °C. This process is still under developmentHP Pavilion dv6-1080el battery; it requires less energy and yields less CO2 than the Hall-Héroult process, the major industrial process for aluminium extraction.[18] Electrolytic smelting of alumina was originally cost-prohibitive in part because of the high melting point of alumina, or aluminium oxide, (about 2,000 °C (3,600 °F)). Many mineralsHP Pavilion dv6-1070eo battery, however, will disolve into a second already molten mineral, even if the temperature of the melt is significantly lower than the melting point of the first mineral. Molten cryolite was discovered to disolve alumina at temperatures signifcanlty lower than the melting point of pure alumina without interfering in the smelting process. In the Hall-Héroult processHP Pavilion dv6-1068el battery, alumina is first disolved into molten cryolite with calcium fluoride and then electolytically reduced to aluminium at a temperature between 950 and 980 °C (1,740 to 1,800 °F). Cryolite is a chemical compound of aluminium and sodium fluorides: (Na3AlF6). Although cryolite is found as a mineral in Greenland, its synthetic form is used in the industry. The aluminium oxide itself is obtained by refining bauxite in the Bayer processHP Pavilion dv6-1066el battery.The electrolytic process replaced the Wöhler process, which involved the reduction of anhydrous aluminium chloride with potassium. Both of the electrodes used in the electrolysis of aluminium oxide are carbon. Once the refined alumina is dissolved in the electrolyte, it disassociates and its ions are free to move around. The reaction at the cathode isHP Pavilion dv6-1062el battery:Al3+ + 3 e− → AlHere the aluminium ion is being reduced. The aluminium metal then sinks to the bottom and is tapped off, usually cast into large blocks called aluminium billets for further processing.At the anode, oxygen is formed:2 O2− → O2 + 4 e−To some extent, the carbon anode is consumed by subsequent reaction with oxygen to form carbon dioxide. The anodes in a reduction cell must therefore be replaced regularly, since they are consumed in the processHP Pavilion dv6-1060ev battery. The cathodes do erode, mainly due to electrochemical processes and metal movement. After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear.World production trend of aluminiumAluminium electrolysis with the Hall-Héroult process consumes a lot of energy, but alternative processes were always found to be less viable economically and/or ecologicallyHP Pavilion dv6-1060es battery. The worldwide average specific energy consumption is approximately 15±0.5 kilowatt-hours per kilogram of aluminium produced (52 to 56 MJ/kg). The most modern smelters achieve approximately 12.8 kW·h/kg (46.1 MJ/kg). (Compare this to the heat of reaction, 31 MJ/kg, and the Gibbs free energy of reaction, 29 MJ/kg.) Reduction line currents for older technologies are typically 100 to 200 kiloamperesHP Pavilion dv6-1060eo battery; state-of-the-art smelters operate at about 350 kA. Trials have been reported with 500 kA cells.[citation needed]The Hall-Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoope process. The process involves the electrolysis of molten aluminium with a sodium, barium and aluminium fluoride electrolyte. The resulting aluminium has a purity of 99.99%.HP Pavilion dv6-1060el batteryElectric power represents about 20% to 40% of the cost of producing aluminium, depending on the location of the smelter. Aluminium production consumes roughly 5% of electricity generated in the U.S.[21] Smelters tend to be situated where electric power is both plentiful and inexpensive, such as the United Arab Emirates with excess natural gas supplies and Iceland and Norway with energy generated from renewable sourcesHP Pavilion dv6-1058el battery. The world's largest smelters of alumina are People's Republic of China, Russia, and Quebec and British Columbia in Canada.[21][22][23]Aluminium output in 2005In 2005, the People's Republic of China was the top producer of aluminium with almost a one-fifth world share, followed by Russia, Canada, and the USA, reports the British Geological SurveyHP Pavilion dv6-1056el battery.Over the last 50 years, Australia has become a major producer of bauxite ore and a major producer and exporter of alumina (before being overtaken by China in 2007).[22][24] Australia produced 62 million tonnes of bauxite in 2005. The Australian deposits have some refining problems, some being high in silica, but have the advantage of being shallow and relatively easy to mineHP Pavilion dv6-1055ee battery.[25]RecyclingAluminium recycling codeMain article: Aluminium recyclingAluminium is theoretically 100% recyclable without any loss of its natural qualities. According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of aluminium in use in society (i.e. in cars, buildings, electronics etc.) is 80 kg. Much of this is in more-developed countries (350–500 kg per capita) HP Pavilion dv6-1053cl batteryrather than less-developed countries (35 kg per capita). Knowing the per capita stocks and their approximate lifespans is important for planning recycling.Recovery of the metal via recycling has become an important facet of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium beverage cans brought it to the public awarenessHP Pavilion dv6-1050us battery.Recycling involves melting the scrap, a process that requires only 5% of the energy used to produce aluminium from ore, though a significant part (up to 15% of the input material) is lost as dross (ash-like oxide).[26] The dross can undergo a further process to extract aluminiumHP Pavilion dv6-1050et battery.In Europe aluminium experiences high rates of recycling, ranging from 42% of beverage cans, 85% of construction materials and 95% of transport vehicles.[27]Recycled aluminium is known as secondary aluminium, but maintains the same physical properties as primary aluminium. Secondary aluminium is produced in a wide range of formats and is employed in 80% of alloy injectionsHP Pavilion dv6-1050ep battery. Another important use is for extrusion.White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium that can be extracted industrially.[28] The process produces aluminium billets, together with a highly complex waste material. This waste is difficult to manageHP Pavilion dv6-1050eo battery. It reacts with water, releasing a mixture of gases (including, among others, hydrogen, acetylene, and ammonia), which spontaneously ignites on contact with air;[29] contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, the waste has found use as a filler in asphalt and concreteHP Pavilion dv6-1050en battery.[30]CompoundsOxidation state +3The vast majority of compounds, including all Al-containing minerals and all commercially significant aluminium compounds, feature aluminium in the oxidation state 3+. The coordination number of such compounds varies, but generally Al3+ is six-coordinate or tetracoordinate. Almost all compounds of aluminium(III) are colorlessHP Pavilion dv6-1050ei battery.[14]HalidesAll four trihalides are well known. Unlike the structures of the three heavier trihalides, aluminium fluoride (AlF3) features six-coordinate Al. The octahedral coordination environment for AlF3 is related to the compactness of fluoride ion, six of which can fit around the small Al3+ centre. AlF3 sublimes (with cracking) at 1,291 °C (2,356 °F) HP Pavilion dv6-1050ef battery. With heavier halides, the coordination numbers are lower. The other trihalides are dimeric or polymeric with tetrahedral Al centers. These materials are prepared by treating aluminium metal with the halogen, although other methods exist. Acidification of the oxides or hydroxides affords hydrates. In aqueous solution, the halides often form mixturesHP Pavilion dv6-1046el battery, generally containing six-coordinate Al centres, which are feature both halide and aquo ligands. When aluminium and fluoride are together in aqueous solution, they readily form complex ions such as [AlF(H2O)5]2+, AlF3(H2O)3, and [AlF6]3−. In the case of chloride, polyaluminium clusters are formed such as [Al13O4(OH)24(H2O)12]7+HP Pavilion dv6-1045ez battery.Oxide and hydroxidesAluminium forms one stable oxide, known by its mineral name corundum. Sapphire and ruby are impure corundum contaminated with trace amounts of other metals. The two oxide-hydroxides (AlO(OH) are boehmite and diaspore. There are three trihydroxides: bayerite, gibbsiteHP Pavilion dv6-1045eo battery, and nordstrandite, which differ in their crystalline structure (polymorphs). Most are produced from ores by a variety of wet processes using acid and base. Heating the hydroxides leads to formation of corundrum. These materials are of central importance to the production of aluminium and are themselves extremely usefulHP Pavilion dv6-1045ei battery.Carbide, nitride, and related materialsAluminium carbide (Al4C3) is made by heating a mixture of the elements above 1,000 °C (1,832 °F). The pale yellow crystals consist of tetrahedral aluminium centres. It reacts with water or dilute acids to give methane. The acetylide, Al2(C2)3, is made by passing acetylene over heated aluminiumHP Pavilion dv6-1045ee battery.Aluminium nitride (AlN) is the only nitride known for aluminium. Unlike the oxides it features tetrahedral Al centres. It can be made from the elements at 800 °C (1,472 °F). It is air-stable material with a usefully high thermal conductivity. Aluminium phosphide (AlP) is made similarly, and hydrolyses to give phosphineHP Pavilion dv6-1044el battery:AlP + 3 H2O → Al(OH)3 + PH3Organoaluminium compounds and related hydridesMain article: Organoaluminium compoundStructure of trimethylaluminium, a compound that features five-coordinate carbon.A variety of compounds of empirical formula AlR3 and AlR1.5Cl1.5 exist.[31] These species usually feature tetrahedral Al centres, e.g. "trimethylaluminium" has the formula Al2(CH3)6 (see figure). With large organic groups, triorganoaluminium exist as three-coordinate monomers, such as triisobutylaluminiumHP Pavilion dv6-1042el battery. Such compounds are widely used in industrial chemistry, despite the fact that they are often highly pyrophoric. Few analogues exist between organoaluminium and organoboron compounds except for large organic groups.The important aluminium hydride is lithium aluminium hydride (LiAlH4), which is used in as a reducing agent in organic chemistry. It can be produced from lithium hydride and aluminium trichlorideHP Pavilion dv6-1040ez battery:4 LiH + AlCl3 → LiAlH4 + 3 LiClSeveral useful derivatives of LiAlH4 are known, e.g. Sodium bis(2-methoxyethoxy)dihydridoaluminate. The simplest hydride, aluminium hydride or alane, remains a laboratory curiosity. It is a polymer with the formula (AlH3)n, in contrast to the corresponding boron hydride with the formula (BH3)2HP Pavilion dv6-1040ev battery.Oxidation states +1 and +2Although the great majority of aluminium compounds feature Al3+ centres, compounds with lower oxidation states are known and sometime of significance as precursors to the Al3+ species.Aluminium(I)AlF, AlCl and AlBr exist in the gaseous phase when the tri-halide is heated with aluminium. The composition AlI is unstable at room temperature with respect to the triiodideHP Pavilion dv6-1040el battery:[32]3 AlI → AlI3 + 2 AlA stable derivative of aluminium monoiodide is the cyclic adduct formed with triethylamine, Al4I4(NEt3)4. Also of theoretical interest but only of fleeting existence are Al2O and Al2S is made by heating the normal oxide, Al2O3, with silicon at 1,800 °C (3,272 °F) in a vacuum.[32] Such materials quickly disproportionates to the starting materialsHP Pavilion dv6-1040ek battery.Aluminium(II)Very simple Al(II) compounds are invoked or observed in the reactions of Al metal with oxidants. For example, aluminium monoxide, AlO, has been detected in the gas phase after explosion[33] and in stellar absorption spectra.[34] More thoroughly investigated are compounds of the formula R4Al2 where R is a large organic ligandHP Pavilion dv6-1040ei battery.[35]AnalysisThe presence of aluminium can be detected in qualitative analysis using aluminon.ApplicationsGeneral useAluminium is the most widely used non-ferrous metal.[36] Global production of aluminium in 2005 was 31.9 million tonnes. It exceeded that of any other metal except iron (837.5 million tonnes).[37] Forecast for 2012 is 42–45 million tonnes, driven by rising Chinese outputHP Pavilion dv6-1040ed battery.[38]Aluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common aluminium foils and beverage cans are alloys of 92% to 99% aluminium.[39] The main alloying agents are copper, zinc, magnesium, manganese, and silicon (e.g., duralumin) and the levels of these other metals are in the range of a few percent by weightHP Pavilion dv6-1040eb battery.[40]Household aluminium foilAluminium-bodied Austin "A40 Sports" (circa 1951)Aluminium slabs being transported from a smelterSome of the many uses for aluminium metal are in:Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, etc.) as sheet, tube, castings, etc.Packaging (cans, foil, etc.)Construction (windows, doors, siding, building wire, etc.).[41]A wide range of household items, from cooking utensils to baseball bats, watches.[42]Street lighting poles, sailing ship masts, walking poles, etcHP Pavilion dv6-1038ca battery.Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment.Electrical transmission lines for power distributionMKM steel and Alnico magnetsSuper purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.Heat sinks for electronic appliances such as transistors and CPUs.Substrate material of metal-core copper clad laminates used in high brightness LED lightingHP Pavilion dv6-1030us battery.Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.Aluminium can be reacted with hydrochloric acid or with sodium hydroxide to produce hydrogen gas.A variety of countries, including France, Italy, Poland, Finland, Romania, Israel, and the former Yugoslavia, have issued coins struck in aluminium or aluminium-copper alloys. HP Pavilion dv6-1030eq batterySome guitar models sports aluminium diamond plates on the surface of the instruments, usually either chrome or black. Kramer Guitars and Travis Bean are both known for having produced guitars with necks made of aluminium, which gives the instrument a very distinct soundHP Pavilion dv6-1030eo battery.Aluminium is usually alloyed – it is used as pure metal only when corrosion resistance and/or workability is more important than strength or hardness. A thin layer of aluminium can be deposited onto a flat surface by physical vapour deposition or (very infrequently) chemical vapour deposition or other chemical means to form optical coatings and mirrorsHP Pavilion dv6-1030em battery.Aluminium compoundsBecause aluminium is abundant and most of its derivative exhibit low toxicity, the compounds of aluminium enjoy wide and sometimes large-scale applications.AluminaMain article: Aluminium oxideAluminium oxide (Al2O3) and the associated oxy-hydroxides and trihydroxides are produced or extracted from minerals on a large scaleHP Pavilion dv6-1030ef battery. The great majority of this material is converted to metallic aluminium. About 10% of the production capacity is used for other applications. A major use is as an absorbent, for example alumina will remove water from hydrocarbons, to enable subsequent processes that are poisoned by moisture. Aluminium oxides are common catalysts for industrial processesHP Pavilion dv6-1030ed battery, e.g. the Claus process for converting hydrogen sulfide to sulfur in refineries and for the alkylation of amines. Many industrial catalysts are "supported", meaning generally that an expensive catalyst (e.g., platinum) is dispersed over a high surface area material such as alumina. Being a very hard material (Mohs hardness 9) HP Pavilion dv6-1030ec battery, alumina is widely used as an abrasive and the production of applications that exploit its inertness, e.g., in high pressure sodium lamps.SulfatesSeveral sulfates of aluminium find applications. Aluminium sulfate (Al2(SO4)3(H2O)18) is produced on the annual scale of several billions of kilograms. About half of the production is consumed in water treatment. The next major application is in the manufacture of paper. It is also used as a mordantHP Pavilion dv6-1030ca battery, in fire extinguisher, as a food additive, in fireproofing, and in leather tanning. Aluminium ammonium sulfate, which is also called ammonium alum, (NH4)Al(SO4)2·12H2O, is used as a mordant and in leather tanning.