Carbon And Nitrogen

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with 12C and 13C being stable, while 14C is radioactive, decaying with a half-life of about 5,730 yearsSony VAIO VPCF135Z1E/B battery.[9] Carbon is one of the few elements known since antiquity.

There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon.[12] The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials knownSony VAIO VPCF137HG/BI battery, while graphite is soft enough to form a streak on paper (hence its name, from the Greek word "to write"). Diamond has a very low electrical conductivity, while graphite is a very good conductor. Under normal conditions, diamond has the highest thermal conductivity of all known materials.

All carbon allotropes are solids under normal conditions with graphite being the most thermodynamically stable formSony VAIO VPCF136FG/BI battery. They are chemically resistant and require high temperature to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and other transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peatSony VAIO VPCF135FG/B battery, oil and methane clathrates. Carbon forms more compounds than any other element, with almost ten million pure organic compounds described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions.[13]

Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is present in all known life formsSony VAIO VPCF127HG/BI battery, and in the human body carbon is the second most abundant element by mass (about 18.5%) after oxygen.[14] This abundance, together with the unique diversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered on Earth, make this element the chemical basis of all known lifeSony VAIO VPCF11Z1E battery.

Characteristics

The different forms or allotropes of carbon (see below) include the hardest naturally occurring substance, diamond, and also one of the softest known substances, graphite. Moreover, it has an affinity for bonding with other small atoms, including other carbon atoms, and is capable of forming multiple stable covalent bonds with such atomsSony VAIO VPCF11S1E battery. As a result, carbon is known to form almost ten million different compounds; the large majority of all chemical compounds.[13] Carbon also has the highest sublimation point of all elements. At atmospheric pressure it has no melting point as its triple point is at 10.8 ± 0.2 MPa and 4,600 ± 300 K (~4,330 °C or 7,820 °F),[2][3] so it sublimates at about 3,900 K. Sony VAIO VPCF11M1E/H battery

Carbon sublimes in a carbon arc which has a temperature of about 5,800 K (5,530 °C; 9,980 °F). Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest melting point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperatureSony VAIO VPCF11M1E battery.

Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizersSony VAIO VPCF11JFX/B battery. It does not react with sulfuric acid, hydrochloric acid, chlorine or any alkalis. At elevated temperatures carbon reacts with oxygen to form carbon oxides, and will reduce such metal oxides as iron oxide to the metal. This exothermic reaction is used in the iron and steel industry to control the carbon content of steel:

Fe3O4 + 4 C(s) → 3 Fe(s) + 4 CO(g)

with sulfur to form carbon disulfide and with steam in the coal-gas reactionSony VAIO VPCF119FJ battery:

C(s) + H2O(g) → CO(g) + H2(g).

Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel, and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools.

As of 2009, graphene appears to be the strongest material ever tested.[17] However, the process of separating it from graphite will require some technological development before it is economical enough to be used in industrial processesSony VAIO VPCF119FC/BI battery.[18]

The system of carbon allotropes spans a range of extremes:

Allotropes

Main article: Allotropes of carbon

Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structures with different molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Once considered exotic, fullerenes are nowadays commonly synthesized and used in researchSony VAIO VPCF119FC battery; they include buckyballs,[24][25] carbon nanotubes,[26] carbon nanobuds[27] and nanofibers.[28][29] Several other exotic allotropes have also been discovered, such as lonsdaleite,[30] glassy carbon,[31] carbon nanofoam[32] and linear acetylenic carbon (carbyne).[33]

The amorphous form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, which is essentially graphite but not held in a crystalline macrostructure. It is present as a powderSony VAIO VPCF117HG/BI battery, and is the main constituent of substances such as charcoal, lampblack (soot) and activated carbon. At normal pressures carbon takes the form of graphite, in which each atom is bonded trigonally to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons.[34] The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak van der Waals forcesSony VAIO VPCF116FG/BI battery. This gives graphite its softness and its cleaving properties (the sheets slip easily past one another). Because of the delocalization of one of the outer electrons of each atom to form a π-cloud, graphite conducts electricity, but only in the plane of each covalently bonded sheet. This results in a lower bulk electrical conductivity for carbon than for most metals. The delocalization also accounts for the energetic stability of graphite over diamond at room temperatureSony VAIO VPCF115FG/B battery.

Some allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d–f) fullerenes (C60, C540, C70); g) amorphous carbon; h) carbon nanotube.

At very high pressures carbon forms the more compact allotrope diamond, having nearly twice the density of graphite. Here, each atom is bonded tetrahedrally to four others, thus making a 3-dimensional network of puckered six-membered rings of atomsSony VAIO VPCF21ZHJ battery. Diamond has the same cubic structure as silicon and germanium and because of the strength of the carbon-carbon bonds, it is the hardest naturally occurring substance in terms of resistance to scratching. Contrary to the popular belief that "diamonds are forever", they are in fact thermodynamically unstable under normal conditions and transform into graphiteSony VAIO VPCF21Z1E/BI battery.[12] However, due to a high activation energy barrier, the transition into graphite is so extremely slow at room temperature as to be unnoticeable. Under some conditions, carbon crystallizes as lonsdaleite. This form has a hexagonal crystal lattice where all atoms are covalently bonded. Therefore, all properties of lonsdaleite are close to those of diamondSony VAIO VPCF21AHJ battery.[30]

Fullerenes have a graphite-like structure, but instead of purely hexagonal packing, they also contain pentagons (or even heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties of fullerenes (split into buckyballs, buckytubes and nanobuds) have not yet been fully analyzed and represent an intense area of research in nanomaterialsSony VAIO VPCF21AGJ battery. The names "fullerene" and "buckyball" are given after Richard Buckminster Fuller, popularizer of geodesic domes, which resemble the structure of fullerenes. The buckyballs are fairly large molecules formed completely of carbon bonded trigonally, forming spheroids (the best-known and simplest is the soccerball-shaped C60 buckminsterfullerene).[24] Carbon nanotubes are structurally similar to buckyballsSony VAIO VPCF21AFJ battery, except that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder.[25][26] Nanobuds were first reported in 2007 and are hybrid bucky tube/buckyball materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in a single structureSony VAIO VPCF219FJ/BI battery.[27]

Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in which the atoms are bonded trigonally in six- and seven-membered rings. It is among the lightest known solids, with a density of about 2 kg/m3Sony VAIO VPCF217HG/BI battery.[35] Similarly, glassy carbon contains a high proportion of closed porosity,[31] but contrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. Linear acetylenic carbon[33] has the chemical structure[33] -(C:::C)n-. Carbon in this modification is linear with sp orbital hybridization, and is a polymer with alternating single and triple bondsSony VAIO VPCF217HG battery. This type of carbyne is of considerable interest to nanotechnology as its Young's modulus is forty times that of the hardest known material – diamond.[36]

Occurrence

Graphite ore

Raw diamond crystal.

