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{{Infobox carbon}}
'''Carbon''' ({{pronEng|ˈkɑrbən}}) is a [[chemical element]] with the [[chemical symbol|symbol]] '''C''' and [[atomic number]] 6. It is a [[group 14]], [[nonmetal]]lic, [[tetravalence|tetravalent]] element, that presents several [[Allotropes of carbon|allotropic forms]] of which the best known are graphite (the [[Thermodynamic equilibrium|thermodynamically stable]] form under [[normal conditions]]), [[diamond]], and amorphous carbon.<ref name="therm prop">{{cite web |url=http://invsee.asu.edu/nmodules/Carbonmod/point.html |title=World of Carbon |accessdate=2007-12-21}}</ref> There are three naturally occurring [[isotopes]]: [[Carbon-12|<sup>12</sup>C]]  and [[Carbon-13|<sup>13</sup>C]] are stable, and [[Carbon-14|<sup>14</sup>C]] is [[radioactive]], decaying with a [[half-life]] of about 5700 years.<ref name="isotopes">{{cite web|url=http://www.webelements.com/webelements/elements/text/C/isot.html|title=Carbon - Naturally occurring isotopes|publisher=WebElements Periodic Table|accessdate=2007-12-08}}</ref> Carbon is one of the [[Discoveries of the chemical elements|few elements known to man since antiquity]].<ref>{{cite web |url=http://www.chemicalelements.com/show/dateofdiscovery.html |title=Periodic Table: Date of Discovery|accessdate=2007-03-13}}</ref><ref name=D2>{{cite web |url=http://chemistry.about.com/library/das/aa030303a.htm |title=Timeline of Element Discovery|accessdate=2007-03-13}}</ref> The name "carbon" comes from Latin language ''carbo'', coal, and in some Romance languages, the word carbon can refer both to the element and to coal.

It is the [[Abundance of the chemical elements|fourth most abundant element in the universe by mass]] after [[hydrogen]], [[helium]], and [[oxygen]]. It is present in all known [[life]]forms, and in the human body it is the second most abundant element by mass (about 18.5%) after oxygen.<ref>{{cite web |url=http://www.daviddarling.info/encyclopedia/E/elbio.html|title=Biological Abundance of Elements |accessdate=2007-12-06}}</ref> 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 [[life]].

The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is [[Opacity (optics)|opaque]] and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper. Diamond has a very low electric conductivity, while graphite is a very good conductor. Also, diamond has the highest thermal conductivity of [[List of thermal conductivities|all known materials]] under normal conditions. All the allotropic forms are solids under [[normal conditions]].

All forms of carbon are highly stable, requiring 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, peat, [[oil]] and [[methane clathrate]]s. Carbon forms more [[chemical compound|compounds]] than any other element, with almost ten million pure [[organic compound]]s described to date, which in turn are a tiny fraction of such compounds that are theoretically possible under standard conditions.<ref name=lanl>{{cite web|author=Chemistry Operations|date=[[December 15]], [[2003]]|url=http://periodic.lanl.gov/elements/6.html|title=Carbon|publisher=Los Alamos National Laboratory|accessdate=2007-11-21}}</ref>

== Characteristics==
Carbon exhibits remarkable properties, some paradoxical. Its different forms or ''[[allotropes]]'' (see below) include the hardest naturally occurring substance (diamond) and also one of the softest substances (graphite) known. Moreover, it has a great affinity for [[chemical bond|bonding]] with other small [[atom]]s, including other carbon atoms, and is capable of forming multiple stable [[covalent]] bonds with such atoms. Because of these properties, carbon is known to form nearly ten million different compounds, the large majority of all [[chemical compounds]].<ref name=lanl>{{cite web
 | author=Chemistry Operations
 | date=[[December 15]], [[2003]]
 | url=http://periodic.lanl.gov/elements/6.html
 | title=Carbon
 | publisher=Los Alamos National Laboratory
 | accessdate=2007-11-21
}}
</ref> Moreover, carbon has the highest [[melting point|melting]]/[[sublimation (chemistry)|sublimation]] point of all elements. At atmospheric pressure it has no actual melting point as its [[triple point]] is at 10 MPa (100 [[bar (unit)|bar]]) so it sublimates above 4000 K. Carbon sublimes in a carbon arc which has a temperature of about 5800K. 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 temperature.