[5] Aluminium potassium sulfate ([Al(K)](SO4)2)(H2O)12 is used similarly. The consumption of both alums is decliningHP Pavilion dv6-1027ef battery.ChloridesAluminium chloride (AlCl3) is used in petroleum refining and in the production of synthetic rubber and polymers. Although it has a similar name, aluminium chlorohydrate has fewer and very different applications, e.g. as a hardening agent and an antiperspirant. It is an intermediate in the production of aluminium metalHP Pavilion dv6-1025ez battery.Niche compoundsGiven the scale of aluminium compounds, a small scale application could still involve thousands of tonnes. One of the many compounds used at this intermediate level include aluminium acetate, a salt used in solution as an astringent. Aluminium borate (Al2O3·B2O3) is used in the production of glass and ceramicsHP Pavilion dv6-1025ei battery. Aluminium fluorosilicate (Al2(SiF6)3) is used in the production of synthetic gemstones, glass and ceramic. Aluminium phosphate (AlPO4) is used in the manufacture: of glass and ceramic, pulp and paper products, cosmetics, paints and varnishes and in making dental cement. Aluminium hydroxide (Al(OH)3) is used as an antacid, as a mordant, in water purificationHP Pavilion dv6-1025ef battery, in the manufacture of glass and ceramic and in the waterproofing of fabrics. Lithium aluminium hydride is a powerful reducing agent used in organic chemistry. Organoaluminiums are used as Lewis acids and cocatalysts. For example, methylaluminoxane is a cocatalyst for Ziegler-Natta olefin polymerization to produce vinyl polymers such as polyetheneHP Pavilion dv6-1023em battery.Aluminium alloys in structural applicationsMain article: Aluminium alloyAluminium foamAluminium alloys with a wide range of properties are used in engineering structures. Alloy systems are classified by a number system (ANSI) or by names indicating their main alloying constituents (DIN and ISO).The strength and durability of aluminium alloys vary widely, not only as a result of the components of the specific alloy, but also as a result of heat treatments and manufacturing processesHP Pavilion dv6-1023ef battery. A lack of knowledge of these aspects has from time to time led to improperly designed structures and gained aluminium a bad reputation.One important structural limitation of aluminium alloys is their fatigue strength. Unlike steels, aluminium alloys have no well-defined fatigue limit, meaning that fatigue failure eventually occurs, under even very small cyclic loadings. This implies that engineers must assess these loads and design for a fixed life rather than an infinite lifeHP Pavilion dv6-1022el battery.Another important property of aluminium alloys is their sensitivity to heat. Workshop procedures involving heating are complicated by the fact that aluminium, unlike steel, melts without first glowing red. Forming operations where a blow torch is used therefore require some expertise, since no visual signs reveal how close the material is to melting. Aluminium alloysHP Pavilion dv6-1020et battery, like all structural alloys, also are subject to internal stresses following heating operations such as welding and casting. The problem with aluminium alloys in this regard is their low melting point, which make them more susceptible to distortions from thermally induced stress relief. Controlled stress relief can be done during manufacturing by heat-treating the parts in an ovenHP Pavilion dv6-1020eg battery, followed by gradual cooling—in effect annealing the stresses.The low melting point of aluminium alloys has not precluded their use in rocketry; even for use in constructing combustion chambers where gases can reach 3500 K. The Agena upper stage engine used a regeneratively cooled aluminium design for some parts of the nozzle, including the thermally critical throat regionHP Pavilion dv6-1020el battery.Another alloy of some value is aluminium bronze (Cu-Al alloy).HistoryThe statue of the Anteros (commonly mistaken for either The Angel of Christian Charity or Eros) in Piccadilly Circus, London, was made in 1893 and is one of the first statues to be cast in aluminium.Ancient Greeks and Romans used aluminium salts as dyeing mordants and as astringents for dressing wounds; alum is still used as a stypticHP Pavilion dv6-1020ek battery. In 1761, Guyton de Morveau suggested calling the base alum alumine. In 1808, Humphry Davy identified the existence of a metal base of alum, which he at first termed alumium and later aluminum (see etymology section, below).The metal was first produced in 1825 in an impure form by Danish physicist and chemist Hans Christian Ørsted. He reacted anhydrous aluminium chloride with potassium amalgam, yielding a lump of metal looking similar to tinHP Pavilion dv6-1020ei battery.[45] Friedrich Wöhler was aware of these experiments and cited them, but after redoing the experiments of Ørsted he concluded that this metal was pure potassium. He conducted a similar experiment in 1827 by mixing anhydrous aluminium chloride with potassium and yielded aluminium.[45] Wöhler is generally credited with isolating aluminium (Latin alumen, alum) HP Pavilion dv6-1020ed battery, but also Ørsted can be listed as its discoverer.[46] Further, Pierre Berthier discovered aluminium in bauxite ore and successfully extracted it.[47] Frenchman Henri Etienne Sainte-Claire Deville improved Wöhler's method in 1846, and described his improvements in a book in 1859, chief among these being the substitution of sodium for the considerably more expensive potassium. HP Pavilion dv6-1020ec battery Deville likely also conceived the idea of the electrolysis of aluminium oxide dissolved in cryolite; Charles Martin Hall and Paul Héroult might have developed the more practical process after Deville.Before the Hall-Héroult process was developed in the late 1880s, aluminium was exceedingly difficult to extract from its various ores. This made pure aluminium more valuable than goldHP Pavilion dv6-1018el battery.[49] Bars of aluminium were exhibited at the Exposition Universelle of 1855.[50] Napoleon III, Emperor of France, is reputed to have given a banquet where the most honoured guests were given aluminium utensils, while the others made do with gold.[51][52]Aluminium was selected as the material to be used for the 100 ounce (2.8 kg) capstone of the Washington Monument in 1884, a time when one ounce (30 grams) cost the daily wage of a common worker on the projectHP Pavilion dv6-1001et battery;[53] The capstone, which was set in place on December 6, 1884, in an elaborate dedication ceremony, was the largest single piece of aluminium cast at the time, when aluminium was as expensive as silver.[53]The Cowles companies supplied aluminium alloy in quantity in the United States and England using smelters like the furnace of Carl Wilhelm Siemens by 1886. HP Pavilion dv6-1001tx batteryCharles Martin Hall of Ohio in the U.S. and Paul Héroult of France independently developed the Hall-Héroult electrolytic process that made extracting aluminium from minerals cheaper and is now the principal method used worldwide. Hall's process,[57] in 1888 with the financial backing of Alfred E. Hunt, started the Pittsburgh Reduction Company today known as AlcoaHP Pavilion dv6-1001xx battery. Héroult's process was in production by 1889 in Switzerland at Aluminium Industrie, now Alcan, and at British Aluminium, now Luxfer Group and Alcoa, by 1896 in Scotland.[58]By 1895, the metal was being used as a building material as far away as Sydney, Australia in the dome of the Chief Secretary's BuildingHP Pavilion dv6-1002tx battery.Many navies have used an aluminium superstructure for their vessels; the 1975 fire aboard USS Belknap that gutted her aluminium superstructure, as well as observation of battle damage to British ships during the Falklands War, led to many navies switching to all steel superstructures. The Arleigh Burke class was the first such U.S. ship, being constructed entirely of steelHP Pavilion dv6-1003tx battery.Aluminium wire was once widely used for domestic electrical wiring. Owing to corrosion-induced failures, a number of fires resulted. This discontinuation thus illustrates one failed application of the otherwise highly useful metal.EtymologyTwo variants of the metal's name are in current use, aluminium and aluminum (besides the obsolete alumium) HP Pavilion dv6-1004tx battery. The International Union of Pure and Applied Chemistry (IUPAC) adopted aluminium as the standard international name for the element in 1990 but, three years later, recognized aluminum as an acceptable variant. Hence their periodic table includes both.[59] IUPAC prefers the use of aluminium in its internal publications, although nearly as many IUPAC publications use the spelling aluminumHP Pavilion dv6-1005ea battery.[60]Most countries use the spelling aluminium. In the United States, the spelling aluminum predominates.[14][61] The Canadian Oxford Dictionary prefers aluminum, whereas the Australian Macquarie Dictionary prefers aluminium. In 1926, the American Chemical Society officially decided to use aluminum in its publications; American dictionaries typically label the spelling aluminium as a British variantHP Pavilion dv6-1005ez battery.The name aluminium derives from its status as a base of alum. It is borrowed from Old French; its ultimate source, alumen, in turn is a Latin word that literally means "bitter salt".[62]The earliest citation given in the Oxford English Dictionary for any word used as a name for this element is alumium, which British chemist and inventor Humphry Davy employed in 1808 for the metal he was trying to isolate electrolytically from the mineral aluminaHP Pavilion dv6-1005tx battery. The citation is from the journal Philosophical Transactions of the Royal Society of London: "Had I been so fortunate as to have obtained more certain evidences on this subject, and to have procured the metallic substances I was in search of, I should have proposed for them the names of silicium, alumium, zirconium, and glucium." HP Pavilion dv6-1006tx batteryDavy settled on aluminum by the time he published his 1812 book Chemical Philosophy: "This substance appears to contain a peculiar metal, but as yet Aluminum has not been obtained in a perfectly free state, though alloys of it with other metalline substances have been procured sufficiently distinct to indicate the probable nature of aluminaHP Pavilion dv6-1007tx battery."[65] But the same year, an anonymous contributor to the Quarterly Review, a British political-literary journal, in a review of Davy's book, objected to aluminum and proposed the name aluminium, "for so we shall take the liberty of writing the word, in preference to aluminum, which has a less classical sound." HP Pavilion dv6-1008tx batteryThe -ium suffix conformed to the precedent set in other newly discovered elements of the time: potassium, sodium, magnesium, calcium, and strontium (all of which Davy isolated himself). Nevertheless, -um spellings for elements were not unknown at the time, as for example platinum, known to Europeans since the 16th centuryHP Pavilion dv6-1009el battery, molybdenum, discovered in 1778, and tantalum, discovered in 1802. The -um suffix is consistent with the universal spelling alumina for the oxide, as lanthana is the oxide of lanthanum, and magnesia, ceria, and thoria are the oxides of magnesium, cerium, and thorium respectively.The spelling used throughout the 19th century by most U.S. chemists was aluminium, but common usage is less clearHP Pavilion dv6-1009tx battery.[67] The aluminum spelling is used in the Webster's Dictionary of 1828. In his advertising handbill for his new electrolytic method of producing the metal 1892, Charles Martin Hall used the -um spelling, despite his constant use of the -ium spelling in all the patents[57] he filed between 1886 and 1903HP Pavilion dv6-1010ea battery.[68] It has consequently been suggested that the spelling reflects an easier to pronounce word with one fewer syllable, or that the spelling on the flier was a mistake. Hall's domination of production of the metal ensured that the spelling aluminum became the standard in North America; the Webster Unabridged Dictionary of 1913, though, continued to use the -ium versionHP Pavilion dv6-1010ed battery.Health concernsNFPA 704000Fire diamond for aluminium shotDespite its natural abundance, aluminium has no known function in biology. It is remarkably nontoxic, aluminium sulfate having an LD50 of 6207 mg/kg (oral, mouse), which corresponds to 500 grams for a 80 kg person.[5] Despite the extremely low acute toxicity, the health effects of aluminium are of interest in view of the widespread occurrence of the element in the environment and in commerceHP Pavilion dv6-1010et battery.Some toxicity can be traced to deposition in bone and the central nervous system, which is particularly increased in patients with reduced renal function. Because aluminium competes with calcium for absorption, increased amounts of dietary aluminium may contribute to the reduced skeletal mineralization (osteopenia) observed in preterm infants and infants with growth retardationHP Pavilion dv6-1010tx battery. In very high doses, aluminium can cause neurotoxicity, and is associated with altered function of the blood-brain barrier.[69] A small percentage of people are allergic to aluminium and experience contact dermatitis, digestive disorders, vomiting or other symptoms upon contact or ingestion of products containing aluminiumHP Pavilion dv6-1011tx battery, such as deodorants or antacids. In those without allergies, aluminium is not as toxic as heavy metals, but there is evidence of some toxicity if it is consumed in excessive amounts.[70] Although the use of aluminium cookware has not been shown to lead to aluminium toxicity in generalHP Pavilion dv6-1012tx battery, excessive consumption of antacids containing aluminium compounds and excessive use of aluminium-containing antiperspirants provide more significant exposure levels. Studies have shown that consumption of acidic foods or liquids with aluminium significantly increases aluminium absorption,[71] and maltol has been shown to increase the accumulation of aluminium in nervous and osseus tissueHP Pavilion dv6-1013ea battery.[72] Furthermore, aluminium increases estrogen-related gene expression in human breast cancer cells cultured in the laboratory.[73] The estrogen-like effects of these salts have led to their classification as a metalloestrogen.The effects of aluminium in antiperspirants has been examined over the course of decades with little evidence of skin irritationHP Pavilion dv6-1013tx battery.[5] Nonetheless, its occurrence in antiperspirants, dyes (such as aluminium lake), and food additives is controversial in some quarters. Although there is little evidence that normal exposure to aluminium presents a risk to healthy adults,[74] some studies point to risks associated with increased exposure to the metal.[75] Aluminium in food may be absorbed more than aluminium from waterHP Pavilion dv6-1016ez battery.[76] Some researchers have expressed concerns that the aluminium in antiperspirants may increase the risk of breast cancer,[77] and aluminium has controversially been implicated as a factor in Alzheimer's disease.[78] The Camelford water pollution incident involved a number of people consuming aluminium sulfateHP Pavilion dv6-6091nr battery. Investigations of the long-term health effects are still ongoing, but elevated brain aluminium concentrations have been found in post-mortem examinations of victims, and further research to determine if there is a link with cerebral amyloid angiopathy has been commissionedHP Pavilion dv6-6090us battery.[79]According to The Alzheimer's Society, the overwhelming medical and scientific opinion is that studies have not convincingly demonstrated a causal relationship between aluminium and Alzheimer's disease.[80] Nevertheless, some studies, such as those on the PAQUID cohort,[81] cite aluminium exposure as a risk factor for Alzheimer's diseaseHP Pavilion dv6-6090sf battery. Some brain plaques have been found to contain increased levels of the metal.[82] Research in this area has been inconclusive; aluminium accumulation may be a consequence of the disease rather than a causal agent. In any event, if there is any toxicity of aluminium, it must be via a very specific mechanismHP Pavilion dv6-6087eg battery, since total human exposure to the element in the form of naturally occurring clay in soil and dust is enormously large over a lifetime.