"Present day" (1990s) sea surface dissolved inorganic carbon concentration (from the GLODAP climatology)

Carbon is the fourth most abundant chemical element in the universe by mass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun, stars, comets, and in the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary diskSony VAIO VPCF14ZHJ battery. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.[37]

In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 810 gigatonnes of carbon) and dissolved in all water bodies (approximately 36,000 gigatonnes of carbon). Around 1,900 gigatonnes of carbon are present in the biosphereSony VAIO VPCF14AHJ battery. Hydrocarbons (such as coal, petroleum, and natural gas) contain carbon as well—coal "reserves" (not "resources") amount to around 900 gigatonnes, and oil reserves around 150 gigatonnes. Proven sources of natural gas are about 175 1012 cubic metres (representing about 105 gigatonnes carbon), but it is estimated that there are also about 900 1012 cubic metres of "unconventional" gas such as shale gasSony VAIO VPCF14AGJ battery, representing about 540 gigatonnes of carbon.[38] (In the past, quantities of hydrocarbons were greater. In the period from 1751 to 2008 about 347 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels.[39]) Carbon is also locked up as methane and methane hydrates in polar regions. It is estimated that at least 1,400 Gt of carbon is in this form just in (and under) the submarine permafrost of the Siberian ShelfSony VAIO VPCF14AFJ battery.[40]

Carbon is a major component in very large masses of carbonate rock (limestone, dolomite, marble and so on). Coal is the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil carbon fuel.[41] It is also rich in carbon – for example, anthracite contains 92–98%Sony VAIO VPCF149FJ/BI battery.[42]

As for individual carbon allotropes, graphite is found in large quantities in the United States (mostly in New York and Texas), Russia, Mexico, Greenland, and India. Natural diamonds occur in the rock kimberlite, found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Sierra LeoneSony VAIO VPCF148FJ/B battery. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. However, though diamonds are found naturally, about 30% of all industrial diamonds used in the U.S. are now made synthetically.

Carbon-14 is formed in upper layers of the troposphere and the stratosphereSony VAIO VPCF13ZHJ battery, at altitudes of 9–15 km, by a reaction that is precipitated by cosmic rays.[43] Thermal neutrons are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton.

Isotopes

Main article: Isotopes of carbon

Isotopes of carbon are atomic nuclei that contain six protons plus a number of neutrons (varying from 2 to 16). Carbon has two stable, naturally occurring isotopes.[9] The isotope carbon-12 (12C) forms 98.93% of the carbon on Earth, while carbon-13 (13C) forms the remaining 1.07%.Sony VAIO VPCF13Z0E/B battery [9] The concentration of 12C is further increased in biological materials because biochemical reactions discriminate against 13C.[44] In 1961 the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope carbon-12 as the basis for atomic weights.[45] Identification of carbon in NMR experiments is done with the isotope 13C.

Carbon-14 (14C) is a naturally occurring radioisotope which occurs in trace amounts on Earth of up to 1 part per trillion (0.0000000001%)Sony VAIO VPCF13M8E/B battery, mostly confined to the atmosphere and superficial deposits, particularly of peat and other organic materials.[46] This isotope decays by 0.158 MeV β- emission. Because of its relatively short half-life of 5730 years, 14C is virtually absent in ancient rocks, but is created in the upper atmosphere (lower stratosphere and upper troposphere) by interaction of nitrogen with cosmic raysSony VAIO VPCF13AHJ battery.[47] The abundance of 14C in the atmosphere and in living organisms is almost constant, but decreases predictably in their bodies after death. This principle is used in radiocarbon dating, invented in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000 years.[48][49]

There are 15 known isotopes of carbon and the shortest-lived of these is 8C which decays through proton emission and alpha decay and has a half-life of 1.98739x10−21 s. Sony VAIO VPCF13AGJ batteryThe exotic 19C exhibits a nuclear halo, which means its radius is appreciably larger than would be expected if the nucleus were a sphere of constant density.[51]

Formation in stars

Main articles: Triple-alpha process and CNO cycle

Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (helium nuclei) within the core of a giant or supergiant star which is known as the triple-alpha process, as the products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus produce lithium-5 and beryllium-8 respectivelySony VAIO VPCF13AFJ battery, both of which are highly unstable and decay almost instantly back into smaller nuclei.[52] This happens in conditions of temperatures over 100 megakelvin and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang. Instead, the interiors of stars in the horizontal branch transform three helium nuclei into carbon by means of this triple-alpha processSony VAIO VPCF138FJ/BI battery.[53] In order to be available for formation of life as we know it, this carbon must then later be scattered into space as dust, in supernova explosions, as part of the material which later forms second, third-generation star systems which have planets accreted from such dust.[54] The Solar System is one such third-generation star system. Another of the fusion mechanisms powering stars is the CNO cycle, in which carbon acts as a catalyst to allow the reaction to proceedSony VAIO VPCF138FJ/B battery.

Rotational transitions of various isotopic forms of carbon monoxide (for example, 12CO, 13CO, and C18O) are detectable in the submillimeter wavelength range, and are used in the study of newly forming stars in molecular clouds.[55]

Carbon cycle

Main article: Carbon cycle

Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions tonnes ("GtC" stands for gigatonnes of carbon; figures are circa 2004). The purple numbers indicate how much carbon moves between reservoirs each yearSony VAIO VPCF138FC/BI battery. The sediments, as defined in this diagram, do not include the ~70 million GtC of carbonate rock and kerogen.

Under terrestrial conditions, conversion of one element to another is very rare. Therefore, the amount of carbon on Earth is effectively constant. Thus, processes that use carbon must obtain it somewhere and dispose of it somewhere else. The paths that carbon follows in the environment make up the carbon cycleSony VAIO VPCF135FG battery. For example, plants draw carbon dioxide out of their environment and use it to build biomass, as in carbon respiration or the Calvin cycle, a process of carbon fixation. Some of this biomass is eaten by animals, whereas some carbon is exhaled by animals as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceansSony VAIO VPCF12AHJ battery; dead plant or animal matter may become petroleum or coal, which can burn with the release of carbon, should bacteria not consume it.[56][57]

Compounds

Organic compounds

Main article: Organic compound

Structural formula of methane, the simplest possible organic compound.

Correlation between the carbon cycle and formation of organic compounds. In plants, carbon dioxide formed by carbon fixation can join with water in photosynthesis (green) to form organic compounds, which can be used and further converted by both plants and animalsSony VAIO VPCF12AGJ battery.

Carbon has the ability to form very long chains of interconnecting C-C bonds. This property is called catenation. Carbon-carbon bonds are strong, and stable. This property allows carbon to form an almost infinite number of compounds; in fact, there are more known carbon-containing compounds than all the compounds of the other chemical elements combined except those of hydrogen (because almost all organic compounds contain hydrogen too) Sony VAIO VPCF12AFJ battery.

The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms. Chain length, side chains and functional groups all affect the properties of organic molecules. By IUPAC's definition, all the other organic compounds are functionalized compounds of hydrocarbons.Sony VAIO VPCF129FJ/BI battery

Carbon occurs in all known organic life and is the basis of organic chemistry. When united with hydrogen, it forms various hydrocarbons which are important to industry as refrigerants, lubricants, solvents, as chemical feedstock for the manufacture of plastics and petrochemicals and as fossil fuelsSony VAIO VPCF128FJ/B battery.

When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, lignans, chitins, alcohols, fats, and aromatic esters, carotenoids and terpenes. With nitrogen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids, and rubber productsSony VAIO VPCF127FJ/W battery. With the addition of phosphorus to these other elements, it forms DNA and RNA, the chemical-code carriers of life, and adenosine triphosphate (ATP), the most important energy-transfer molecule in all living cells.