Carbon compounds form the basis of all 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 oxidizers. 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:<br>
{{chem|Fe|3|O|4}} + 4C<sub>(s)</sub> → 3Fe<sub>(s)</sub> + 4CO<sub>(g)</sub><br>
with [[sulfur]] to form [[carbon disulfide]] and with steam in the coal-gas reaction<br>
C<sub>(s)</sub> + H<sub>2</sub>O<sub>(g)</sub> → CO<sub>(g)</sub> + H<sub>2(g)</sub>.<br> 
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. 

The system of carbon allotropes spans a range of extremes:
{| class="wikitable"
|style="width: 50%;"| Synthetic diamond nanorods are the hardest materials known.
| Graphite is one of the softest materials known.
|-
| Diamond is the ultimate abrasive.
| Graphite is a very good lubricant.
|-
| Diamond is an excellent electrical insulator.
| Graphite is a conductor of electricity.
|-
| Diamond is the best known thermal conductor
| Some forms of graphite are used for thermal insulation (i.e. firebreaks and heatshields)
|-
| Diamond is highly transparent.
| Graphite is opaque.
|-
| Diamond crystallizes in the cubic system.
| Graphite crystallizes in the hexagonal system.
|-
| Amorphous carbon is completely isotropic.
| Carbon nanotubes are among the most anisotropic materials ever produced.
|}

=== Allotropes ===
{{main|Allotropes of carbon}}
Atomic carbon is a very short-lived specie 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 research; they include buckyballs,<ref name="buckyballs"/><ref name="nanotubes">{{citebook|editor=Ebbesen, TW |year=1997 |title=Carbon nanotubes—preparation and properties |publisher=CRC Press|location=Boca Raton, Florida}}</ref> carbon nanotubes,<ref name="nanotubes2">{{cite journal |editor=MS Dresselhaus, G Dresselhaus, Ph Avouris |year=2001 |title=Carbon nanotubes: synthesis, structures, properties and applications |journal=Topics in Applied Physics |volume=80 |co-authors= Springer, Heidelberg}}</ref> carbon nanobuds<ref name="nanobuds">{{cite journal |co-authors=Nasibulin AG, Pikhitsa PV, Jiang H, et al. |year=2007 |title=A novel hybrid carbon material |journal=Nature Nanotechnology |volume=2 |pages=156-161}}</ref> and nanofibers,<ref>{{cite journal |co-authors=Nasibulin AG, Anisimov AS, Pikhitsa PV, et al. |year=2007 |title=Investigations of NanoBud formation |journal=Chemical Physics Letters |volume=446 |pages=109-114}}</ref>.<ref>{{cite journal |co-authors=R Vieiraa, M-J Ledouxa and C Pham-Huu |year=2004 |title=Synthesis and characterisation of carbon nanofibres with macroscopic shaping formed by catalytic decomposition of C2H6/H2 over nickel catalyst |journal=Applied Catalysis A |volume=274 |pages=1-8}}</ref> Several other exotic allotropes have also been discovered, such as  aggregated diamond nanorods,<ref>{{cite web |url=http://physicsweb.org/articles/news/9/8/16/1?rss=2.0 |title=Diamonds are not forever |publisher=physicsweb.org |accessdate=2007-12-21}}</ref> lonsdaleite,<ref name="lonsdaletite">{{cite journal |co-authors=Frondel, C and Marvin UB |year=1967 |title=Lonsdaleite, a new hexagonal polymorph of diamond |journal=Nature |volume=214 |page=587–589}}</ref> glassy carbon,<ref name="glassy carbon"/> carbon nanofoam<ref>{{cite journal |co-authors=Rode AV, Hyde ST, Gamaly EG, et al. |year=1999 |title=Structural analysis of a carbon foam formed by high pulse-rate laser ablation |journal=Applied Physics A-Materials Science & Processing |volume=69 |pages=S755-S758}}</ref> and linear acetylenic carbon.<ref name=LAC>Carbyne and Carbynoid Structures Series: Physics and Chemistry of Materials with Low-Dimensional Structures, Vol.  21 Heimann, R.B.; Evsyukov, S.E.; Kavan, L. (Eds.) 1999, 452 p., Hardcover ISBN 0-7923-5323-4</ref>

*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 powder, 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 hydrocarbon]]s. The resulting network is 2-dimensional, and the resulting flat sheets are stacked and loosely bonded through weak [[Van der Waals force]]s. 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 [[Delocalized electron|π-cloud]], graphite conducts [[electricity]], but only in the plane of each [[covalent bond|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 temperature. 