[83][84] Scientific consensus does not yet exist about whether aluminium exposure could directly increase the risk of Alzheimer's disease.[80]Effect on plantsAluminium is primary among the factors that reduce plant growth on acid soils. Although it is generally harmless to plaHP Pavilion dv6-6063sf batteryOrigin and characteristics[edit]Physical and chemical propertiesElemental magnesium is a fairly strong, silvery-white, light-weight metal (two thirds the density of aluminium). It tarnishes slightly when exposed to air, although unlike the alkali metals, storage in an oxygen-free environment is unnecessary because magnesium is protected by a thin layer of oxide that is fairly impermeable and difficult to removeHP Pavilion dv6-6054sf battery. Like its lower periodic table group neighbor calcium, magnesium reacts with water at room temperature, though it reacts much more slowly than calcium. When submerged in water, hydrogen bubbles will almost unnoticeably begin to form on the surface of the metal, though if powdered it will react much more rapidlyHP Pavilion dv6-6054ef battery. The reaction will occur faster with higher temperatures (see precautions). Magnesium's ability to react with water can be harnessed to produce energy and run a magnesium-based engine. Magnesium also reacts exothermically with most acids, such as hydrochloric acid (HCl). As with aluminium, zinc and many other metals, the reaction with hydrochloric acid produces the chloride of the metal and releases hydrogen gasHP Pavilion dv6-6051xx battery.Magnesium is a highly flammable metal, but while it is easy to ignite when powdered or shaved into thin strips, it is difficult to ignite in mass or bulk. Once ignited, it is difficult to extinguish, being able to burn in nitrogen (forming magnesium nitride), carbon dioxide (forming magnesium oxide and carbon) and water (forming magnesium oxide and hydrogen) HP Pavilion dv6-6051sf battery. This property was used in incendiary weapons used in the firebombing of cities in World War II, the only practical civil defense being to smother a burning flare under dry sand to exclude the atmosphere. On burning in air, magnesium produces a brilliant white light which includes strong ultraviolet. Thus magnesium powder (flash powder) was used as a source of illumination in the early days of photographyHP Pavilion dv6-6042sf battery. Later, magnesium ribbon was used in electrically ignited flash bulbs. Magnesium powder is used in the manufacture of fireworks and marine flares where a brilliant white light is required. Flame temperatures of magnesium and magnesium alloys can reach 3,100 °C (3,370 K; 5,610 °F),[7] although flame height above the burning metal is usually less than 300 mm (12 in) HP Pavilion dv6-6029tx battery.[8] Magnesium may be used as an ignition source for thermite, an otherwise difficult to ignite mixture of aluminium and iron oxide powder.Magnesium compounds are typically white crystals. Most are soluble in water, providing the sour-tasting magnesium ion Mg2+. Small amounts of dissolved magnesium ion contribute to the tartness and taste of natural waters. Magnesium ion in large amounts is an ionic laxative, and magnesium sulfate HP Pavilion dv6-6027tx battery (common name: Epsom salt) is sometimes used for this purpose. So-called "milk of magnesia" is a water suspension of one of the few insoluble magnesium compounds, magnesium hydroxide. The undissolved particles give rise to its appearance and name. Milk of magnesia is a mild base commonly used as an antacid, which has some laxative side effectHP Pavilion dv6-6026tx battery.[edit]IsotopesMagnesium has three stable isotopes: 24Mg, 25Mg and 26Mg. All are present in significant amounts (see table of isotopes above). About 79% of Mg is 24Mg. The isotope 28Mg is radioactive and in the 1950s to 1970s was made commercially by several nuclear power plants for use in scientific experiments. This isotope has a relatively short half-life (21 hours) and so its use was limited by shipping timesHP Pavilion dv6-6025tx battery.26Mg has found application in isotopic geology, similar to that of aluminium. 26Mg is a radiogenic daughter product of 26Al, which has a half-life of 717,000 years. Large enrichments of stable 26Mg have been observed in the Ca-Al-rich inclusions of some carbonaceous chondrite meteoritesHP Pavilion dv6-6024tx battery. The anomalous abundance of 26Mg is attributed to the decay of its parent 26Al in the inclusions. Therefore, the meteorite must have formed in the solar nebula before the 26Al had decayed. Hence, these fragments are among the oldest objects in the solar system and have preserved information about its early historyHP Pavilion dv6-6023tx battery.It is conventional to plot 26Mg/24Mg against an Al/Mg ratio. In an isochron dating plot, the Al/Mg ratio plotted is27Al/24Mg. The slope of the isochron has no age significance, but indicates the initial 26Al/27Al ratio in the sample at the time when the systems were separated from a common reservoir.[edit]CreationMagnesium is produced in stars larger than 3 solar masses by fusing helium and neon in the alpha process at temperatures above 600 megakelvinsHP Pavilion dv6-6022eg battery.[edit]OccurrenceSee also Category: Magnesium mineralsCountry 2010 production(tonnes)[9]China 650,000Russia 40,000Israel 30,000Kazakhstan 20,000Brazil 16,000Ukraine 2,000Serbia 2,000Although magnesium is found in over 60 minerals, only dolomite, magnesite, brucite, carnallite, talc, and olivine are of commercial importance.The Mg2+ cation is the second most abundant cation in seawater (occurring at about 12% of the mass of sodium there), which makes seawater and sea-salt an attractive commercial source of Mg. To extract the magnesium, calcium hydroxide is added to seawater to form magnesium hydroxide precipitateHP Pavilion dv6-6013tu battery.MgCl2 + Ca(OH)2 → Mg(OH)2 + CaCl2Magnesium hydroxide (brucite) is insoluble in water so it can be filtered out, and reacted with hydrochloric acid to obtain concentrated magnesium chloride.Mg(OH)2 + 2 HCl → MgCl2 + 2 H2OFrom magnesium chloride, electrolysis produces magnesium.In the United States, magnesium is principally obtained by electrolysis of fused magnesium chloride from brines, wells, and sea water. At the cathode, the Mg2+ ion is reduced by two electrons to magnesium metalHP Pavilion dv6-6013cl battery:Mg2+ + 2 e− → MgAt the anode, each pair of Cl− ions is oxidized to chlorine gas, releasing two electrons to complete the circuit:2 Cl− → Cl2 (g) + 2 e−The United States has traditionally been the major world supplier of this metal, supplying 45% of world production even as recently as 1995. Today, the US market share is at 7%, with a single domestic producer left, US Magnesium, a Renco Group company in Utah born from now-defunct MagcorpHP Pavilion dv6-6012tu battery.[10]As of 2005, China has taken over as the dominant supplier, pegged at 60% world market share, which increased from 4% in 1995. Unlike the above-described electrolytic process, China is almost completely reliant on a different method of obtaining the metal from its ores, the silicothermic Pidgeon process (the reduction of the oxide at high temperatures with silicon). HP Pavilion dv6-6011tu battery[edit]HistorySir Humphry DavyThe name magnesium originates from the Greek word for a district in Thessaly called Magnesia. It is related to magnetite and manganese, which also originated from this area, and required differentiation as separate substances. See manganese for this historyHP Pavilion dv6-6008tx battery.Magnesium is the seventh most abundant element in the Earth's crust by mass or molarity.[2] It is found in large deposits of magnesite, dolomite, and other minerals, and in mineral waters, where magnesium ion is soluble. In 1618, a farmer at Epsom in England attempted to give his cows water from a well thereHP Pavilion dv6-6008sa battery. The cows refused to drink because of the water's bitter taste, but the farmer noticed that the water seemed to heal scratches and rashes. The substance became known as Epsom salts and its fame spread; it was eventually recognized to be hydrated magnesium sulfate, MgSO4.The metal itself was first produced by Sir Humphry Davy in England in 1808 using electrolysis of a mixture of magnesia and mercuric oxideHP Pavilion dv6-6008eg battery.[11] Antoine Bussy prepared it in coherent form in 1831. Davy's first suggestion for a name was magnium,[11] but the name magnesium is now used.[edit]Applications[edit]As metalAn unusual application of magnesium as an illumination source while wakeskating in 1931Magnesium is the third most commonly used structural metal, following iron and aluminium. It has been called the lightest useful metal by The Periodic Table of VideosHP Pavilion dv6-6007tx battery.[12]The main applications of magnesium are, in order: component of aluminium alloys, in die-casting (alloyed with zinc),[13] to remove sulfur in the production of iron and steel, the production of titanium in the Kroll process.[14]Magnesium, in its purest form, can be compared with aluminium, and is strong and light, so it is used in several high volume part manufacturing applications, including automotive and truck componentsHP Pavilion dv6-6007sg battery. Specialty, high-grade car wheels of magnesium alloy are called "mag wheels", although the term is often more broadly misapplied to include aluminum wheels. In 1957, a Chevrolet Corvette SS, designed for racing, was constructed with magnesium body panels. An earlier Mercedes-Benz race car model, the Mercedes-Benz 300 SLR, had a body made from Elektron, a magnesium alloyHP Pavilion dv6-6006ea battery; these cars ran (with successes) at Le Mans, the Mille Miglia, and other world-class race events in 1955 (though one was involved in the single worst accident in auto racing history, in terms of human casualties, at the Le Mans race.) Porsche's all-out quest to decrease the weight of their race cars led to the use of magnesium frames in the famous 917/053 that won Le Mans in 1971HP Pavilion dv6-6005sg battery, and still holds the absolute distance record. The 917/30 Can-Am car also featured a magnesium frame, helping it to make the most of its prodigious 1100–1500 hp. Volkswagen Group has used magnesium in its engine components for many years. For a long time, Porsche used magnesium alloy for its engine blocks due to the weight advantageHP Pavilion dv6-6005eg battery. There is renewed interest in magnesium engine blocks, as featured in the 2006 BMW 325i and 330i models. The BMW engine uses an aluminium alloy insert for the cylinder walls and cooling jackets surrounded by a high-temperature magnesium alloy AJ62A. The application of magnesium AE44 alloy in the 2006 Corvette Z06 engine cradle has advanced the technology of designing robust automotive parts in magnesiumHP Pavilion dv6-6005ea battery. Both these alloys are recent developments in high-temperature low creep magnesium alloys. Mitsubishi Motors also uses magnesium (branded magnesium alloy) for its paddle shifters. The general strategy for such alloys is to form intermetallic precipitates at the grain boundaries, for example by adding mischmetal or calcium.[15] New alloy development and lower costsHP Pavilion dv6-6004sa battery, which are becoming competitive to aluminium, will further the number of automotive applications.[citation needed]Products made of magnesium: firestarter and shavings, sharpener, magnesium ribbonThe second application field of magnesium is electronic devices. Because of low weight, good mechanical and electrical properties, magnesium is widely used for manufacturing of mobile phones, laptop computers, cameras, and other electronic componentsHP Pavilion dv6-6003eg battery.Historically, magnesium was one of the main aerospace construction metals and was used for German military aircraft as early as World War I and extensively for German aircraft in World War II. The Germans coined the name 'Elektron' for magnesium alloy. The term is still used today. Because of perceived hazards with magnesium parts in the event of fireHP Pavilion dv6-6002sg battery, the application of magnesium in the commercial aerospace industry was generally restricted to engine related components. Currently the use of magnesium alloys in aerospace is increasing, mostly driven by the increasing importance of fuel economy and the need to reduce weight.[citation needed] The development and testing of new magnesium alloys continuesHP Pavilion dv6-6002eg battery, notably Elektron 21, which has successfully undergone extensive aerospace testing for suitability in engine, internal and airframe components. The European Community runs three R&D magnesium projects in the Aerospace priority of Six Framework Program.[edit]Niche uses of the metalMagnesium, being available and relatively nontoxic, has variety of uses:Magnesium is flammable, burning at a temperature of approximately 3,100 °C (3,370 K; 5,610 °F) HP Pavilion dv6-6001sg battery,[7] and the autoignition temperature of magnesium ribbon is approximately 473 °C (746 K; 883 °F).[16] It produces intense, bright, white light when it burns. Magnesium's high burning temperature makes it a useful tool for starting emergency fires during outdoor recreation. Other uses include flash photography, flares, pyrotechnics and fireworks sparklersHP Pavilion dv6-6001eg battery.Magnesium firestarter (in left hand), used with a pocket knife and flint to create sparks that ignite the shavingsIn the form of turnings or ribbons, to prepare Grignard reagents, which are useful in organic synthesis.As an additive agent in conventional propellants and the production of nodular graphite in cast ironHP Pavilion dv6-6001ea battery.As a reducing agent for the production of uranium and other metals from their salts.As a sacrificial (galvanic) anode to protect underground tanks, pipelines, buried structures, and water heaters.Alloyed with zinc to produce the zinc sheet used in photoengraving plates in the printing industry, dry-cell battery walls, and roofingHP Pavilion dv6-6000eg battery.[13]As a metal, this element's principal use is as an alloying additive to aluminium with these aluminium-magnesium alloys being used mainly for beverage cans.[edit]In magnesium compoundsMagnesium compounds, primarily magnesium oxide (MgO), are used as refractory a material in furnace linings for producing iron, steel, nonferrous metals, glass and cement( HP Pavilion dv6-3362sf battery) . Magnesium oxide and other magnesium compounds are also used in the agricultural, chemical, and construction industries.Magnesium reacted with an alkyl halide gives a Gringard reagent, which is a very useful tool for preparing alcohols.In agriculture and biology, the magnesium ion is necessary for all life (see magnesium in biology), so magnesium salts are frequently included in various foods, fertilizers (magnesium is a component of chlorophyll), and culture media( HP Pavilion dv6-3362ef battery) .[edit]Niche and illustrative uses of magnesium compounds[edit]BiologicalMagnesium sulfate, as the heptahydrate called Epsom salts, is used as bath salts, as a laxative, and as a highly soluble fertilizer.Magnesium hydroxide, suspended in water, is used in milk of magnesia antacids and laxatives.Magnesium chloride, oxide, gluconate, malate, orotate, glycinate and citrate are all used as oral magnesium supplements( HP Pavilion dv6-3355sf battery) . Oral magnesium supplements have been claimed to be therapeutic for some individuals who suffer from Restless Leg Syndrome (RLS).[citation needed]Magnesium borate, magnesium salicylate, and magnesium sulfate are all used as antiseptics.Magnesium bromide is used as a mild sedative (this action is due to the bromide, not the magnesium) ( HP Pavilion dv6-3355ef battery) .Magnesium stearate is a slightly flammable white powder with lubricating properties. In pharmaceutical technology, it is used in the manufacturing of numerous kinds of tablets to prevent the tablets from sticking to the equipment during the tablet compression process (i.e., when the tablet's substance is pressed into tablet form) ( HP Pavilion dv6-3351sf battery) .Magnesium carbonate powder is used by athletes such as gymnasts, weightlifters and climbers to eliminate moisture and improving the grip on a gymnastic apparatus, lifting bar and climbing rocks.