Inorganic compounds

Main article: Compounds of carbon

Commonly carbon-containing compounds which are associated with minerals or which do not contain hydrogen or fluorine, are treated separately from classical organic compounds; however the definition is not rigid (see reference articles above) Sony VAIO VPCF11ZHJ battery. Among these are the simple oxides of carbon. The most prominent oxide is carbon dioxide (CO2). This was once the principal constituent of the paleoatmosphere, but is a minor component of the Earth's atmosphere today.[58] Dissolved in water, it forms carbonic acid (H2CO3), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstableSony VAIO VPCF11AHJ battery.[59] Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite. Carbon disulfide (CS2) is similar.

The other common oxide is carbon monoxide (CO). It is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower binding affinity.[60][61] Cyanide (CN–), has a similar structureSony VAIO VPCF11AGJ battery, but behaves much like a halide ion (pseudohalogen). For example it can form the nitride cyanogen molecule ((CN)2), similar to diatomic halides. Other uncommon oxides are carbon suboxide (C3O2),[62] the unstable dicarbon monoxide (C2O),[63][64] carbon trioxide (CO3),[65][66] cyclopentanepentone (C5O5)[67] cyclohexanehexone (C6O6),[67] and mellitic anhydride (C12O9) Sony VAIO VPCF11AFJ battery.

With reactive metals, such as tungsten, carbon forms either carbides (C4–), or acetylides (C2−

2) to form alloys with high melting points. These anions are also associated with methane and acetylene, both very weak acids. With an electronegativity of 2.5,[68] carbon prefers to form covalent bonds. A few carbides are covalent lattices, like carborundum (SiC), which resembles diamondSony VAIO VPCF118FJ battery.

Organometallic compounds

Main article: Organometallic chemistry

Organometallic compounds by definition contain at least one carbon-metal bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (for example, tetraethyllead), η2-alkene compounds (for example, Zeise's salt), and η3-allyl compounds (for example, allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands Sony VAIO VPCF117FJ battery (for example, ferrocene); and transition metal carbene complexes. Many metal carbonyls exist (for example, tetracarbonylnickel); some workers consider the carbon monoxide ligand to be purely inorganic, and not organometallic.

While carbon is understood to exclusively form four bonds, an interesting compound containing an octahedral hexacoordinated carbon atom has been reported. The cation of the compound is [(Ph3PAu)6C]2+Sony VAIO VGN-CS33H battery. This phenomenon has been attributed to the aurophilicity of the gold ligands.[69]

History and etymology

Antoine Lavoisier in his youth

The English name carbon comes from the Latin carbo for coal and charcoal,[70] whence also comes the French charbon, meaning charcoal. In German, Dutch and Danish, the names for carbon are Kohlenstoff, koolstof and kulstof respectively, all literally meaning coal-substance.

Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizationsSony VAIO VGN-CS33H/Z battery. Diamonds were known probably as early as 2500 BCE in China, while carbon in the form of charcoal was made around Roman times by the same chemistry as it is today, by heating wood in a pyramid covered with clay to exclude air.[71][72]

Carl Wilhelm Scheele

In 1722, René Antoine Ferchault de Réaumur demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon.[73] In 1772, Antoine Lavoisier showed that diamonds are a form of carbonSony VAIO VGN-CS33H/B battery; when he burned samples of charcoal and diamond and found that neither produced any water and that both released the same amount of carbon dioxide per gram. In 1779,[74] Carl Wilhelm Scheele showed that graphite, which had been thought of as a form of lead, was instead identical with charcoal but with a small admixture of iron, and that it gave "aerial acid" Sony VAIO VGN-CS31Z/Q battery (his name for carbon dioxide) when oxidized with nitric acid.[75] In 1786, the French scientists Claude Louis Berthollet, Gaspard Monge and C. A. Vandermonde confirmed that graphite was mostly carbon by oxidizing it in oxygen in much the same way Lavoisier had done with diamond.[76] Some iron again was left, which the French scientists thought was necessary to the graphite structureSony VAIO VGN-CS31S/W battery. However, in their publication they proposed the name carbone (Latin carbonum) for the element in graphite which was given off as a gas upon burning graphite. Antoine Lavoisier then listed carbon as an element in his 1789 textbook.[77]

A new allotrope of carbon, fullerene, that was discovered in 1985[78] includes nanostructured forms such as buckyballs and nanotubes.[24] Their discoverers – Robert Curl, Harold Kroto and Richard Smalley – received the Nobel Prize in Chemistry in 1996Sony VAIO VGN-CS31S/V battery.[79] The resulting renewed interest in new forms lead to the discovery of further exotic allotropes, including glassy carbon, and the realization that "amorphous carbon" is not strictly amorphous.[31]

Production

Graphite

Main article: Graphite

Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin, found in association with quartz, mica and feldspars in schistsSony VAIO VGN-CS31S/T battery, gneisses and metamorphosed sandstones and limestone as lenses or veins, sometimes of a meter or more in thickness. Deposits of graphite in Borrowdale, Cumberland, England were at first of sufficient size and purity that, until the 19th century, pencils were made simply by sawing blocks of natural graphite into strips before encasing the strips in woodSony VAIO VGN-CS31S/R battery. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.[80]

There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphous graphite is the lowest quality and most abundant. Contrary to science, in industry "amorphous" refers to very small crystal size rather than complete lack of crystal structureSony VAIO VGN-CS31S/P battery. Amorphous is used for lower value graphite products and is the lowest priced graphite. Large amorphous graphite deposits are found in China, Europe, Mexico and the United States. Flake graphite is less common and of higher quality than amorphous; it occurs as separate plates that crystallized in metamorphic rock. Flake graphite can be four times the price of amorphousSony VAIO VGN-CS28 battery. Good quality flakes can be processed into expandable graphite for many uses, such as flame retardants. The foremost deposits are found in Austria, Brazil, Canada, China, Germany and Madagascar. Vein or lump graphite is the rarest, most valuable, and highest quality type of natural graphite. It occurs in veins along intrusive contacts in solid lumps, and it is only commercially mined in Sri LankaSony VAIO VGN-CS28/Q battery.[80]

According to the USGS, world production of natural graphite was 1.1 million tonnes in 2010, to which China contributed 800,00 t, India 130,000 t, Brazil 76,000 t, North Korea 30,000 t and Canada 25,000 t. No natural graphite was reported mined in the United States, but 118,000 t of synthetic graphite with an estimated value of $998 million was produced in 2009Sony VAIO VGN-CS27 battery.[80]

Diamond

Main article: Diamond

Diamond output in 2005

The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world (see figure).

Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed in this process and subsequently the particles are sorted by densitySony VAIO VGN-CS27/W battery. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the oreSony VAIO VGN-CS27/R battery.[81]

Historically diamonds were known to be found only in alluvial deposits in southern India.[82] India led the world in diamond production from the time of their discovery in approximately the 9th century BCE[83] to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725. Sony VAIO VGN-CS27/P battery

Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after the discovery of the Diamond fields in South Africa. Production has increased over time and now an accumulated total of 4.5 billion carats have been mined since that date.[85] Interestingly 20% of that amount has been mined in the last 5 years alone and during the last ten years 9 new mines have started production while 4 more are waiting to be opened soonSony VAIO VGN-CS27/C battery. Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia.[85]

In the United States, diamonds have been found in Arkansas, Colorado and Montana.[86][87] In 2004, a startling discovery of a microscopic diamond in the United States[88] led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of MontanaSony VAIO VGN-CS26T/W battery.[89]

Today, most commercially viable diamond deposits are in Russia, Botswana, Australia and the Democratic Republic of Congo.[90] In 2005, Russia produced almost one-fifth of the global diamond output, reports the British Geological Survey. Australia has the richest diamantiferous pipe with production reaching peak levels of 42 metric tons (41 long tons; 46 short tons) per year in the 1990sSony VAIO VGN-CS26T/V battery.[86] There are also commercial deposits being actively mined in the Northwest Territories of Canada, Siberia (mostly in Yakutia territory; for example, Mir pipe and Udachnaya pipe), Brazil, and in Northern and Western Australia.