[[Image:Eight Allotropes of Carbon.jpg|thumb|350px|right|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 atoms. Diamond has the same [[cubic crystal system|cubic structure]] as [[silicon]] and [[germanium]] and, thanks to the strength of the carbon-carbon [[chemical bond|bonds]] 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 graphite.<ref name="therm prop"/> But 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, a form similar to diamond but forming a hexagonal [[crystal]] lattice.<ref name="lonsdaletite"/>
 
*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, [[carbon nanotube|buckytube]]s and nanobuds) have not yet been fully analyzed and represents an intense are of research in nanomaterials. The name ''"fullerene"'' is given after Richard Buckminster Fuller, developer of some 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 structure C<sub>60</sub> buckminsterfullerene).<ref name="buckyballs"/> Carbon nanotubes are structurally similar to buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder.<ref name="nanotubes"/><ref name="nanotubes2"/> Nanobuds were first published 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 structure.<ref name="nanobuds"/>

*Of the other discovered allotropes, aggregated diamond nanorods have been synthesised in 2005 and are believed to be the hardest substance known yet.<ref>{{cite web |url=http://www.esrf.eu/NewsAndEvents/Spotlight/spotlight25nanorods/ |title=Aggregated Diamond Nanorods, the Densest and Least Compressible Form of Carbon |accessdate=2007-12-21}}</ref> 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/m³.<ref>{{cite web |url=http://newton.ex.ac.uk/aip/physnews.678.html#1 |title=Carbon Nanofoam is the World's First Pure Carbon Magnet |accessdate=2007-12-21}}</ref> Similarly, glassy carbon contains a high proportion of closed porosity.<ref name="glassy carbon"/> But unlike normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random arrangement. Linear acetylenic carbon<ref name=LAC/> has the chemical structure<ref>Carbyne and Carbynoid Structures Series: Physics and Chemistry of Materials with Low-Dimensional Structures, Vol.  21 Heimann, R.B.; Evsyukov, S.E.; Kavan, L. (Eds.) 1999, 452 p., Hardcover ISBN 0-7923-5323-4</ref> -(C:::C)<sub>n</sub>- .Carbon in this modification is linear with ''sp'' [[orbital hybridisation]], and is a [[polymer]] with alternating single and triple bonds. 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.<ref>Harder than Diamond: Determining the Cross-Sectional Area and Young's Modulus of Molecular Rods, Lior Itzhaki et al, Angew. Chem. Int. Ed. 2005, 44, 7432-7435.</ref>

<!-- [[Carbon fiber]]s are similar to graphite. Under special treatment (stretching of organic fibers and carbonization) it is possible to arrange the carbon planes in direction of the fiber. Perpendicular to the fiber axis there is no orientation of the carbon planes. The result are fibers with a higher [[specific strength]] than steel. -->

=== Occurrence ===
[[Image:GraphiteOreUSGOV.jpg|thumb|200px|left|Graphite ore]]
[[Image:Rough diamond.jpg|left|thumb|200px|Raw diamond crystal.]]

Carbon is the [[Abundance of the chemical elements|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 disk. Microscopic diamonds may also be formed by the intense pressure and high temperature at the sites of meteorite impacts.<ref>{{cite book |author=Mark |last=Mark |year=1987 |title=Meteorite Craters |publisher=University of Arizona Press}}</ref>

[[Image:TIC oceans.jpg|thumb|right|200px|"Present day" (1990s) sea surface dissolved inorganic carbon concentration (from the Global Ocean Data Analysis Project climatology)]]

In combination with [[oxygen]] in [[carbon dioxide]], carbon is found in the Earth's atmosphere (in quantities of approximately 810 gigatonnes) and dissolved in all water bodies (approximately 36000 gigatonnes). Around 1900 gigatonnes are present in the biosphere. [[Hydrocarbons]] (such as coal, [[petroleum]], and [[natural gas]]) contain carbon as well &mdash; coal "reserves" (not "resources") amount to around 900 gigatonnes, and oil reserves around 150 gigatonnes. With smaller amounts of [[calcium]], [[magnesium]], and [[iron]], carbon is a major component of very large masses [[carbonate]] rock (limestone, dolomite, marble etc.).