[edit]Non biologicalDead-burned magnesite (magnesium carbonate) is used for refractory purposes such as brick and liners in furnaces and converters.Magnesium sulfite is used in the manufacture of paper (sulfite process).Magnesium phosphate is used to fireproof wood used in construction.Magnesium hexafluorosilicate is used in mothproofing of textiles( HP Pavilion dv6-3351ef battery) .[edit]Biological roleMain article: Magnesium in biologyBecause of the important interaction between phosphate and magnesium ions, magnesium ions are essential to the basic nucleic acid chemistry of life, and thus are essential to all cells of all known living organisms. Over 300 enzymes require the presence of magnesium ions for their catalytic action( HP Pavilion dv6-3350sf battery) , including all enzymes utilizing or synthesizing ATP, or those that use other nucleotides to synthesize DNA and RNA. ATP exists in cells normally as a chelate of ATP and a magnesium ion.Plants have an additional use for magnesium in that chlorophylls are magnesium-centered porphyrins. Magnesium deficiency in plants causes late-season yellowing between leaf veins, especially in older leaves( HP Pavilion dv6-3350ef battery) , and can be corrected by applying Epsom salts (which is rapidly leached), or else crushed dolomitic limestone to the soil.Examples of food sources of magnesiumMagnesium is a vital component of a healthy human diet. Human magnesium deficiency (including conditions that show few overt symptoms) is relatively rare[17] although only 32% of the United States meet the RDA-DRI;[18] low levels of magnesium in the body has been associated with the development of a number of human illnesses such as asthma, diabetes, and osteoporosis( HP Pavilion dv6-3300sg battery) .[19]Adult human bodies contain about 24 grams of magnesium, with 60% in the skeleton, 39% intracellular (20% in skeletal muscle), and 1% extracellular. Serum levels are typically 0.7–1.0 mmol/L or 1.8–2.4 mEq/L. Serum magnesium levels may appear normal even in cases of underlying intracellular deficiency( HP Pavilion dv6-3300 battery) , although no known mechanism maintains a homeostatic level in the blood other than renal excretion of high blood levels.Intracellular magnesium is correlated with intracellular potassium. Magnesium is absorbed in the gastrointestinal tract, with more absorbed when status is lower. In humans, magnesium appears to facilitate calcium absorption[citation needed]. Low and high protein intake inhibit magnesium absorption( HP Pavilion dv6-3299ea battery) , and other factors such as phosphate, phytate, and fat affect absorption. Absorbed dietary magnesium is largely excreted through the urine, although most magnesium "administered orally" is excreted through the feces.[20] Magnesium status may be assessed roughly through serum and erythrocyte Mg concentrations and urinary and fecal excretion( HP Pavilion dv6-3298ea battery) , but intravenous magnesium loading tests are likely the most accurate and practical in most people.[21] In these tests, magnesium is injected intravenously; a retention of 20% or more indicates deficiency.[22] Other nutrient deficiencies are identified through biomarkers, but none are established for magnesium( HP Pavilion dv6-3180ea battery) .[23]Spices, nuts, cereals, coffee, cocoa, tea, and vegetables are rich sources of magnesium. Green leafy vegetables such as spinach are also rich in magnesium as they contain chlorophyll. Observations of reduced dietary magnesium intake in modern Western countries compared to earlier generations may be related to food refining and modern fertilizers that contain no magnesium( HP Pavilion dv6-3163eo battery) .[20]Numerous magnesium dietary supplements are available. Magnesium oxide, one of the most common because it has high magnesium content per weight, has been reported to be the least bioavailable.[24][25] Magnesium citrate has been reported as more bioavailable than oxide or amino-acid chelate (glycinate) forms( HP Pavilion dv6-3150sa battery) .[26]Excess magnesium in the blood is freely filtered at the kidneys, and for this reason it is difficult to overdose on magnesium from dietary sources alone.[19] With supplements, overdose is possible, however, particularly in people with poor renal function; occasionally, with use of high cathartic doses of magnesium salts( HP Pavilion dv6-3141sa battery) , severe hypermagnesemia has been reported to occur even without renal dysfunction.[27] Alcoholism can produce a magnesium deficiency, which is easily reversed by oral or parenteral administration, depending on the degree of deficiency.[28][edit]Detection in biological fluidsMagnesium concentrations in plasma or serum may be measured to monitor for efficacy and safety in those receiving the drug therapeutically, to confirm the diagnosis in potential poisoning victims or to assist in the forensic investigation in a case of fatal overdosage( HP Pavilion dv6-3140sa battery) . The newborn children of mothers who received parenteral magnesium sulfate during labor may exhibit toxicity at serum magnesium levels that were considered appropriate for the mothers.[29][edit]Magnesium in treatment-resistant depression (TRD)There has been some speculation that magnesium deficiency can lead to depression. Cerebral spinal fluid (CSF) magnesium has been found low in treatment-resistant suicidal depression and in patients that have attempted suicide( HP Pavilion dv6-3131sa battery) . Brain magnesium has been found low in TRD using phosphorus nuclear magnetic resonance spectroscopy, an accurate means for measuring brain magnesium. Blood and CSF magnesium do not appear well-correlated with major depression.[30] Magnesium chloride in relatively small doses was found to be as effective in the treatment of depressed elderly type 2 diabetics with hypomagnesemia as imipramine 50 mg daily( HP Pavilion dv6-3130sa battery) .[31][edit]Safety precautions for magnesium metalThe magnesium-bodied Honda RA302 of Jo Schlesser crashes and burns during the 1968 French Grand Prix. Schlesser was killed. The magnesium car body did not cause the fire or the death, but it greatly hindered attempts to douse the fire with water( HP Pavilion dv6-3127sa battery) .[citation needed]Magnesium metal and its alloys are explosive hazards; they are highly flammable in their pure form when molten or in powder or ribbon form. Burning or molten magnesium metal reacts violently with water. When working with powdered magnesium, safety glasses with welding eye protection are employed( HP Pavilion dv6-3125sa battery) , because the bright white light produced by burning magnesium contains ultraviolet light that can permanently damage the retinas of the eyes.[32]Magnesium is capable of reducing water to the highly flammable hydrogen gas:[33]Mg (s) + 2 H2O (l) → Mg(OH)2 (s) + H2 (g)As a result, water cannot be used to extinguish magnesium fires; the hydrogen gas produced will only intensify the fire. Dry sand is an effective smothering agent but is usable only on relatively level and flat surfaces( HP Pavilion dv6-3123sa battery) .Magnesium also reacts with carbon dioxide to form magnesium oxide and carbon:2 Mg (s) + CO2 → 2 MgO (s) + C (s)hence, carbon dioxide fire extinguishers cannot be used for extinguishing magnesium fires either.[34]Burning magnesium is usually quenched by using a Class D dry chemical fire extinguisher, or by covering the fire with sand or magnesium foundry flux to remove its air source.nt growth in pH-neutral soils, the concentration in acid soils of toxic Al3+ cations increases and disturbs root growth and function. ( HP Pavilion dv6-3122sa battery) Most acid soils are saturated with aluminium rather than hydrogen ions. The acidity of the soil is therefore a result of hydrolysis of aluminium compounds.[89] This concept of "corrected lime potential"[90] to define the degree of base saturation in soils became the basis for procedures now used in soil testing laboratories to determine the "lime requirement"[91] of soils. ( HP Pavilion dv6-3121sa battery) Wheat's adaptation to allow aluminium tolerance is such that the aluminium induces a release of organic compounds that bind to the harmful aluminium cations. Sorghum is believed to have the same tolerance mechanism. The first gene for aluminium tolerance has been identified in wheat. It was shown that sorghum's aluminium tolerance is controlled by a single gene, as for wheat.[93] This is not the case in all plants( HP Pavilion dv6-3120sa battery) .Magnesium ( /mæɡˈniːziəm/ mag-nee-zee-əm) is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust [2] and ninth in the known universe as a whole.[3][4] Magnesium is the fourth most common element in the Earth as a whole (behind iron, oxygen and silicon) ( HP Pavilion dv6-3119sa battery) , making up 13% of the planet's mass and a large fraction of the planet's mantle. The relative abundance of magnesium is related to the fact that it is easily built up in supernova stars from a sequential addition of three helium nuclei to carbon (which in turn is made from three helium nuclei). Due to magnesium ion's high solubility in water, it is the third most abundant element dissolved in seawater. ( HP Pavilion dv6-3118sa battery) The free element (metal) is not found naturally on Earth, as it is highly reactive (though once produced, it is coated in a thin layer of oxide [see passivation], which partly masks this reactivity). The free metal burns with a characteristic brilliant white light, making it a useful ingredient in flares. The metal is now mainly obtained by electrolysis of magnesium salts obtained from brine. Commercially( HP Pavilion dv6-3117sa battery) , the chief use for the metal is as an alloying agent to make aluminium-magnesium alloys, sometimes called "magnalium" or "magnelium". Since magnesium is less dense than aluminium, these alloys are prized for their relative lightness and strength.In human biology, magnesium is the eleventh most abundant element by mass in the human body; its ions are essential to all living cells( HP Pavilion dv6-3116tx battery) , where they play a major role in manipulating important biological polyphosphate compounds like ATP, DNA, and RNA. Hundreds of enzymes thus require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives, antacids (e.g., milk of magnesia) ( HP Pavilion dv6-3116sa battery) , and in a number of situations where stabilization of abnormal nerve excitation and blood vessel spasm is required (e.g., to treat eclampsia). Magnesium ions are sour to the taste, and in low concentrations they help to impart a natural tartness to fresh mineral waters.In vegetation magnesium is the metallic ion at the center of chlorophyll, and is thus a common additive to fertilizers( HP Pavilion dv6-3115tx battery) .[6]
Bolivia officially known as Plurinational State of Bolivia (Spanish: Estado Plurinacional de Bolivia, Quechua: Bulivya Mamallaqta, Aymara: Wuliwya Suyu), is a landlocked country in central South America. It is bordered by Brazil to the north and east, Paraguay and Argentina to the south, Chile to the southwest( Dell D6400 battery) , and Peru to the west.Prior to European colonization, the Andean region of Bolivia was a part of the Inca Empire – the largest state in Pre-Columbian America. The Spanish Empire conquered the region in the 16th century. During most of the Spanish colonial period, this territory was called Upper Peru and was under the administration of the Viceroyalty of Peru( Dell HF674 battery) , which included most of Spain's South American colonies. After declaring independence in 1809, 16 years of war followed before the establishment of the Republic, named for Simón Bolívar, on 6 August 1825. Bolivia has struggled through periods of political instability, dictatorships and economic woes( Dell N3010 battery) .Bolivia is a democratic republic that is divided into nine departments. Its geography is varied from the peaks of the Andes in the West, to the Eastern Lowlands, situated within the Amazon Basin. It is a developing country, with a Medium Human Development Index score, and a poverty level of 53%.( Dell Inspiron N4010 battery) Its main economic activities include agriculture, forestry, fishing, mining, and manufacturing goods such as textiles, clothing, refined metals, and refined petroleum. Bolivia is very wealthy in minerals, especially tin.The Bolivian population, estimated at 10 million, is multiethnic, including Amerindians, Mestizos, Europeans, and Africans( Dell INSPIRON 1100 battery) . The main language spoken is Spanish, although the Aymara and Quechua languages are also common and all three, as well as 34 other indigenous languages, are official. The large number of different cultures within Bolivia has contributed greatly to a wide diversity in fields such as art, cuisine, literature, and music( Dell Inspiron 1200 battery) .EtymologyBolivia was named for Simón Bolívar, a leader in the Spanish American wars of independence.[13] Antonio José de Sucre had been given the option by Bolívar to either keep Upper Peru (present-day Bolivia) under the newly formed Republic of Peru, to unite with the United Provinces of Rio de la Plata, or to formally declare its independence from the Viceroyalty of Peru that had dominated most of the region( Dell Inspiron 1420 battery) . Sucre opted to create a new nation and, with local support, named it in honor of Simón Bolívar.[14]However, the original name given to the newly formed country was Republic of Bolívar. The name would not change to Bolivia until some days later when congressman Manuel Martín Cruz proposed: "If from Romulus comes Rome, then from Bolívar comes Bolivia" (Spanish: Si de Rómulo Roma, de Bolívar Bolivia) ( Dell Inspiron 1464 battery) . The name stuck and was approved by the Republic on 3 October 1825.[15]In 2009, a new constitution changed the country's name from the "Republic of Bolivia" to the "Plurinational State of Bolivia" in recognition of the multi-ethnic nature of the country and the enhanced position of Bolivia's indigenous peoples under the new constitution( Dell Inspiron 1564 battery) .[edit]HistoryMain article: History of BoliviaTiwanaku at its largest territorial extent, AD 950The region that is now known as Bolivia has been occupied for over 2,000 years, when the Aymara arrived in the region. Present-day Aymara associate themselves with an advanced civilization situated at Tiwanaku, in Western Bolivia. The capital city of Tiwanaku dates from as early as 1500 BC when it was a small agriculturally based village. ( Dell Inspiron 1764 battery) The community grew to urban proportions between AD 600 and AD 800, becoming an important regional power in the southern Andes. According to early estimates, at its maximum extent, the city covered approximately 6.5 square kilometers, and had between 15,000 – 30,000 inhabitants( Dell Inspiron 1520 battery) .[20] However, satellite imaging was used recently to map the extent of fossilized suka kollus across the three primary valleys of Tiwanaku, arriving at population-carrying capacity estimates of anywhere between 285,000 and 1,482,000 people.[21]Around AD 400, Tiwanaku went from being a locally dominant force to a predatory state. Tiwanaku expanded its reaches into the Yungas and brought its culture and way of life to many other cultures in Peru, Bolivia, and Chile( Dell Inspiron 1521 battery) . However, Tiwanaku was not a violent culture in many respects. In order to expand its reach, Tiwanaku exercised great political astuteness, creating colonies, fostering trade agreements (which made the other cultures rather dependent), and instituting state cults. ( Dell inspiron 1525 battery) The empire continued to grow with no end in sight. William H. Isbell states that "Tiahuanaco underwent a dramatic transformation between AD 600 and 700 that established new monumental standards for civic architecture and greatly increased the resident population." ( Dell inspiron 1526 battery) Tiwanaku continued to absorb cultures rather than eradicate them. Archaeologists note a dramatic adoption of Tiwanaku ceramics into the cultures which became part of the Tiwanaku empire. Tiwanaku's power was further solidified through the trade it implemented among the cities within its empire. ( Dell Inspiron 1720 battery) Tiwanaku's elites gained their status through the surplus food they controlled, collected from outlying regions and then redistributed to the general populace. Further, this elite's control of llama herds became a powerful control mechanism as llamas were essential for carrying goods between the civic centre and the periphery( Dell Inspiron 2000 battery) . These herds also came to symbolize class distinctions between the commoners and the elites. Through this control and manipulation of surplus resources, the elite's power continued to grow until about AD 950. At this time a dramatic shift in climate occurred.