Applications

Pencil leads for mechanical pencils are made of graphite (often mixed with a clay or synthetic binder) Sony VAIO VGN-CS26T/T battery.

Sticks of vine and compressed charcoal.

A cloth of woven carbon filaments

Silicon carbide single crystal

The C60 fullerene in crystalline form

Tungsten carbide milling bits

Carbon is essential to all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon other than food and wood is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is used by the petrochemical industry to produce, amongst other things, gasoline and kerosene, through a distillation process, in refineriesSony VAIO VGN-CS26T/R battery. Cellulose is a natural, carbon-containing polymer produced by plants in the form of cotton, linen, and hemp. Cellulose is mainly used for maintaining structure in plants. Commercially valuable carbon polymers of animal origin include wool, cashmere and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chainSony VAIO VGN-CS26T/Q battery. The raw materials for many of these synthetic substances come from crude oil.

The uses of carbon and its compounds are extremely varied. It can form alloys with iron, of which the most common is carbon steel. Graphite is combined with clays to form the 'lead' used in pencils used for writing and drawing. It is also used as a lubricant and a pigment, as a molding material in glass manufactureSony VAIO VGN-CS26T/P battery, in electrodes for dry batteries and in electroplating and electroforming, in brushes for electric motors and as a neutron moderator in nuclear reactors.

Charcoal is used as a drawing material in artwork, for grilling, and in many other uses including iron smelting. Wood, coal and oil are used as fuel for production of energy and space heating. Gem quality diamond is used in jewelry, and Industrial diamonds are used in drillingSony VAIO VGN-CS26T/C battery, cutting and polishing tools for machining metals and stone. Plastics are made from fossil hydrocarbons, and carbon fiber, made by pyrolysis of synthetic polyester fibers is used to reinforce plastics to form advanced, lightweight composite materials. Carbon fiber is made by pyrolysis of extruded and stretched filaments of polyacrylonitrile (PAN) and other organic substancesSony VAIO VGN-CS25H battery. The crystallographic structure and mechanical properties of the fiber depend on the type of starting material, and on the subsequent processing. Carbon fibers made from PAN have structure resembling narrow filaments of graphite, but thermal processing may re-order the structure into a continuous rolled sheet. The result is fibers with higher specific tensile strength than steelSony VAIO VGN-CS25H/W battery.[91]

Carbon black is used as the black pigment in printing ink, artist's oil paint and water colours, carbon paper, automotive finishes, India ink and laser printer toner. Carbon black is also used as a filler in rubber products such as tyres and in plastic compounds. Activated charcoal is used as an absorbent and adsorbent in filter material in applications as diverse as gas masksSony VAIO VGN-CS25H/R battery, water purification and kitchen extractor hoods and in medicine to absorb toxins, poisons, or gases from the digestive system. Carbon is used in chemical reduction at high temperatures. Coke is used to reduce iron ore into iron. Case hardening of steel is achieved by heating finished steel components in carbon powder. Carbides of silicon, tungsten, boron and titaniumSony VAIO VGN-CS25H/Q battery, are among the hardest known materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interior surfaces in the built environment other than glass, stone and metalSony VAIO VGN-CS25H/P battery.

Diamonds

The diamond industry can be broadly separated into two basically distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways.

A large trade in gem-grade diamonds exists. Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commoditySony VAIO VGN-CS25H/C battery: there is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds.

The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds Sony VAIO VGN-CS23T/W battery (equal to about 100 million carats or 20 tonnes annually), unsuitable for use as gemstones and known as bort, are destined for industrial use.[92] In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 3 billion carats (600 tonnes) of synthetic diamond is produced annually for industrial useSony VAIO VGN-CS23T/Q battery.[93] The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applicationsSony VAIO VGN-CS23H battery.[94] Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil cell), high-performance bearings, and limited use in specialized windows.[95][96] With the continuing advances being made in the production of synthetic diamonds, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronicsSony VAIO VGN-CS23H/S battery.[97]

Precautions

Worker at carbon black plant in Sunray, Texas (photo by John Vachon, 1942)

Pure carbon has extremely low toxicity to humans and can be handled and even ingested safely in the form of graphite or charcoal. It is resistant to dissolution or chemical attack, even in the acidic contents of the digestive tract, for example. Consequently once it enters into the body's tissues it is likely to remain there indefinitelySony VAIO VGN-CS23H/B battery. Carbon black was probably one of the first pigments to be used for tattooing, and Ötzi the Iceman was found to have carbon tattoos that survived during his life and for 5200 years after his death.[98] However, inhalation of coal dust or soot (carbon black) in large quantities can be dangerous, irritating lung tissues and causing the congestive lung disease coalworker's pneumoconiosisSony VAIO VGN-CS23G battery. Similarly, diamond dust used as an abrasive can do harm if ingested or inhaled. Microparticles of carbon are produced in diesel engine exhaust fumes, and may accumulate in the lungs.[99] In these examples, the harmful effects may result from contamination of the carbon particles, with organic chemicals or heavy metals for example, rather than from the carbon itself.

Carbon generally has low toxicity to almost all life on Earth; however, to some creatures it can still be toxic – for instance, carbon nanoparticles are a deadly toxins to DrosophilaSony VAIO VGN-CS23G/W battery.[100]

Carbon may also burn vigorously and brightly in the presence of air at high temperatures, as in the Windscale fire, which was caused by sudden release of stored Wigner energy in the graphite core. Large accumulations of coal, which have remained inert for hundreds of millions of years in the absence of oxygen, may spontaneously combust when exposed to air, for example in coal mine waste tipsSony VAIO VGN-CS23G/Q battery.

The great variety of carbon compounds include such lethal poisons as tetrodotoxin, the lectin ricin from seeds of the castor oil plant Ricinus communis, cyanide (CN−) and carbon monoxide; and such essentials to life as glucose and protein.

Nitrogen ( /ˈnaɪtrɵdʒən/ ny-trə-jən) is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditionsSony VAIO VGN-CS23G/P battery, constituting 78.09% by volume of Earth's atmosphere.[1] The element nitrogen was discovered as a separable component of air, by Scottish physician Daniel Rutherford, in 1772.

Nitrogen is a common element in the universe, estimated at about seventh in total abundance in our galaxy and the solar system. Its occurrence there is thought to be entirely due to synthesis by fusion from carbon and hydrogen in supernovasSony VAIO VGN-CS21Z/Q battery. Due to the volatility of elemental nitrogen and its common compounds with hydrogen and oxygen, nitrogen is far less common on the rocky planets of the inner solar system, and it is a relatively rare element on Earth as a whole. However, as is the case on Earth, nitrogen and its compounds occur commonly as gases in the atmospheres of planets and moons that have atmospheresSony VAIO VGN-CS21S/W battery.

Many industrially important compounds, such as ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen dominates nitrogen chemistry, causing difficulty for both organisms and industry in breaking the bond to convert the N2 into useful compoundsSony VAIO VGN-CS21S/V battery, but at the same time causing release of large amounts of often useful energy when the compounds burn, explode, or decay back into nitrogen gas.