( Dell INSPIRON 2600 battery) There occurred a significant drop in precipitation in the Titicaca Basin. Some archaeologists venture to label this a major drought. As the rainfall decreased, many of the cities further away from Lake Titicaca began to tender less foodstuffs to the elites. As the surplus of food decreased, and thus the amount available to underpin their power( Dell INSPIRON 3800 battery) , the control of the elites began to falter. The capital city became the last place viable place for food production due to the resiliency of the raised field method of agriculture. But, in the end, even this more productive design for food production was no match for the vagaries of the weather. Tiwanaku disappeared around AD 1000 because food production( Dell INSPIRON 4000 battery) , the main source of the power elite's control, dried up. The area remained uninhabited for centuries thereafter.[24]Inca Expansion (1438–1527)Between 1438 and 1527, the Inca empire, during its last great expansion, gained control over much of what is now western Bolivia. The Incas would not maintain control of the region for long however, as the rapidly expanding Inca Empire was internally weak. As such, the impending Spanish conquest would be remarkably easy( Dell Inspiron 5000 battery) .[edit]Colonial periodThe Spanish conquest of the Inca empire began in 1524, and was mostly completed by 1533. The territory now called Bolivia was known as "Upper Peru", and was under the authority of the Viceroy of Lima. Local government came from the Audiencia de Charcas located in Chuquisaca (La Plata—modern Sucre) ( Dell INSPIRON 500M battery) . Founded in 1545 as a mining town, Potosí soon produced fabulous wealth, becoming the largest city in the New World with a population exceeding 150,000 people.[25]By the late 16th century Bolivian silver was an important source of revenue for the Spanish Empire.[26] A steady stream of natives served as labor force (the Spanish employed the pre-Columbian draft system called the mita) ( Dell INSPIRON 5100 battery) .[27] Upper Peru was bounded to Viceroyalty of the Río de la Plata in 1776. Túpac Katari led the indigenous rebellion that laid siege to La Paz in March 1781, during which 20,000 people died.[28] As Spanish royal authority weakened during the Napoleonic wars, sentiment against colonial rule grew( Dell INSPIRON 510M battery) .[edit]Independence and subsequent warsThe struggle for independence started in the city of Sucre in 1809, with the Chuquisaca Revolution (Chuquisaca was then the name of the city). That revolution, which created a local government Junta, was followed by the La Paz revolution, during which Bolivia actually declared independence. Both revolutions were short-lived( Dell INSPIRON 6000 battery) , and defeated by the Spanish authorities, but the following year the Spanish American wars of independence raged across the continent. Bolivia was captured and recaptured many times during the war by the royalists and patriots. Buenos Aires sent three military campaigns, all of which were defeated, and eventually limited itself to protecting the national borders at Salta( Dell INSPIRON 600M battery) . Bolivia was finally freed of Royalist dominion by Antonio José de Sucre, with a military campaign coming from the North in support of the campaign of Simón Bolívar. After 16 years of war the Republic was proclaimed on 6 August 1825 and named Bolivia in honor of Bolívar( Dell Inspiron 6400 battery) .In 1836, Bolivia, under the rule of Marshal Andrés de Santa Cruz, invaded Peru to reinstall the deposed president, General Luis José de Orbegoso. Peru and Bolivia formed the Peru-Bolivian Confederation, with de Santa Cruz as the Supreme Protector. Following tension between the Confederation and Chile, Chile declared war on 28 December 1836. Argentina, Chile's ally( Dell INSPIRON 7000 battery) , declared war on the Confederation on 9 May 1837. The Peruvian-Bolivian forces achieved several major victories during the War of the Confederation: the defeat of the Argentine expedition and the defeat of the first Chilean expedition on the fields of Paucarpata near the city of Arequipa( Dell INSPIRON 700M battery) .On the same field, the Chilean and Peruvian rebel army surrendered unconditionally and signed the Paucarpata Treaty. The treaty stipulated that Chile would withdraw from Peru-Bolivia, Chile would return captured Confederate ships, economic relations would be normalized, and the Confederation would pay Peruvian debt to Chile( Dell Inspiron 710m battery) . In Chile, public outrage over the treaty forced the government to reject it. Chile organized a second attack on the Confederation and defeated it in the Battle of Yungay. After this defeat, Santa Cruz resigned and went to exile in Ecuador and then Paris, and the Peruvian-Bolivian Confederation was dissolved( Dell INSPIRON 8200 battery) .Following the independence of Peru, Peruvian president General Agustín Gamarra invaded Bolivia. The Peruvian army was decisively defeated at the Battle of Ingavi on 20 November 1841 where Gamarra was killed. The Bolivian army under General José Ballivián then mounted a counter-offensive, capturing the Peruvian port of Arica( Dell INSPIRON 8600 battery) . Later, both sides signed a peace treaty in 1842, putting a final end to the war.[edit]Economic instability and continued warsA period of political and economic instability in the early-to-mid-19th century weakened Bolivia. Then in the War of the Pacific (1879–83) against Chile, it lost its access to the sea and the adjoining rich salitre (saltpeter) fields, together with the port of Antofagasta( Dell INSPIRON 9100 battery) .Since independence, Bolivia has lost over half of its territory to neighboring countries in wars and as a consequence of internal strife. [29] It also lost the state of Acre, in the Acre War; important because this region was known for its production of rubber. Peasants and the Bolivian army fought briefly but after a few victories( Dell INSPIRON 9200 battery) , and facing the prospect of a total war against Brazil, it was forced to sign the Treaty of Petrópolis in 1903, in which Bolivia lost this rich territory. Popular myth has it that Bolivian president Mariano Melgarejo (1864–71) traded the land for what he called "a magnificent white horse" and Acre was subsequently flooded by Brazilians which ultimately led to confrontation and fear of war with Brazil( Dell INSPIRON 9300 battery) .In the late 19th century, an increase in the world price of gold brought Bolivia relative prosperity and political stability. During the early 20th century, tin replaced gold as the country's most important source of wealth. A succession of governments controlled by the economic and social elite followed laissez-faire capitalist policies through the first thirty years of the 20th century. ( Dell Inspiron 9400 battery) Living conditions of the native people, who constitute most of the population, remained deplorable. With work opportunities limited to primitive conditions in the mines and in large estates having nearly feudal status, they had no access to education, economic opportunity, and political participation. Bolivia's defeat by Paraguay in the Chaco War (1932–35) ( Dell Inspiron E1505 battery) , where Bolivia lost a great part of the Gran Chaco region in dispute, marked a turning-point.[edit]Nationalist Revolutionary MovementA llama in the Laguna Colorada, a shallow salt lake in the southwestern Bolivian sector of the Altiplano.The Revolutionary Nationalist Movement (MNR) The most historic political party, emerged as a broadly based party. Denied its victory in the 1951 presidential elections, the MNR led a successful revolution in 1952( Dell Inspiron E1705 battery) . Under President Víctor Paz Estenssoro, the MNR, having strong popular pressure, introduced universal suffrage into his political platform and carried out a sweeping land-reform promoting rural education and nationalization of the country's largest tin mines.12 years of tumultuous rule left the MNR divided( Dell Inspiron Mini 9 battery) . In 1964, a military junta overthrew President Estenssoro at the outset of his third term. The 1969 death of President René Barrientos Ortuño, a former member of the junta who was elected president in 1966, led to a succession of weak governments. Alarmed by the rising Popular Assembly and the increase in the popularity of President Juan José Torres, the military( Dell Latitude D400 battery) , the MNR, and others installed Colonel (later General) Hugo Banzer Suárez as president in 1971.Coming back to the presidency in 1985-1989; 1993-1997; and 2002-2003[edit]CIA activities and leftist insurgencyFurther information: CIA activities in Bolivia and Ñancahuazú GuerrillaThe CIA had been active in providing finances and training to the Bolivian military in 1960s. The revolutionary leader Che Guevara was killed by a team of CIA officers and members of the Bolivian Army on 9 October 1967, in Bolivia( Dell STUDIO 1450 battery) . The CIA reported that Guevara was captured on 8 October as a result of the clash with the Cuban-led guerrillas. He had a wound in his leg, but was otherwise in fair condition. At 1150 hours on 9 October the Second Ranger Battalion received direct orders from Bolivian Army Headquarters in La Paz to kill Guevara( Dell Vostro 1400 battery) . These orders were carried out at 1315 hours the same day with a burst of fire from an M-2 automatic rifle. Félix Rodríguez was a CIA officer on the team with the Bolivian Army that captured and shot Guevara.[34] Rodriguez said that after he received a Bolivian presidential execution order, he told "the soldier who pulled the trigger to aim carefully( Dell Vostro 1500 battery) , to remain consistent with the Bolivian government's story that Che had been killed in action during a clash with the Bolivian army." Rodriguez said the US government had wanted Che in Panama, and "I could have tried to falsify the command to the troops, and got Che to Panama as the US government said they had wanted", said Mr Rodriguez( Dell XPS M1210 battery) , but he chose to "let history run its course" as desired by Bolivia."[35][edit]Military governments: García Meza and Siles ZuazoElections in 1979 and 1981 were inconclusive and marked by fraud. There were coups d'état, counter-coups, and caretaker governments. In 1980, General Luis García Meza Tejada carried out a ruthless and violent coup d'état that did not have popular support. He pacified the people by promising to remain in power only for one year( Dell XPS M1330 battery) . (At the end of the year, he staged a televised rally to claim popular support and announced, "Bueno, me quedo", or, "All right; I'll stay [in office]."[36] He was deposed shortly thereafter.) His government was notorious for human-rights-abuses, drug-trafficking, and economic mismanagement; during his presidency( Dell XPS 1340 battery) , the inflation that later crippled the Bolivian economy could already be felt. Later convicted in absentia for various crimes by attorney Juan del Granado, including murder, García Meza was extradited from Brazil and began serving a 30-year prison sentence in 1995( Dell XPS M1530 battery) .After a military rebellion forced out Meza in 1981, three other military governments in 14 months struggled with Bolivia's growing problems. Unrest forced the military to convoke the Congress elected in 1980 and allow it to choose a new chief executive. In October 1982, Hernán Siles Zuazo again became president, 22 years after the end of his first term of office (1956–60) ( Dell XPS M170 battery) .[edit]Sánchez de Lozada and Banzer: Liberalizing the economyGonzalo Sánchez de Lozada pursued an aggressive economic and social reform agenda. The most dramatic reform was the "capitalization" program, under which investors, typically foreign, acquired 50% ownership and management control of public enterprises, such as the state petroleum corporation, telecommunications system( Dell XPS M1710 battery) , airlines, railroads, and electric utilities, in return for agreed upon capital investments.Gonzalo Sánchez de LozadaThe reforms and economic restructuring were strongly opposed by certain segments of society, which instigated frequent and sometimes violent protests, particularly in La Paz and the Chapare coca-growing region, from 1994 through 1996( Dell XPS M1730 battery) . The de Lozada government pursued a policy of offering monetary compensation for voluntary eradication of illegal coca by its growers in the Chapare region. The policy produced little net reduction in coca, and in the mid-1990s Bolivia accounted for about one-third of the world's coca that was being processed into cocaine( Dell XPS M2010 battery) . The coca leaf has long been part of the Bolivian culture, as indigenous workers have traditionally used the leaf for its properties as a mild stimulant and appetite suppressant.During this time, the umbrella labor-organization of Bolivia, the Central Obrera Boliviana (COB), became increasingly unable to effectively challenge government policy. A teachers' strike in 1995 was defeated because the COB could not marshal the support of many of its members( Dell Latitude E5400 battery) , including construction and factory workers. The state also used selective martial law to keep the disruptions caused by the teachers to a minimum. The teachers were led by Trotskyites, and were considered to be the most militant union in the COB. Their downfall was a major blow to the COB, which also became mired in internal corruption and infighting in 1996( Dell Latitude E5500 battery) .In the 1997 elections, General Hugo Banzer, leader of the Nationalist Democratic Action party (ADN) and former dictator (1971–78), won 22% of the vote, while the MNR candidate won 18%. General Banzer formed a coalition of the ADN, MIR, UCS, and CONDEPA parties, which held a majority of seats in the Bolivian Congress( Dell Latitude E6400 battery) . The Congress elected him as president, and he was inaugurated on 6 August 1997. During the election campaign, Banzer had promised to suspend the privatization of the state-owned oil-company, YPFB. But this seemed unlikely to happen, considering Bolivia's weak position globally. The Banzer government basically continued the free-market and privatization-policies of its predecessor( Dell Latitude E6500 battery) .The relatively robust economic growth of the mid-1990s continued until about the third year of its term in office. After that, regional, global and domestic factors contributed to a decline in economic growth. Financial crises in Argentina and Brazil, lower world prices for export commodities, and reduced employment in the coca sector depressed the Bolivian economy( Dell Inspiron Mini 12 battery) . The public also perceived a significant amount of public sector corruption. These factors contributed to increasing social protests during the second half of Banzer's term.[37]At the outset of his government, President Banzer launched a policy of using special police-units to physically eradicate the illegal coca of the Chapare region. The policy produced a sudden and dramatic four-year decline in Bolivia's illegal coca crop, to the point that Bolivia became a relatively small supplier of coca for cocaine( Dell XPS M140 battery) . Those left unemployed by coca eradication streamed into the cities, especially El Alto, the slum-neighborhood of La Paz. The MIR of Jaime Paz Zamora remained a coalition-partner throughout the Banzer government, supporting this policy (called the Dignity Plan). ( Dell XPS 13 battery) Between January 1999 and April 2000, large-scale protests erupted in Cochabamba, Bolivia's third largest city, in response to the privatization of water resources by foreign companies and a subsequent doubling of water prices.On 6 August 2001, Banzer resigned from office after being diagnosed with cancer. He died less than a year later. Vice President Jorge Fernando Quiroga Ramírez completed the final year of his term( Dell XPS 16 battery) .In the June 2002 national elections, former President Gonzalo Sánchez de Lozada (MNR) placed first with 22.5% of the vote, followed by coca-advocate and native peasant-leader Evo Morales (Movement Toward Socialism, MAS) with 20.9%. Morales edged out populist candidate Manfred Reyes Villa of the New Republican Force( Dell XPS 1640 battery) (NFR) by just 700 votes nationwide, earning a spot in the congressional run-off against Sánchez de Lozada on 4 August 2002.A July agreement between the MNR and the fourth-place MIR, which had again been led in the election by former President Jaime Paz Zamora, virtually ensured the election of Sánchez de Lozada in the congressional run-off( Dell XPS 1645 battery) , and on 6 August he was sworn in for the second time. The MNR platform featured three overarching objectives: economic reactivation (and job creation), anti-corruption, and social inclusion.La Paz skyline. The city is the highest capital in the world.In 2003 the Bolivian gas conflict broke out. On 12 October 2003 the government imposed martial law in El Alto after 16 people were shot by the police and several dozen wounded in violent clashes which erupted when a caravan of oil trucks escorted by police and soldiers deploying tanks and heavy-caliber machine guns tried to breach a barricade( Dell XPS 1647 battery) . On 17 October 2003 Evo Morales' supporters from Cochabamba tried to march into Santa Cruz de la Sierra, the largest city of the eastern lowlands where support was strong for the president. They were turned back. Faced with the option of resigning or more bloodshed, Sanchez de Lozada offered his resignation in a letter to an emergency session of Congress( Dell Latitude 131L battery) . After his resignation was accepted and his vice president, Carlos Mesa, invested, he left on a commercially scheduled flight for the United States.In March 2004, the new president Carlos Mesa announced that his government would hold a series of rallies around the country, and at its embassies abroad, demanding that Chile return to Bolivia a stretch of seacoast that the country lost in 1884 after the end of the War of the Pacific. Chile has traditionally refused to negotiate on the issue( Dell Latitude C400 battery) , but Mesa nonetheless made this policy a central point of his administration.However, the country's internal situation became unfavorable for such political action on the international stage. After a resurgence of gas protests in 2005, Carlos Mesa attempted to resign in January 2005, but his offer was refused by Congress. On 22 March 2005( Dell Latitude C500 battery) , after weeks of new street protests from organizations accusing Mesa of bowing to U.S. corporate interests, Mesa again offered his resignation to Congress, which was accepted on 10 June. The chief justice of the Supreme Court, Eduardo Rodríguez, was sworn as interim president to succeed the outgoing Carlos Mesa( Dell Latitude C510 battery) .[edit]Plan de TodosMobilizing against neoliberalism as a common enemy of the people, the indigenous population of the Andean region was able to achieve widespread government reform.[39] Bolivia, in particular, was quite successful due to the prominence of an indigenous population and the persistence of reformist policies( Dell Latitude C540 battery) . In 1993, Gonzalo Sanchez de Lozada ran for president in alliance with the Tupac Katari Revolutionary Liberation Movement, which inspired indigenous-sensitive and multicultural-aware policies.[40] Gonzalo Sanchez de Lozada (colloquially known as Goni) was able to shift Bolivian society by selling state firms and constitutionally acknowledging the existence of a multicultural and multiethnic population( Dell Latitude C600 battery) . Current development has led to a neoliberal citizenship regime in which civil rights are expressed through private property ownership, formal democracy and representation, and an investment in the maintaining of infrastructure.In the 1990s, Bolivia introduced, the Plan de Todos, which led to the decentralization of government( Dell Latitude C610 battery) , introduction of intercultural bilingual education, implementation of agrarian legislation, and privatization of state owned businesses. The Plan de Todos main incentive was to encourage popular participation among the Bolivian people. The law recognizes the existence of barrios and rural communities as Territorially Based Organizations (TBOs) and has oversight boards known as rómiles de agilancia( Dell Latitude C640 battery) , or vigilance committees, that are responsible for overseeing municipal governments and planning projects. The Plan formally acknowledged the existence of 311 municipalities, which benefited directly based on the size of their populations. The Plan de Todos inspired the development of a market democracy with minimally regulated capitalist economy( Dell Latitude C800 battery) . The Plan explicitly stated that Bolivian citizens would own a minimum of 51% of enterprises; under the Plan, most state owned enterprises (SOEs), besides mines, were sold.[41] This privatization of SOEs led to innovative neoliberal structuring that acknowledged a diverse population within Bolivia. ( Dell Latitude C810 battery) The Law of Popular Participation[43] gave municipalities the responsibility of maintaining various infrastructures (and offering services): health, education, systems of irrigation, which stripped the responsibility away from the state. The state provides municipalities with twenty percent of federal tax revenue so that each municipality can adequately maintain these infrastructures( Dell Latitude C840 battery) . The Law also redistributes political power to the local level.[edit]The Plurinational State of BoliviaMain article: Presidency of Evo MoralesEvo Morales' inauguration as PresidentThe two main candidates for the 2005 Bolivian presidential election held on 18 December 2005 were Juan Evo Morales Ayma of the MAS Party and Jorge Quiroga, leader of the Social and Democratic Power (PODEMOS) Party and former head of the Acción Democrática Nacionalista (ADN) Party( Dell Latitude CPI battery) . Morales won the election with 53.7% of the votes, an absolute majority, unusual in Bolivian elections. He was sworn in on 22 January 2006, for a five-year term. Prior to his official inauguration in La Paz, he was inaugurated in an Aymara ritual at the archeological site of Tiwanaku before a crowd of thousands of Aymara people and representatives of leftist movements from across Latin America( Dell Latitude CPX battery) . Though highly symbolic, this ritual was not historically based and primarily represented native Aymaras — not the main Quechua-speaking population. Since the Spanish conquest in the early 16th century, this region of South America, where there is a majority native population, has been ruled mostly by descendants of European immigrants( Dell Latitude D410 battery) .On 1 May 2006, Morales caused controversy when he announced his intent to re-nationalize Bolivian hydrocarbon assets. While stating that the initiative would not be an expropriation, Morales sent Bolivian troops to occupy 56 gas installations simultaneously, including the two Petrobras-owned refineries which provide over 90% of Bolivia's refining-capacity( Dell Latitude D420 battery) . All foreign energy firms were required to sign new contracts within 180 days giving Bolivia majority ownership, and up to 82% of revenues for the largest natural gas fields. All such firms signed contracts. Reports from the Bolivian government and the companies involved are contradictory as to plans for future investment. ( Dell Latitude D430 battery) By far the biggest customer for Bolivian hydrocarbons has been Brazil, which imports two-thirds of Bolivia's natural gas via pipelines operated by the semi-private Petrobras. Since gas can only be exported from landlocked Bolivia via Petrobras' large (and expensive) pipelines, the supplier and customer are strongly linked( Dell Latitude D500 battery) . Petrobras has announced plans to produce enough natural gas by 2011 to replace that now supplied by Bolivia. Bolivia's position is strengthened by the knowledge that hydrocarbon reserves are more highly valued now than at the times of previous nationalizations, and by the pledged support of fellow leftist, President Hugo Chávez of Venezuela( Dell Latitude D505 battery) .Fulfilling a campaign promise, Morales opened on 6 August 2006, the Bolivian Constituent Assembly to begin writing a new constitution aimed at giving more power to the indigenous majority.[44] Problems immediately arose when, unable to garner the two-thirds majority needed to include controversial provisions in the constitutional draft( Dell Latitude D510 battery) , Morales' party announced that only a simple majority would be needed to draft individual articles while two-thirds majority would be needed to pass the document in full. Violent protests arose in December 2006 in parts of the country for both two-thirds and departmental autonomy, mostly in the eastern third of the country, where much of the hydrocarbon wealth is located( Dell Latitude D520 battery) . MAS and its supports believed two-thirds voting rules would give an effective veto for all constitutional changes to the conservative minority.In August 2007, more conflicts arose in Sucre, as the city demanded the discussion of the seat of government inside the assembly, hoping the executive and legislative branches could return to the city, but assembly and the government said this demand was overwhelmingly impractical and politically undesirable( Dell Latitude D600 battery) . The conflict turned into violence, and the assembly was moved to a military area in Oruro. Although the main opposition party boycotted the session, a constitutional draft was approved on 24 November.In May 2008, Evo Morales was a signatory to the UNASUR Constitutive Treaty of the Union of South American Nations. Bolivia has ratified the treaty( Dell Latitude D610 battery) .In the 2009 national general elections, Evo Morales was re-elected with 64.22% of the vote. His party, Movement for Socialism, also won a two-thirds majority in both houses of the National Congress.[edit]Administrative divisionsMain articles: Departments of Bolivia, Provinces of Bolivia, Municipalities of Bolivia, Cantons of Bolivia, and Native Community Lands( Dell Latitude D620 battery) Bolivia is divided into nine departments, further subdivided into 112 provinces and these ones into 339 municipalities and into native community lands.[45]According to what is established by the Bolivian Political Constitution, the Law of Autonomies and Decentralization regulates de procedure for the elaboration of Statutes of Autonomy, the transfer and distribution of direct competences between the central government and the autonomous entities( Dell Latitude D630 battery) .[46] There are four levels of decentralization:Departmental GovernmentConstituted by the Departmental Assembly, with rights over the legislation of the department. The governor is chosen by universal suffrage.Municipal GovernmentConstituted by a Municipal Council, with rights over the legislation of the municipality. The mayor is chosen by universal suffrage.Regional GovernmentConformed by several provinces or municipalities of geographical continuity within a department. It is constituted by a Regional Assembly( Dell Latitude D800 battery) .Original Indigenous GovernmentSelf-governance of original indigenous people on the ancient territories where they live.Territorial limitsBolivia's limits on the north and east are with the Federative Republic of Brazil, on the east and southeast with the Republic of Paraguay, on the south with the Argentine Republic, on the southwest with the Republic of Chile and on the west with the Republic of Peru. The total perimeter of the boundaries is 6.834 kilometers( Dell Latitude D810 battery) .Limits with Argentina: This international limit starts at the Zapalari mountain and ends in Esmeralda, Tarija Department (which is a triple boundary point between Bolivia, Argentina and Paraguay). The main boundary points are the Panizo mountain, the Malpaso mountain, the towns of Villazón, Bermejo, Fortín Campero, Yacuiba and Fortín D'Orbigny over the Pilcomayo River( Dell Latitude D820 battery) .Limits with Brazil: This international limit is the most extensive. It starts in the town of Bolbepra and ends on Bahía Negra ("Black Bay"), which is a triple boundary between Brazil, Paraguay and Bolivia. The main boundary points are Brasiléia, located in front of Cobija), the towns of Fortín Manoa (close to the Madeira River) ( Dell Latitude D830 battery) , Villa Bella, Cerro Cuatro Hermanos, San Matías, the La Gaiba Lake, the Mandioré Lake, the Cáceres Lake and the Gutiérrez Guerra Port in the Paraguay River.Limits with Chile: The current limit between Bolivia and Chile was agreed with the Treaty of Peace and Friendship of 1904. This document allowed the surrender of the Bolivian littoral zone and coasts in the Pacific Ocean( Dell Latitude 2100 battery) , making Bolivia a landlocked country. The limits start at Visviri (the boundary point for Bolivia, Chile and Peru) and ends at the Zapaleri mountain, which is a triple boundary point for Chile, Bolivia and Argentina. The main points of the boundary are the Licancabur and Ollagüe volcanos and the Payachata mountains( Dell Latitude 2110 battery) .Limits with Paraguay: It starts in Esmeralda and ends on Bahía Negra, on the Black River. The main boundary points are the Ustares mountain, Palmar de las Islas, Hito Chovoreca and the Jara mountain.Limits with Peru: The boundary starts at the town of Bolbepra (the triple boundary point for Bolivia, Peru and Brazil) and ends on Choquecota and Visviri( Dell Latitude E4300 battery) . The most important points in the international boundary are the Heath Port on the Madre de Dios River, the Apolobamba mountain range and Puerto Acosta, where the division of the Titicaca Lake starts.[edit]Maritime claims and rightsDespite losing its maritime coast, the so-called Littoral Department, after the War of the Pacific, Bolivia has historically maintained, as a state policy, a maritime claim to Chile; the claim asks for sovereign access to the Pacific Ocean and its maritime space( Dell Vostro 1310 battery) . The Political Constitution of 2009 established that Bolivia declares its right to access to the sea, and that its objective is to solve the problem peacefully.Since the foundation of the United Nations in 1945, Bolivia has requested the General Assembly to consider its petition for sovereign access to the Pacific Ocean. The issue has also been presented before the Organization of American States( Dell Vostro 1320 battery) ; in 1979, the OAS passed the 426 Resolution,[48] which declared that the Bolivian problem is a hemispheric problem. Chile has tried to assist in the matter, but without yielding any of its sovereign territory.Access to the Pacific Ocean by Chile. On April 4, 1884, a truce was signed with Chile, whereby Chile gave facilities of access to Bolivian products through Antofagasta( Dell Vostro 1510 battery) , and freed the payment of export rights in the port of Arica. In October 1904, the Treaty of Peace and Friendship was signed, and Chile agreed to build a railway between Arica and La Paz, to improve access of Bolivian products to the ports.Access to the Pacific Ocean by Peru. The Special Economical Zone for Bolivia in Ilo (ZEEBI) is a special economic area of 5 km of maritime coast, and a total extension of 358 hectares( Dell Vostro 1520 battery) , called Mar Bolivia ("Sea Bolivia"), where Bolivia may maintain a free port near Ilo, Peru under its administration and operation[49] for a period of 99 years starting on 1992; once the time has passed, all the construction and territory go back to the Peruvian government.Access to the Atlantic Ocean by Argentina. Since 1964, Bolivia has had its own port facilities in the Bolivian Free Port in Rosario( Dell Vostro 2510 battery) , Argentina. This port is located on the Paraná River, which is directly connected to the Atlantic Ocean.