Nitrogen occurs in all living organisms, primarily in amino acids and thus proteins and in the nucleic acids (DNA and RNA). The human body contains about 3% by weight of nitrogen, the fourth most abundant element after oxygen, carbon, and hydrogen. Nitrogen resides in the chemical structure of almost all neurotransmittersSony VAIO VGN-CS21S/T battery, and is a defining component of alkaloids, biological molecules produced as secondary metabolites by many organisms. The nitrogen cycle describes movement of the element from the air into the biosphere and organic compounds, then back into the atmosphere. Synthetically produced nitrates are key ingredients of industrial fertilizers,[1] and key pollutants in causing the eutrophication of water systemsSony VAIO VGN-CS21S/R battery.

History and etymology

Nitrogen is formally considered to have been discovered by Scottish physician Daniel Rutherford in 1772, who called it noxious air or fixed air.[2] The fact that there was an element of air that does not support combustion was clear to Rutherford. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph PriestleySony VAIO VGN-CS21S/P battery, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as "mephitic air" or azote, from the Greek word ἄζωτος (azotos) meaning "lifeless".[3] In it, animals died and flames were extinguished. Lavoisier's name for nitrogen is used in many languages (French, Polish, Russian, etc.) and still remains in English in the common names of many compounds, such as hydrazine and compounds of the azide ionSony VAIO VGN-CS215J/R battery.

The English word nitrogen (1794) entered the language [4] from the French nitrogène, coined in 1790 by French chemist Jean-Antoine Chaptal (1756–1832), from "nitre" + Fr. gène "producing" (from Gk. -γενής means "forming" or "giving birth to."). The gas had been found in nitric acid. Chaptal's meaning was that nitrogen gas is the essential part of nitric acidSony VAIO VGN-CS215J/Q battery, in turn formed from saltpetre (potassium nitrate), then known as nitre. This word in the more ancient world originally described sodium salts that did not contain nitrate, and is a cognate of natron.

Nitrogen compounds were well known during the Middle Ages. Alchemists knew nitric acid as aqua fortis (strong water). The mixture of nitric and hydrochloric acids was known as aqua regia (royal water), celebrated for its ability to dissolve gold (the king of metals) Sony VAIO VGN-CS19/W battery. The earliest military, industrial, and agricultural applications of nitrogen compounds used saltpetre (sodium nitrate or potassium nitrate), most notably in gunpowder, and later as fertilizer. In 1910, Lord Rayleigh discovered that an electrical discharge in nitrogen gas produced "active nitrogen", an allotrope considered to be monatomic. The "whirling cloud of brilliant yellow light" produced by his apparatus reacted with quicksilver to produce explosive mercury nitrideSony VAIO VGN-CS19/R battery.[5]

[edit]Production

Nitrogen gas is an industrial gas produced by the fractional distillation of liquid air, or by mechanical means using gaseous air (i.e., pressurized reverse osmosis membrane or Pressure swing adsorption). Commercial nitrogen is often a byproduct of air-processing for industrial concentration of oxygen for steelmaking and other purposes. When supplied compressed in cylinders it is often called OFN (oxygen-free nitrogen) Sony VAIO VGN-CS19/Q battery.[6]

In a chemical laboratory it is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.

NH4Cl(aq) + NaNO2(aq) → N2(g) + NaCl(aq) + 2 H2O (l)

Small amounts of impurities NO and HNO3 are also formed in this reaction. The impurities can be removed by passing the gas through aqueous sulfuric acid containing potassium dichromate. Very pure nitrogen can be prepared by the thermal decomposition of barium or sodium azideSony VAIO VGN-CS19/P battery.

2 NaN3 → 2 Na + 3 N2

[edit]Properties

Nitrogen is a nonmetal, with an electronegativity of 3.04. It has five electrons in its outer shell and is, therefore, trivalent in most compounds. The triple bond in molecular nitrogen (N2) is one of the strongest. The resulting difficulty of converting N2 into other compounds, and the ease (and associated high energy release) of converting nitrogen compounds into elemental N2Sony VAIO VGN-CS17H/W battery, have dominated the role of nitrogen in both nature and human economic activities.

At atmospheric pressure molecular nitrogen condenses (liquefies) at 77 K (−195.79 °C) and freezes at 63 K (−210.01 °C)[1] into the beta hexagonal close-packed crystal allotropic form. Below 35.4 K (−237.6 °C) nitrogen assumes the cubic crystal allotropic form (called the alpha-phase). Liquid nitrogen, a fluid resembling water in appearanceSony VAIO VGN-CS17H/Q battery, but with 80.8% of the density (the density of liquid nitrogen at its boiling point is 0.808 g/mL), is a common cryogen.

Unstable allotropes of nitrogen consisting of more than two nitrogen atoms have been produced in the laboratory, like N3 and N4.[7] Under extremely high pressures (1.1 million atm) and high temperatures (2000 K), as produced using a diamond anvil cell, nitrogen polymerizes into the single-bonded cubic gauche crystal structure. This structure is similar to that of diamondSony VAIO VGN-CS16T/W battery, and both have extremely strong covalent bonds. N4 is nicknamed "nitrogen diamond."[8]

Other (as yet unsynthesized) allotropes include hexazine (N6, a benzene analog)[9] and octaazacubane (N8, a cubane analog).[10] The former is predicted to be highly unstable, while the latter is predicted to be kinetically stable, for reasons of orbital symmetrySony VAIO VGN-CS16T/T battery.[11]

[edit]Isotopes

See also: Isotopes of nitrogen

There are two stable isotopes of nitrogen: 14N and 15N. By far the most common is 14N (99.634%), which is produced in the CNO cycle in stars. Of the ten isotopes produced synthetically, 13N has a half-life of ten minutes and the remaining isotopes have half-lives on the order of seconds or less. Biologically mediated reactions (e.g., assimilation, nitrification, and denitrification) strongly control nitrogen dynamics in the soilSony VAIO VGN-CS16T/R battery. These reactions typically result in 15N enrichment of the substrate and depletion of the product.

A small part (0.73%) of the molecular nitrogen in Earth's atmosphere is the isotopologue 14N15N, and almost all the rest is 14N2.

Radioisotope 16N is the dominant radionuclide in the coolant of pressurized water reactors or boiling water reactors during normal operation. It is produced from 16O (in water) via (n,p) reactionSony VAIO VGN-CS16T/Q battery. It has a short half-life of about 7.1 s, but during its decay back to 16O produces high-energy gamma radiation (5 to 7 MeV).

Because of this, the access to the primary coolant piping in a pressurized water reactor must be restricted during reactor power operation.[12] 16N is one of the main means used to immediately detect even small leaks from the primary coolant to the secondary steam cycleSony VAIO VGN-CS16T/P battery.

In similar fashion, access to any of the steam cycle components in a boiling water reactor nuclear power plant must be restricted during operation. Condensate from the condenser is typically retained for 10 minutes to allow for decay of the 16N. This eliminates the need to shield and restrict access to any of the feed water piping or pumpsSony VAIO VGN-CS13T/W battery.

[edit]Electromagnetic spectrum

Nitrogen discharge (spectrum) tube

Molecular nitrogen (14N2) is largely transparent to infrared and visible radiation because it is a homonuclear molecule and, thus, has no dipole moment to couple to electromagnetic radiation at these wavelengths. Significant absorption occurs at extreme ultraviolet wavelengths, beginning around 100 nanometers. This is associated with electronic transitions in the molecule to states in which charge is not distributed evenly between nitrogen atomsSony VAIO VGN-CS13H/W battery. Nitrogen absorption leads to significant absorption of ultraviolet radiation in the Earth's upper atmosphere and the atmospheres of other planetary bodies. For similar reasons, pure molecular nitrogen lasers typically emit light in the ultraviolet range.