[edit]GeographyMain article: Geography of BoliviaSatellital image of BoliviaBolivia is located in the central zone of South America, between the meridians 57° 26´ and 69° 38´ longitude west of the Prime Meridian, and the parallels 9° 38´ and 22° 53´ of southern latitude. At 1,098,580 square kilometres (424,160 sq mi), Bolivia is the world's 28th-largest country. ( Dell Vostro 1014 battery) Its surface extends from the Central Andes, going partially through the Gran Chaco, as far as the Amazon. The geographic center of the country is the so-called Puerto Estrella ("Star Port") on the Río Grande, in Ñuflo de Chávez Province, Santa Cruz Department.The geographic location of the country comprises a great variety of terrains and climates. Bolivia has a huge degree of biodiversity( Dell Inspiron 1410 battery) , considered one of the greatest in the world; as well as several ecoregions with such ecological subunits as the Altiplano, tropical rainforests (including Amazon rainforest), dry valleys, and the Chiquitania, which is a tropical savanna. All of these feature enormous variations in altitude, from an elevation of 6.542 meters above sea level in Nevado Sajama, to nearly 70 meters along the Paraguay River( Dell Vostro 1014N battery) . Despite this great geographic contrast, Bolivia has remained a landlocked country since the War of the Pacific.[edit]Land reliefContrast of the land relief forms of Bolivia, from an elevation of 4.000 meters in the Andean region (altiplano) to 2.500 meters in the Sub-Andean region (valleys) and to 400 meters in Los Llanos region (savanna) ( Dell Vostro 1015 battery) .Bolivia can be divided into three physiographic regions:Andean Region: in the southwest; it spans 28% of the national territory, extending over 307.603 km². This area is located above 3000 meters altitude, and is located between two big Andean chains: the Cordillera Occidental ("western range") and the Cordillera Central ("central range"), with some of the highest spots in the Americas( Dell Vostro 1015N battery) , such as the Nevado Sajama, with 6,542 meters, and the Illimani with 6,462 meters. Here also is located Lake Titicaca, the highest commercially navigable lake in the world,[51] and also the largest lake in South America,[52][53] shared with Peru. Also in this region is the Altiplano and the Salar de Uyuni, which is the largest salt flat of the world and an important source of lithium( Dell Inspiron 1088 battery) .Sub-Andean region: in the center and south; an intermediate region between the Altiplano and the eastern llanos, it comprises 13% of the territory, extending over 142.815 km². It encompasses the Bolivian valleys and the Yungas region. It is distinguished by its farming activities and its temperate climate( Dell Inspiron 1088N battery) .Llanos region: in the northeast; it comprises 59% of the territory with 648.163 km². It is located to the north of the Cordillera Central; it extends from the Andean foothills to the Paraguay River. It is a region of flatland and small plateaus, all covered by extensive rainforests with enormous biodiversity. The region is located below 400 meters above sea level( Dell Vostro A840 battery) .[edit]HydrographyBolivia has three drainage basins that flow into the Atlantic Ocean or the Pacific Ocean.Amazon Basin, also called the North Basin (724.000 km² / 66% of the territory). The rivers of this basin generally have big meanders, thereby forming lakes such as the Murillo Lake in Pando Department. The main Bolivian tributary to the Amazon basin is the Mamoré River( Dell Vostro A860 battery) , with a length of 2000 km running north to the confluence with the Beni River, 1,113 km of length and the second most important river of the country. The Beni River, along with the Madeira River, forms the main tributary of the Amazon River. From east to west, the basin is formed by other important rivers such as the Madre de Dios River, Orthon River, Abuna River, Yata River and the Guaporé River( Dell Inspiron Mini 1012 battery) . The most important lakes are the Rogaguado Lake and the Rogagua Lake.Rio de la Plata Basin, also called the South Basin (229.500 km² / 21% of the territory). The tributaries are in general less abundant than the ones forming the Amazon basin. It is mainly formed by the Paraguay River, Pilcomayo River and Bermejo River. The most important lakes are the Uberaba Lake and the Mandioré Lake, both located in the Bolivian marshland( SONY PCG-5G2L battery) .The Central Basin, which is an endorrheic basin (145.081 km² / 13% of the territory). The Altiplano has large amounts of lakes and rivers that do not run into any ocean, as they are enclosed by the Andean mountains. The most important river is the Desaguadero River, with a length of 436 km, the longest river of the Altiplano( SONY PCG-5G3L battery) ; it begins in Lake Titicaca and then runs in a southeast direction to the Poopó Lake. The basin is then formed by the Lake Titicaca, Lake Poopó, the Desaguadero River and great salt flats as the Salar de Uyuni and the Coipasa Lake.ClimateThe climate of Bolivia varies drastically from one ecoregion to the other, from the tropics in the eastern llanos to polar climates in the western Andes. The summers are warm, humid in the east and dry in the west( SONY PCG-F305 battery) , with rains that often modify temperatures, humidity, winds, atmospheric pressure and evaporation, giving place to very different climates. When the climatological phenomenon known asEl Niño[54][55] takes place, it provokes great alterations in the weather. Winters are very cold in the west, and it snows around the mountain ranges( SONY PCG-5J1L battery) , while in the western regions, windy days are more usual. The autumn is dry in the non-tropical regions.Llanos. A humid tropical climate with an average temperature of 30°C. The wind coming from the Amazon rainforest causes significant rainfall. Starting in May, there is low precipitation because of dry winds, and most days have clear skies. Even so, winds from the south, called surazos, can bring cooler temperatures lasting several days( SONY PCG-5J2L battery) .Altiplano. Desert-Polar climates, with strong and cold winds. The average temperature ranges from 15 to 20°C. At night, temperatures descend drastically to slightly above 0°C, while during the day, the weather is dry and solar radiation is high. Ground frosts occur every month, and snow is frequent( SONY PCG-5K2L battery) .Valleys and Yungas. Temperate climate. The humid northeastern winds are pushed to the mountains, making this region very humid and rainy. Temperatures are cooler at higher elevations. Snow occurs at altitudes of 2000 meters.Chaco. Subtropical Semi-arid climate. Rain and humidity in January and the rest of the year, with warm days and cool nights( SONY PCG-5L1L battery) .BiodiversityBolivia is part of the "Like-Minded Megadiverse Countries",[56] and has an enormous variety of organisms and ecosystems.Bolivia's variable altitudes, ranging from 90 to 6,542 meters above sea level, allow for a vast biologic diversity. The territory of Bolivia comprises 4 types of biomes, 32 ecological regions, and 199 ecosystems( SONY PCG-6S2L battery) . Within this geographic area there are several natural parks and reserves, such as the Noel Kempff Mercado National Park, the Madidi National Park, the Tunari National Park, the Eduardo Avaroa Andean Fauna National Reserve, and the Kaa-Iya del Gran Chaco National Park and Integrated Management Natural Area, among others( SONY PCG-6S3L battery) .The biodiversity of species may be divided into:Plants: Bolivia boasts over 200,000 species of seeds, including over 1,200 species of fern, 1,500 species of marchantiophyta and moss, and at least 800 species of fungus. In addition, there are more than 3,000 species of medicinal plants. Bolivia is considered the place of origin for such species as peppers and chilli peppers( SONY PCG-6V1L battery) , the peanut, the common bean, the yucca, and several species of palm. Bolivia also naturally produces over 4,000 kinds of potato.Vertebrates: Bolivia has more than 2,900 species, including 398 mammals, over 1,400 birds (70% of birds known in the world, being the sixth most diverse country [57]), 204 amphibians, 277 reptiles, and 635 fresh water fish (as Bolivia is a landlocked country) ( SONY PCG-6W1L battery) . In addition, there are more than 3,000 types of butterfly, and more than 60 domestic animals.GeologyMain article: Geology of BoliviaThe geology of Bolivia comprises a variety of different lithologies as well as tectonic and sedimentary environments. On a synoptic scale, geological units coincide with topographical units. Most elementally, the country is divided into a mountainous western area affected by the subduction processes in the Pacific and an eastern lowlands of stable platforms and shields( SONY PCG-7111L battery) .The Central Bank of BoliviaCochabamba[edit]EconomyMain article: Economy of BoliviaBolivia is one of the poorest and least developed countries in Latin America, despite being rich in natural resources. Bolivia's 2002 gross domestic product (GDP) totaled USD $7.9 billion. Economic growth was about 2.5% per year, and inflation was between 3% and 4% in 2002 (it was under 2% in 2001) ( SONY PCG-71511M battery) . Bolivia was rated 'Repressed' by the 2010 Index of Economic Freedom.[58] However, despite a series of mostly political setbacks, between 2006 and 2009 the Morales administration has spurred growth higher than at any point in the preceding 30 years. The growth was accompanied by a moderate decrease in inequality. ( SONY PCG-6W3L battery) Bolivia's current economic situation remains lackluster, a factor that can be linked to several factors from the past three decades. The first major blow to the Bolivian economy came with a dramatic fall in the price of tin during the early 1980s, which impacted one of Bolivia's main sources of income and one of its major mining-industries. ( SONY PCG-7113L battery) The second major economic blow came at the end of the Cold War in the late 1980s and early 1990s as economic aid was withdrawn by western countries who had previously tried to keep a market-liberal regime in power through financial support.Since 1985, the government of Bolivia has implemented a far-reaching program of macroeconomic stabilization and structural reform aimed at maintaining price stability, creating conditions for sustained growth( SONY PCG-7133L battery) , and alleviating scarcity. A major reform of the customs service in recent years has significantly improved transparency in this area. Parallel legislative reforms have locked into place market-liberal policies, especially in the hydrocarbon and telecommunication sectors, that have encouraged private investment. Foreign investors are accorded national treatment( SONY PCG-7Z1L battery) , and foreign ownership of companies enjoys virtually no restrictions in Bolivia.[61]Bolivia has the second largest natural gas reserves in South America.[62] The government has a long-term sales-agreement to sell natural gas to Brazil through 2019. The government held a binding referendum in 2005 on the Hydrocarbon Law( SONY PCG-7Z2L battery) .The US Geological Service estimates that Bolivia has 5.4 million cubic tonnes of lithium which represents 50%–70% of world reserves. The light metal is used to make high-capacity batteries used in electric cars and such. The spinoff effect of lithium mining could cause Bolivia to become the "Saudi Arabia of the Green World." ( SONY PCG-8Y1L battery) However, to mine for it would involve disturbing the country's salt flats (called Salar de Uyuni), an important natural feature which boosts tourism in the region. The government does not want to destroy this unique natural landscape, to meet the rising world demand for lithium.[63]A Uro woman on a floating islet on Lake Titicaca( SONY PCG-8Y2L battery) In April 2000, Hugo Banzer, the former President of Bolivia, signed a contract with Aguas del Tunari, a private consortium, to operate and improve the water supply in Bolivia's third-largest city, Cochabamba. Shortly thereafter, the company tripled the water rates in that city, an action which resulted in protests and rioting among those who could no longer afford clean water.( SONY PCG-8Z2L battery) Amidst Bolivia's nationwide economic collapse and growing national unrest over the state of the economy, the Bolivian government was forced to withdraw the water contract.Bolivian commercial exports were $1.3 billion in 2002, from a low of $652 million in 1991. Imports were $1.7 billion in 2002. Bolivian tariffs are a uniformly low 10%, with capital equipment charged only 5%. Bolivia's trade-deficit was $460 million in 2002( SONY PCG-8Z1L battery) .Bolivia's trade with neighboring countries is growing, in part because of several regional preferential trade agreements it has negotiated. Bolivia is a member of the Andean Community of Nations and enjoys nominally free trade with other member countries( SONY PCG-7112L battery) .The United States remains Bolivia's largest trading partner (excepting natural resources, such as natural gas). In 2002, the United States exported $283 million of merchandise to Bolivia and imported $162 million.Agriculture accounts for roughly 15% of Bolivia's GDP. Soybeans are the major cash crop, sold into the Andean Community market. Bolivian coca growing is both economically and political important( SONY PCG-6W2L battery) .Bolivia's government remains heavily dependent on foreign assistance to finance development projects. At the end of 2002, the government owed $4.5 billion to its foreign creditors, with $1.6 billion of this amount owed to other governments and most of the balance owed to multilateral development banks( SONY PCG-5K1L battery) . Most payments to other governments have been rescheduled on several occasions since 1987 through the Paris Club mechanism. External creditors have been willing to do this because the Bolivian government has generally achieved the monetary and fiscal targets set by IMF programs since 1987, though economic crises in recent years have undercut Bolivia's normally good record( SONY PCGA-BP2E battery) .The rescheduling of agreements granted by the Paris Club has allowed the individual creditor countries to apply very soft terms to the rescheduled debt. As a result, some countries have forgiven substantial amounts of Bolivia's bilateral debt. The U.S. government reached an agreement at the Paris Club meeting in December 1995 that reduced by 67% Bolivia's existing debt stock( SONY VGP-BPL2 battery) . The Bolivian government continues to pay its debts to the multilateral development banks on time. Bolivia is a beneficiary of the Heavily Indebted Poor Countries (HIPC) and Enhanced HIPC debt relief programs, which by agreement restricts Bolivia's access to new soft loans.The income from tourism becomes increasingly important. Bolivia's tourist industry has grown gradually since about 1990( SONY VGP-BPL4 battery) .People in La Paz city centreFestival in SucreYoung miners at work in Potosí[edit]DemographicsMain article: Demographics of BoliviaBolivia's ethnic distribution is estimated to be 30% Quechua-speaking and 25% Aymara-speaking. The largest of the approximately three dozen native groups are the Quechuas (2.5 million), Aymaras (2 million), then Chiquitano (180,000), and Guaraní (125,000). So the full Amerindian population is at 55%; the remaining 30% is mestizo (mixed Amerindian and white), and around 15% are white. ( SONY VGP-BPL5A battery) The white population consists mostly of criollos, which in turn consist of families of relatively unmixed Spanish ancestry, descended from the early Spanish colonists. These have formed much of the aristocracy since independence. Other smaller groups within the white population are Germans( SONY VGP-BPS2 battery) , who founded the former national airline Lloyd Aéreo Boliviano, as well as Italians, Basques, Croats, Russians, Poles and other minorities, many of whose members descend from families that have lived in Bolivia for several generations. Some 40,000 German-speaking Mennonites live in eastern Bolivia. ( SONY VGP-BPS3 battery) The Afro Bolivian community numbers more than 0.5% of the population, descended from African slaves that were transported to work in Brazil and then migrated westward into Bolivia. They are mostly concentrated in the Yungas region (Nor Yungas and Sud Yungas provinces) in the department of La Paz( SONY VGP-BPS4 battery) . There are also Japanese who are concentrated mostly in Santa Cruz de la Sierra, and Middle Easterners who became prosperous in commerce.Bolivia is one of the least developed countries in South America. Almost two-thirds of its people, many of whom are subsistence farmers, live in poverty. Population density ranges from less than one person per square kilometre in the southeastern plains to about ten per square kilometre (25 per sq. mi) in the central highlands( SONY VGP-BPS5 battery) . As of 2006, the population is increasing about 1.45% per year.[68]Major cities are La Paz (administrative capital), Sucre (constitutional capital), Santa Cruz de la Sierra (largest population), El Alto, Oruro and Cochabamba.HealthMain article: Health in BoliviaIn 2006, life expectancy at birth was 64 for males and 67 for females.[10] A study by UN Development Programme and UNICEF reported that over 230 babies in Bolivia died per day through lack of proper care. The majority of the population has no health insurance.[70] A significant part of the population has no access to healthcare( SONY VGP-BPS5A battery) .[70] Demographic and Health Surveys has completed five surveys in Bolivia since 1989 on a wide range of topics.[71][edit]ReligionMain article: Religion in BoliviaAymara woman prayingCristo de la Concordia in Cochabamba, a symbol of Catholic influence in BoliviaAlthough the great majority of Bolivians are Roman Catholic, Protestant denominations and traditional ethnic Inca religion[72][73] are expanding rapidly.[68] According to a 2001 survey conducted by the National Statistical Institute( SONY VGP-BPS8 battery) , 78% of the population is Roman Catholic, 16% is Protestant and 3% follow other Christian denominations.[74] According to adherents.com, 3.25% of Bolivians follow the Bahá'í Faith which is the largest proportion of any country on a continental mainland.[75] Islam is practiced by the descendants of Arabs and local converts( SONY VGP-BPS8A battery) , constituting a small minority of just over 2000 adherents. There is also a small Jewish community that is almost all Ashkenazim in origin. The state has no official religion.There are colonies of Mennonites in the Santa Cruz Department.[76] Many Native communities interweave pre-Columbia and Christian symbols in their worship( SONY VGP-BPL8 battery) .[edit]LanguageMain article: Languages of BoliviaSpanish 60.7% (official), Quechua 21.2% (official), Aymara 14.6% (official) and additionally 34 languages are official languages. Foreign languages 2.4%, other 1.2% (2001 census according to CIA Factbook). According to Instituto Nacional de Estadística de Bolivia 28.1% of the population of Bolivia spoke an indigenous language as a first language in 2007( SONY VGP-BPS9 battery) . This had increased to 29.4% in 2008. Approximately 90% of the children attend primary-school but often for a year or less. Until the 2001 census the literacy rate was low in many rural areas, but, according to the CIA, the literacy rate was 87% nationwide, which is similar to Brazil's but below the South American average. Nevertheless in 2008 after the campaign "Yes I can"( SONY VGP-BPS9/S battery) , Bolivia was declared illiteracy-free under the UNESCO standards.[77][edit]Politics and governmentMain articles: Politics of Bolivia and Foreign relations of BoliviaThe government building of the National Congress of Bolivia at the Plaza Murillo in central La Paz.Bolivia has been governed by democratically elected governments since 1982, when a long string of military coups came to an end. Presidents Hernán Siles Zuazo (1982–85) and Víctor Paz Estenssoro (1985–89) began a tradition of ceding power peacefully which has continued( SONY VGP-BPS9A battery) , although two presidents have stepped down in the face of popular protests: Gonzalo Sánchez de Lozada in 2003 and Carlos Mesa in 2005. Bolivia's multiparty democracy has seen a wide variety of parties in the presidency and parliament, although the Revolutionary Nationalist Movement, National Democratic Action( SONY VGP-BPS9A/B battery) , and the Revolutionary Left Movement predominated from 1985 to 2005. The current president is Evo Morales, the first indigenous Bolivian to serve as head of state. Morales' Movement for Socialism – Political Instrument for the Sovereignty of the Peoples party was the first to win an outright presidential majority in four decades, doing so both in 2005 and 2009( SONY VGP-BPS9/B battery) .The constitution, drafted in 2006-07 and approved in 2009, provides for balanced executive, legislative, judicial, and electoral powers, as well as several levels of autonomy. The traditionally strong executive branch tends to overshadow the Congress, whose role is generally limited to debating and approving legislation initiated by the executive( SONY VGP-BPS9A/S battery) . The judiciary, consisting of the Supreme Court and departmental and lower courts, has long been riddled with corruption and inefficiency. Through revisions to the constitution in 1994, and subsequent laws, the government has initiated potentially far-reaching reforms in the judicial system as well as increasing decentralizing powers to departments( SONY VGP-BPL9 battery) , municipalities, and indigenous territories.[edit]CapitalBolivia has its constitutionally recognized capital in Sucre, while La Paz is the seat of government, and is regularly described as the country's de facto capital. La Plata (now Sucre) was proclaimed provisional capital of the newly independent Alto Peru (later, Bolivia) on 1 July 1826.[78] On 12 July 1839( SONY VGP-BPS10 battery) , President José Miguel de Velasco proclaimed a law naming the city as the capital of Bolivia, and renaming it in honor of the revolutionary leader Antonio José de Sucre.[78] The Bolivian seat of government moved to La Paz at the turn of the twentieth century, as a consequence of Sucre's relative remoteness from economic activity after the decline of Potosí and its silver industry and of the Liberal Party in the War of 1899( SONY VGP-BPL10 battery) .The 2009 Constitution assigns the role of national capital to Sucre, not referring to La Paz in the text.[79] Nonetheless, the Palacio Quemado (the Presidential Palace and seat of Bolivian executive power) is located in La Paz, as are the National Congress and Plurinational Electoral Organ( SONY VGP-BPS11 battery) . La Paz thus continues to be the seat of government and de facto administrative capital.[edit]Executive branchFurther information: Cabinet of BoliviaThe executive branch is headed by a President and Vice President, and consists of a variable number (currently, 20) of government ministries. The president is elected to a five-year term by popular vote, and governs from the Presidential Palace (popularly called the Burnt Palace, Palacio Quemado) in La Paz( SONY VGP-BPL11 battery) . In the case that no candidate receives an absolute majority of the popular vote or more than 40% of the vote with an advantage of more than 10% over the second place finisher, a run-off is to be held among the two candidates most voted.[80][edit]PrisonsThere are 53 prisons in Bolivia which incarcerate around 8,700 people as of 2010. The prisons are managed by the Penitentiary Regime Directorate (Spanish( SONY VGP-BPL12 battery) : Dirección de Régimen Penintenciario). There are 17 prisons in departmental capital cities and 36 provincial prisons.[edit]Legislative branchThe Asamblea Legislativa Plurinacional (Plurinational Legislative Assembly or National Congress) has two chambers. The Cámara de Diputados (Chamber of Deputies) has 130 members elected to five year terms, seventy from single-member districts (circunscripciones), sixty by proportional representation( SONY VGP-BPS12 battery) , and seven by the minority indigenous peoples of seven departments. The Cámara de Senadores (Chamber of Senators) has 36 members (four per department). Members of the Assembly are elected to five year terms. The body has its headquarters on the Plaza Murillo in La Paz, but also holds honorary sessions elsewhere in Bolivia. The Vice President serves as titular head of the combined Assembly( SONY VGP-BPS13 battery) .[edit]Judicial branchThe judiciary consists of the Supreme Court, the Constitutional Tribunal, the Judiciary Council, Agrarian and Environmental Tribunal, and District (departmental) and lower courts.Plurinational Constitutional Tribunal (Spanish: Tribunal Constitucional Plurinacional) — rules on the constitutionality of government or court actions( SONY VGP-BPS13Q battery) Supreme Court or Supreme Tribunal of Justice (Spanish: Tribunal Supremo de Justicia)Agrarian and Environmental Tribunal (Spanish: Tribunal Agroambiental) — highest court authority in matters of agriculture and the environmentJudiciary Council (Spanish: Consejo de la Magistratura) — oversees the conduct of courts and judges, including misconduct and ethical violations( SONY VGP-BPS13A/Q battery) District Courts (one in each department)Provincial and local courtsIn October 2011, Bolivia will hold its first judicial elections to choose members of the national courts by popular vote.[edit]Electoral branchThe electoral branch of Bolivia's government, formally the Plurinational Electoral Organ, is an independent branch of government which replaced the National Electoral Court in 2010. The branch consists of the Supreme Electoral Tribunal( SONY VGP-BPS13B/Q battery) , the nine Departmental Electoral Tribunals, Electoral Judges, the anonymously selected Juries at Election Tables, and Electoral Notaries.[81] Wilfredo Ovando presides over the seven-member Supreme Electoral Tribunal. Its operations are mandated by the Constitution and regulated by the Electoral Regime Law (Law 026, passed 2010) ( SONY VGP-BPS13/B battery) . The Organ's first elections were the country's first judicial election in October 2011, and five municipal special elections held in 2011.[edit]MilitaryAn SK-105, the main battle tank of the Bolivian army.The Bolivian military comprises three branches: Ejército (Army), Naval (Navy) and Fuerza Aérea (Air Force). The legal age for voluntary admissions is 18; however, when the numbers are small the government recruits anyone as young as 14.[82] The tour of duty is generally 12 months( SONY VGP-BPS13B/B battery) . The Bolivian government annually spends $130 million on defense.[83]The Bolivian Army has around 31,500 men. There are six military regions (regiones militares—RMs) in the army. The Army is organized into ten divisions.Though it is landlocked Bolivia keeps a navy. The Bolivian Naval Force (Fuerza Naval Boliviana in Spanish) is a naval force about 5,000 strong in 2008. ( SONY VGP-BPS13A/S battery) The Bolivian Air Force ('Fuerza Aérea Boliviana' or 'FAB') has nine air bases, located at La Paz, Cochabamba, Santa Cruz, Puerto Suárez, Tarija, Villamontes, Cobija, Riberalta, and Roboré.[edit]Civil aviationSee also: List of airlines of Bolivia and List of airports in BoliviaThe General Directorate of Civil Aeronautics (Dirección General de Aeronáutica Civil—DGAC) formerly part of the FAB, administers a civil aeronautics school called the National Institute of Civil Aeronautics (Instituto Nacional de Aeronáutica Civil—INAC) ( SONY VGP-BPS21A/B battery) , and two commercial air transport services TAM and TAB.[edit]TAM (Transporte Aéreo Militar)'TAM – Transporte Aéreo Militar (the Bolivian Military Airline) is an airline based in La Paz, Bolivia. It is the civilian wing of the 'Fuerza Aérea Boliviana' (the Bolivian Air Force), operating passenger services to remote towns and communities in the North and Northeast of Bolivia( SONY VGP-BPS21B battery) . TAM (a.k.a. TAM Group 71) has been a part of the FAB since 1945.A similar airline serving the Beni Department with small planes is Línea Aérea Amaszonas,[85] using smaller planes than TAM.[edit]TAB (Transportes Aéreos Bolivianos)Although a civil transport airline, TAB – Transportes Aéreos Bolivianos, was created as a subsidiary company of the FAB in 1977. It is subordinate to the Air Transport Management (Gerencia de Transportes Aéreos) and is headed by an FAB general( SONY VGP-BPS21 battery) . TAB, a charter heavy cargo airline, links Bolivia with most countries of the Western Hemisphere; its inventory included a fleet of Hercules C130 aircraft. TAB was headquartered adjacent to El Alto International Airport. TAB also flew to Miami and Houston, with stops in Panama.[edit]CultureMain article: Culture of BoliviaSee also: Music of Bolivia and Public holidays in BoliviaBolivian children playing tarkaBolivian culture has been heavily influenced by the Quechua, the Aymara, as well as by the popular cultures of Latin America as a whole( SONY VGP-BPS21/S battery) .The cultural development is divided into three distinct periods: precolumbian, colonial, and republican. Important archaeological ruins, gold and silver ornaments, stone monuments, ceramics, and weavings remain from several important pre-Columbian cultures. Major ruins include Tiwanaku, El Fuerte de Samaipata, Incallajta, and Iskanawaya( SONY VGP-BPS13AS battery) . The country abounds in other sites that are difficult to reach and have seen little archaeological exploration.[68]The Diablada, dance primeval, typical and main of Carnival of Oruro a Masterpiece of the Oral and Intangible Heritage of Humanity since 2001 in Bolivia (File: Fraternidad Artística y Cultural "La Diablada"( SONY VGP-BPS13S battery) .The Spanish brought their own tradition of religious art which, in the hands of local native and mestizo builders and artisans, developed into a rich and distinctive style of architecture, painting, and sculpture known as "Mestizo Baroque". The colonial period produced not only the paintings of Pérez de Holguín, Flores, Bitti( SONY VGP-BPS13B/S battery) , and others but also the works of skilled but unknown stonecutters, woodcarvers, goldsmiths, and silversmiths. An important body of Native Baroque religious music of the colonial period was recovered in recent years and has been performed internationally to wide acclaim since 1994( SONY VGP-BPS13B/G battery) .[68]Bolivian artists of stature in the 20th century include Guzmán de Rojas, Arturo Borda, María Luisa Pacheco, Roberto Mamani Mamani, Alejandro Mario Yllanes, Alfredo Da Silva, and Marina Núñez del Prado, William Vega.Bolivia has a rich folklore. Its regional folk music is distinctive and varied. The "devil dances" at the annual carnival of Oruro are one of the great folkloric events of South America, as is the lesser known carnival at Tarabuco( SONY VGP-BPS14 battery) .[68] The best known of the various festivals found in the country is the "Carnaval de Oruro", which was among the first 19 "Masterpieces of the Oral and Intangible Heritage of Humanity", as proclaimed by the UNESCO in May 2001.Entertainment includes football, which is the most popular sport, as well as table football, which is played on street corners by both children and adults( SONY VGP-BPL14 battery) .Literacy class in the El Alto section of La Paz[edit]EducationMain article: Education in BoliviaUnder UNESCO standards, Bolivia has been declared free of illiteracy in 2008, making it the fourth country in Latin America with this status.[77]Bolivia has a wide variety of public and private universities. Among them: Universidad San Francisco Xavier de Chuquisaca USFX – Sucre, founded in 1624; Universidad Mayor de San Andres UMSA – La Paz, founded in 1830( SONY VGP-BPS14/B battery) ; Universidad Mayor de San Simon UMSS – Cochabamba, founded in 1832; Universidad Autónoma Gabriel René Moreno UAGRM – Santa Cruz de la Sierra, founded in 1880; Universidad Tecnica de Oruro UTO – Oruro, founded in 1892; Universidad Autónoma Tomás Frías UATF – Potosi, founded in 1892; Universidad Juan Misael Saracho UJMS – Tarija, founded in 1946( SONY VGP-BPS14/S battery) ; Universidad Católica Boliviana San Pablo UCB, founded in 1966; Universidad Técnica del Beni UTB – Trinidad, founded in 1967; Universidad Nur NUR, founded in 1982; Universidad Privada de Santa Cruz de la Sierra UPSA – Santa Cruz de la Sierra, founded in 1984; Universidad Nacional Siglo XX UNSXX – Llallagua, founded in 1986( SONY VGP-BPS14B battery) ; Universidad del Valle UNIVALLE -Cochabamba, founded in 1988; Universidad Privada Boliviana UPB, founded in 1993; Universidad Privada Franz Tamayo UPFT, founded in 1993 and Universidad Amazónica de Pando UAP – Cobija, founded in 1993.For the first time in Bolivian history, three indigenous universities were created: Universidad Aymara Tupac Katari UATK – La Paz, founded in 2009( SONY VGP-BPS22 battery) ; Universidad Quechua Casmiro Huanca UQCH – Cochabamba, founded in 2009 and Universidad Boliviana Guaraní y Pueblos de Tierras Bajas UGPTB – Chuquisaca, founded in 2009.
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