Nitrogen also makes a contribution to visible air glow from the Earth's upper atmosphere, through electron impact excitation followed by emissionSony VAIO VGN-CS13H/R battery. This visible blue air glow (seen in the polar aurora and in the re-entry glow of returning spacecraft) typically results not from molecular nitrogen but rather from free nitrogen atoms combining with oxygen to form nitric oxide (NO).

Nitrogen gas also exhibits scintillation.

[edit]Reactions

Structure of dinitrogen, N2

Structure of [Ru(NH3)5(N2)]2+

In general, nitrogen is unreactive at standard temperature and pressure. N2 reacts spontaneously with few reagents, being resilient to acids and bases as well as oxidants and most reductants. When nitrogen reacts spontaneously with a reagent, the net transformation is often called nitrogen fixationSony VAIO VGN-CS13H/Q battery.

Nitrogen reacts with elemental lithium.[13] Lithium burns in an atmosphere of N2 to give lithium nitride:

6 Li + N2 → 2 Li3N

Magnesium also burns in nitrogen, forming magnesium nitride.

3 Mg + N2 → Mg3N2

N2 forms a variety of adducts with transition metals. The first example of a dinitrogen complex is [Ru(NH3)5(N2)]2+ (see figure at right). However, it is interesting to note that the N2 ligand was obtained by the decomposition of hydrazine, and not coordination of free dinitrogen. Such compounds are now numerous, other examples include IrCl(N2)(PPh3)2Sony VAIO VGN-CS13H/P battery, W(N2)2(Ph2PCH2CH2PPh2)2, and [(η5-C5Me4H)2Zr]2(μ2, η2,η2-N2). These complexes illustrate how N2 might bind to the metal(s) in nitrogenase and the catalyst for the Haber process.[14] A catalytic process to reduce N2 to ammonia with the use of a molybdenum complex in the presence of a proton source was published in 2005.[13]

The starting point for industrial production of nitrogen compounds is the Haber processSony VAIO VGN-CS11Z/T battery, in which nitrogen is fixed by reacting N2 and H2 over an iron(II, III) oxide (Fe3O4) catalyst at about 500 °C and 200 atmospheres pressure. Biological nitrogen fixation in free-living cyanobacteria and in the root nodules of plants also produces ammonia from molecular nitrogen. The reaction, which is the source of the bulk of nitrogen in the biosphere, is catalyzed by the nitrogenase enzyme complex that contains Fe and Mo atomsSony VAIO VGN-CS11Z/R battery, using energy derived from hydrolysis of adenosine triphosphate (ATP) into adenosine diphosphate and inorganic phosphate (−20.5 kJ/mol).

[edit]Occurrence

See also Category: Nitrate minerals

See also Category: Ammonium minerals

Nitrogen is the largest constituent of the Earth's atmosphere (78.082% by volume of dry air, 75.3% by weight in dry air). However, this high concentration does not reflect nitrogen's overall low abundance in the makeup of the Earth, from which most of the element escaped by solar evaporation, early in the planet's formationSony VAIO VGN-CS11S/W battery.

Nitrogen is a common element in the universe, and is estimated to be approximately seventh most abundant chemical element by mass in the universe, our galaxy and the solar system. Its occurrence there is thought to be entirely due to synthesis by fusion from carbon and hydrogen in supernovas. In these places it was originally created by fusion processes from carbon and hydrogen in supernovasSony VAIO VGN-CS11S/Q battery.[15]Molecular nitrogen and nitrogen compounds have been detected in interstellar space by astronomers using the Far Ultraviolet Spectroscopic Explorer.[16]

Due to the volatility of elemental nitrogen and also its common compounds with hydrogen and oxygen, nitrogen and its compounds were driven out of the planetesimals in the early solar system by the heat of the Sun, and in the form of gases, were lost to the rocky planets of the inner solar system. Nitrogen is therefore a relatively rare element on these inner planetsSony VAIO VGN-CS11S/P battery, including Earth, as a whole. In this, nitrogen resembles neon, which has a similar abundance in the universe, but is also rare in the inner solar system. Nitrogen is estimated at 30th of the elements in crustal abundance. There exist some relatively uncommon nitrogen minerals, such as saltpetre (potassium nitrate), Chile saltpetre (sodium nitrate) and sal ammoniac (ammonium chloride) (Sony VAIO VGN-AW11M/H battery). Even these are known mainly as concentrated from evaporative ocean beds, on account of their ready solubility of most naturally-occurring nitrogen compounds in water. A similar pattern occurs with the water solubility of the uncommon light element boron.

However, nitrogen and its compounds occur far more commonly as gases in the atmospheres of planets and moons that are large enough to have atmospheres.[17] For example, molecular nitrogen is a major constituent of not only Earth's atmosphere(Sony VAIO VGN-AW11S/B battery), but also the Saturnian moon Titan's thick atmosphere. Also, due to retension by gravity at colder temperatures, nitrogen and its compounds occur in appreciable to trace amounts in planetary atmospheres of the gas giant planets.[18]

Nitrogen is present in all living organisms, in proteins, nucleic acids, and other molecules. It typically makes up around 4% of the dry weight of plant matter, and around 3% of the weight of the human body(Sony VAIO VGN-AW11Z/B battery). It is a large component of animal waste (for example, guano), usually in the form of urea, uric acid, ammonium compounds, and derivatives of these nitrogenous products, which are essential nutrients for all plants that cannot fix atmospheric nitrogen.

[edit]Compounds

See also Category: Nitrogen compounds

The main neutral hydride of nitrogen is ammonia (NH3), although hydrazine (N2H4) is also commonly used. Ammonia is more basic than water by 6 orders of magnitude. In solution ammonia forms the ammonium ion (Sony VAIO VGN-AW170C battery)(NH+4). Liquid ammonia (boiling point 240 K) is amphiprotic (displaying either Brønsted-Lowry acidic or basic character) and forms ammonium and the less common amide ions (NH−

2); both amides and nitride (N3−) salts are known, but decompose in water. Singly, doubly, triply and quadruply substituted alkyl compounds of ammonia are called amines (four substitutions, to form commercially and biologically important quaternary amines, results in a positively charged nitrogen, and thus a water-soluble, or at least amphiphilic, compound) (Sony VAIO VGN-AW19/Q battery). Larger chains, rings and structures of nitrogen hydrides are also known, but are generally unstable.

Other classes of nitrogen anions (negatively charged ions) are the poisonous azides (N−

3), which are linear and isoelectronic to carbon dioxide, but which bind to important iron-containing enzymes in the body in a manner more resembling cyanide. Another molecule of the same structure is the colorless and relatively inert anesthetic gas Nitrous oxide (dinitrogen monoxide, N2O), also known as laughing gas(Sony VAIO VGN-AW19 battery). This is one of a variety of nitrogen oxides that form a family often abbreviated as NOx. Nitric oxide (nitrogen monoxide, NO), is a natural free radical used in signal transduction in both plants and animals, for example, in vasodilation by causing the smooth muscle of blood vessels to relax. The reddish and poisonous nitrogen dioxide NO2 contains an unpaired electron and is an important component of smog(Sony VAIO VGN-AW21M/H battery). Nitrogen molecules containing unpaired electrons show a tendency to dimerize (thus pairing the electrons), and are, in general, highly reactive. The corresponding acids are nitrous HNO2 and nitric acid HNO3, with the corresponding salts called nitrites and nitrates.

The higher oxides dinitrogen trioxide N2O3, dinitrogen tetroxide N2O4 and dinitrogen pentoxide N2O5, are unstable and explosive, a consequence of the chemical stability of N2. Nearly every hypergolic rocket engine uses N2O4 as the oxidizer(Sony VAIO VGN-AW21S/B battery); their fuels, various forms of hydrazine, are also nitrogen compounds. These engines are extensively used on spacecraft such as the space shuttle and those of the Apollo Program because their propellants are liquids at room temperature and ignition occurs on contact without an ignition system, allowing many precisely controlled burns. Some launch vehicles such as the Titan II and Ariane 1 through 4 also use hypergolic fuels(Sony VAIO VGN-AW21VY/Q battery), although the trend is away from such engines for cost and safety reasons. N2O4 is an intermediate in the manufacture of nitric acid HNO3, one of the few acids stronger than hydronium and a fairly strong oxidizing agent.

Nitrogen is notable for the range of explosively unstable compounds that it can produce. Nitrogen triiodide NI3 is an extremely sensitive contact explosive. Nitrocellulose, produced by nitration of cellulose with nitric acid, is also known as guncotton(Sony VAIO VGN-AW21XY/Q battery). Nitroglycerin, made by nitration of glycerin, is the dangerously unstable explosive ingredient of dynamite. The comparatively stable, but less powerful explosive trinitrotoluene (TNT) is the standard explosive against which the power of nuclear explosions are measured.[19]

Nitrogen can also be found in organic compounds. Common nitrogen functional groups include: amines, amides, nitro groups, imines, and enamines(Sony VAIO VGN-AW21Z/B battery). The amount of nitrogen in a chemical substance can be determined by the Kjeldahl method.

[edit]Applications

Nitrogen gas has a variety of applications, including serving as an inert replacement for air where oxidation is undesirable;

As a modified atmosphere, pure or mixed with carbon dioxide, to preserve the freshness of packaged or bulk foods (by delaying rancidity and other forms of oxidative damage)

In ordinary incandescent light bulbs as an inexpensive alternative to argon.[20]

The production of electronic parts such as transistors, diodes, and integrated circuits

Dried and pressurized, as a dielectric gas for high-voltage equipment(Sony VAIO VGN-AW230J/H battery)

The manufacturing of stainless steel[21]

Used in military aircraft fuel systems to reduce fire hazard, (see inerting system)

On top of liquid explosives as a safety measure

Filling automotive and aircraft tires[22] due to its inertness and lack of moisture or oxidative qualities, as opposed to air. The difference in N2 content between air and pure N2 is 20%[23][24]

Used as a propellant for draft wine, and as an alternative to or together with carbon dioxide for other beverages(Sony VAIO VGN-AW235J/B battery).

Nitrogen is commonly used during sample preparation procedures for chemical analysis. It is used to concentrate and reduce the volume of liquid samples. Directing a pressurized stream of nitrogen gas perpendicular to the surface of the liquid allows the solvent to evaporate while leaving the solute(s) and un-evaporated solvent behind(Sony VAIO VGN-AW270Y/Q battery).[25]

Nitrogen tanks are also replacing carbon dioxide as the main power source for paintball guns. Nitrogen must be kept at higher pressure than CO2, making N2 tanks heavier and more expensive.

[edit]Nitrogenated beer

Nitrogen can be used instead of carbon dioxide to pressurize kegs of some beers, in particular, stouts and British ales, due to the smaller bubbles it produces, which makes the dispensed beer smoother and headier(Sony VAIO VGN-AW31M/H battery). A pressure sensitive nitrogen capsule known commonly as a "widget" allows nitrogen charged beers to be packaged in cans and bottles.[26]

A mixture of nitrogen and carbon dioxide can be used for this purpose as well, to maintain the saturation of beer with carbon dioxide.[27]

[edit]Liquid nitrogen

Air balloon submerged in liquid nitrogen

Main article: Liquid nitrogen

Liquid nitrogen is a cryogenic liquid. At atmospheric pressure, it boils at −195.8 °C. When insulated in proper containers such as Dewar flasks, it can be transported without much evaporative loss(Sony VAIO VGN-AW31S/B battery).[28]

Like dry ice, the main use of liquid nitrogen is as a refrigerant. Among other things, it is used in the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials. It is used in the clinical setting in cryotherapy to remove cysts and warts on the skin.[29] It is used in cold traps for certain laboratory equipment and to cool infrared detectors or X-ray detectors(Sony VAIO VGN-AW31XY/Q battery). It has also been used to cool central processing units and other devices in computers that are overclocked, and that produce more heat than during normal operation.[30]

[edit]Applications of nitrogen compounds

Molecular nitrogen (N2) in the atmosphere is relatively non-reactive due to its strong bond, and N2 plays an inert role in the human body, being neither produced nor destroyed. In nature, nitrogen is converted into biologically (and industrially) useful compounds by lightning, and by some living organisms, notably certain bacteria(Sony VAIO VGN-AW31ZJ/B battery) (i.e., nitrogen fixing bacteria—see Biological role below). Molecular nitrogen is released into the atmosphere in the process of decay, in dead plant and animal tissues.

The ability to combine, or fix, molecular nitrogen is a key feature of modern industrial chemistry, where nitrogen and natural gas are converted into ammonia via the Haber process. Ammonia, in turn, can be used directly (primarily as a fertilizer, and in the synthesis of nitrated fertilizers) (Sony VAIO VGN-AW41JF/H battery),[1] or as a precursor of many other important materials including explosives, largely via the production of nitric acid by the Ostwald process.

The organic and inorganic salts of nitric acid have been important historically as convenient stores of chemical energy. They include important compounds such as potassium nitrate (or saltpeter used in gunpowder) and ammonium nitrate(Sony VAIO VGN-AW41JF battery), an important fertilizer and explosive (see ANFO). Various other nitrated organic compounds, such as nitroglycerin, trinitrotoluene, and nitrocellulose, are used as explosives and propellants for modern firearms. Nitric acid is used as an oxidizing agent in liquid fueled rockets. Hydrazine and hydrazine derivatives find use as rocket fuels and monopropellants. In most of these compounds(Sony VAIO VGN-AW41MF/H battery), the basic instability and tendency to burn or explode is derived from the fact that nitrogen is present as an oxide, and not as the far more stable nitrogen molecule (N2), which is a product of the compounds' thermal decomposition. When nitrates burn or explode, the formation of the powerful triple bond in the N2 produces most of the energy of the reaction(Sony VAIO VGN-AW41MF battery).

Nitrogen is a constituent of molecules in every major drug class in pharmacology and medicine. Nitrous oxide (N2O) was discovered early in the 19th century to be a partial anesthetic, though it was not used as a surgical anesthetic until later. Called "laughing gas", it was found capable of inducing a state of social disinhibition resembling drunkenness(Sony VAIO VGN-AW41XH/Q battery). Other notable nitrogen-containing drugs are drugs derived from plant alkaloids, such as morphine (there exist many alkaloids known to have pharmacological effects; in some cases, they appear as natural chemical defenses of plants against predation). Drugs that contain nitrogen include all major classes of antibiotics and organic nitrate drugs like nitroglycerin and nitroprusside that regulate blood pressure and heart action by mimicking the action of nitric oxide(Sony VAIO VGN-AW41XH battery).

[edit]Biological role

See also: Nitrogen cycle and Human impacts on the nitrogen cycle

Nitrogen is an essential building block of amino and nucleic acids, essential to life on Earth.

Elemental nitrogen in the atmosphere cannot be used directly by either plants or animals, and must be converted to a reduced (or 'fixed') state to be useful for higher plants and animals. Precipitation often contains substantial quantities of ammonium and nitrate, thought to result from nitrogen fixation by lightning and other atmospheric electric phenomena(Sony VAIO VGN-AW41ZF/B battery).[31] This was first proposed by Liebig in 1827 and later confirmed.[31] However, because ammonium is preferentially retained by the forest canopy relative to atmospheric nitrate, most fixed nitrogen reaches the soil surface under trees as nitrate. Soil nitrate is preferentially assimilated by tree roots relative to soil ammonium[citation needed].

Specific bacteria (e.g., Rhizobium trifolium) (Sony VAIO VGN-AW41ZF battery) possess nitrogenase enzymes that can fix atmospheric nitrogen (see nitrogen fixation) into a form (ammonium ion) that is chemically useful to higher organisms. This process requires a large amount of energy and anoxic conditions. Such bacteria may live freely in soil (e.g., Azotobacter) but normally exist in a symbiotic relationship in the root nodules of leguminous plants (SONY Vaio VGN-NS38M Battery) (e.g. clover, Trifolium, or soybean plant, Glycine max). Nitrogen-fixing bacteria are also symbiotic with a number of unrelated plant species such as alders (Alnus) spp., lichens, Casuarina, Myrica, liverworts, and Gunnera.[32]

As part of the symbiotic relationship, the plant converts the 'fixed' ammonium ion to nitrogen oxides and amino acids to form proteins and other molecules, (e.g., alkaloids). In return for the 'fixed' nitrogen, the plant secretes sugars to the symbiotic bacteria(SONY Vaio VGN-NS31S Battery).[32] Legumes maintain an anaerobic (oxygen free) environment for their nitrogen-fixing bacteria.

Plants are able to assimilate nitrogen directly in the form of nitrates that may be present in soil from natural mineral deposits, artificial fertilizers, animal waste, or organic decay (as the product of bacteria, but not bacteria specifically associated with the plant). Nitrates absorbed in this fashion are converted to nitrites by the enzyme nitrate reductase(SONY Vaio VGN-NS31M Battery), and then converted to ammonia by another enzyme called nitrite reductase.[32]

Nitrogen compounds are basic building blocks in animal biology as well. Animals use nitrogen-containing amino acids from plant sources as starting materials for all nitrogen-compound animal biochemistry, including the manufacture of proteins and nucleic acids. Plant-feeding insects are dependent on nitrogen in their diet(SONY Vaio VGN-NS31Z Battery), such that varying the amount of nitrogen fertilizer applied to a plant can affect the reproduction rate of insects feeding on fertilized plants.[33]

Soluble nitrate is an important limiting factor in the growth of certain bacteria in ocean waters.[34] In many places in the world, artificial fertilizers applied to crop-lands to increase yields result in run-off delivery of soluble nitrogen to oceans at river mouths(SONY Vaio VGN-NS21Z Battery). This process can result in eutrophication of the water, as nitrogen-driven bacterial growth depletes water oxygen to the point that all higher organisms die. Well-known "dead zone" areas in the U.S. Gulf Coast and the Black Sea are due to this important polluting process.

Many saltwater fish manufacture large amounts of trimethylamine oxide to protect them from the high osmotic effects of their environment; conversion of this compound to dimethylamine is responsible for the early odor in unfresh saltwater fish(SONY Vaio VGN-NS21M Battery).[35] In animals, free radical nitric oxide (NO) (derived from an amino acid), serves as an important regulatory molecule for circulation.[34]

Animal metabolism of NO results in production of nitrite. Animal metabolism of nitrogen in proteins, in general, results in excretion of urea, while animal metabolism of nucleic acids results in excretion of urea and uric acid. The characteristic odor of animal flesh decay is caused by the creation of long-chain, nitrogen-containing amines, such as putrescine and cadaverine(SONY Vaio VGN-NS21S Battery), which are breakdown products of the amino acids ornithine and lysine, respectively, in decaying proteins.[36]

Decay of organisms and their waste products may produce small amounts of nitrate, but most decay eventually returns nitrogen content to the atmosphere, as molecular nitrogen. The circulation of nitrogen from atmosphere, to organic compounds, then back to the atmosphere, is referred to as the nitrogen cycle(SONY Vaio VGN-NS12S Battery).[32]

[edit]Safety

Rapid release of nitrogen gas into an enclosed space can displace oxygen, and therefore represents an asphyxiation hazard. This may happen with few warning symptoms, since the human carotid body is a relatively slow and a poor low-oxygen (hypoxia) sensing system.[37] An example occurred shortly before the launch of the first Space Shuttle mission in 1981(SONY Vaio VGN-NS12M Battery), when two technicians lost consciousness (and one of them died) after they walked into a space located in the Shuttle's Mobile Launcher Platform that was pressurized with pure nitrogen as a precaution against fire. The technicians would have been able to exit the room if they had experienced early symptoms from nitrogen-breathing(SONY Vaio VGN-NS11Z Battery).

When inhaled at high partial pressures (more than about 4 bar, encountered at depths below about 30 m in scuba diving), nitrogen begins to act as an anesthetic agent. It can cause nitrogen narcosis, a temporary semi-anesthetized state of mental impairment similar to that caused by nitrous oxide. (SONY Vaio VGN-NS11M Battery)

Nitrogen also dissolves in the bloodstream and body fats. Rapid decompression (in particular, in the case of divers ascending too quickly, or astronauts decompressing too quickly from cabin pressure to spacesuit pressure) can lead to a potentially fatal condition called decompression sickness (formerly known as caisson sickness or the bends) (SONY Vaio VGN-NS11L Battery), when nitrogen bubbles form in the bloodstream, nerves, joints, and other sensitive or vital areas.[40][41] Other "inert" gases (those gases other than carbon dioxide and oxygen) cause the same effects from bubbles composed of them, so replacement of nitrogen in breathing gases may prevent nitrogen narcosis, but does not prevent decompression sickness(SONY Vaio VGN-NS11J Battery).[42]

Direct skin contact with liquid nitrogen will cause severe frostbite (cryogenic "burns"). This may happen almost instantly on contact, or after a second or more, depending on the form of liquid nitrogen. Bulk liquid nitrogen causes less rapid freezing than a spray of nitrogen mist (such as is used to freeze certain skin growths in the practice of dermatology) (SONY Vaio VGN-NS11E Battery). The extra surface area provided by nitrogen-soaked materials is also important, with soaked clothing or cotton causing far more rapid damage than a spill of direct liquid to skin. Full "contact" between naked skin and large collected-droplets or pools of liquid nitrogen may be prevented for a second or two, by a layer of insulating gas from the Leidenfrost effect(SONY Vaio VGN-NS10L Battery). This may give the skin a second of protection from nitrogen bulk liquid. However, liquid nitrogen applied to skin in mists, and on fabrics, bypasses this effect, and causes local frostbite immediately.

Oxygen sensors are sometimes used as a safety precaution when working with liquid nitrogen to alert workers of gas spills into a confined space(SONY Vaio VGN-NS10J Battery).