Coal is a significant commercial source of mineral carbon; [[anthracite]] containing 92-98% carbon and the largest source (4000 Gt, or 80% of coal, gas and oil reserves) of carbon in a form suitable for use as fuel.<ref>{{cite journal |author=James Kasting |last=Kasting |first=James |year=1998 |title=The Carbon Cycle, Climate, and the Long-Term Effects of Fossil Fuel Burning |journal=Consequences: The Nature and Implication of Environmental Change |volume=4 |number=1}}</ref>

Graphite is found in large quantities in New York and Texas in the United States, Russia, Mexico, Greenland, and India.

Natural diamonds occur in the mineral 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 Leone. There are also deposits in Arkansas, Canada, the Russian Arctic, Brazil and in Northern and Western Australia.

Carbon is also found in abundance in the Sun, stars, comets, and atmospheres of most planets. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. About 30% of all industrial diamonds used in the U.S. are now made synthetically.

According to studies from the Massachusetts Institute of Technology, an estimate of the global carbon budget is:

{| class="wikitable" style="font-size: 90%; float: right; margin-left: 1em;"
|-
! colspan="2" style="text-align: center;" |Biosphere, oceans, atmosphere
|-
| colspan="2" style="text-align: center;" |0.45 x 10<sup>18</sup> [[kilogram]]s (3.7 x 10<sup>18</sup> [[mole (unit)|moles]])
|-
! colspan="2" style="text-align: center;" |Crust
|-
! Organic carbon
|13.2 x 10<sup>18</sup> kg
|-
!Carbonates
|62.4 x 10<sup>18</sup> kg
|-
! colspan="2" style="text-align: center;" |Mantle
|-
| colspan="2" style="text-align: center;" |1200 x 10<sup>18</sup> kg
|}

Carbon-14 is formed in upper layers of the troposphere and the stratosphere, at altitudes of 9&ndash;15 km, by a reaction that is precipitated by cosmic rays. Thermal neutrons are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton.

=== Isotopes ===
[[Isotopes]] of carbon are [[atomic nucleus|atomic nuclei]] that contain six [[proton]]s plus a number of [[neutron]]s (varying from 2 to 16). Carbon has two stable, naturally occurring [[isotope]]s.<ref name="isotopes"/> The isotope [[carbon-12]] (<sup>12</sup>C) forms 98.93% of the carbon on Earth, while [[carbon-13]] (<sup>13</sup>C) forms the remaining 1.07%.<ref name="isotopes"/> The concentration of <sup>12</sup>C is further increased in biological materials because biochemical reactions discriminate against <sup>13</sup>C.<ref>{{cite journal|last =Gannes|first =Leonard Z.|coauthors =Martínez del Rio, Carlos; Koch, Paul|title =Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology|journal =Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology|volume =119|issue =3|pages =725&ndash;737|publisher =Elsevier Science|location =New York|date= March 1998|url =|doi =10.1016/S1095-6433(98)01016-2|accessdate =  }}</ref> In 1961 the [[International Union of Pure and Applied Chemistry]] (IUPAC) adopted the isotope [[carbon-12]] as the basis for [[atomic weight]]s.<ref>{{cite web |url=http://www.bipm.org/en/si/base_units/ |title=Official SI Unit definitions |accessdate=2007-12-21}}</ref> Identification of carbon in [[NMR]] experiments is done with the isotope <sup>13</sup>C.

[[Carbon-14]] (<sup>14</sup>C) is a naturally occurring [[radioisotope]] which occurs in trace amounts on Earth of up to 1 part per trillion (0.0000000001%), mostly confined to the atmosphere and superficial deposits, particularly of peat and other organic materials.<ref>{{cite web|last=Brown | first=Tom | date=[[March 1]], [[2006]]|url=http://www.llnl.gov/str/March06/Brown.html|title=Carbon Goes Full Circle in the Amazon|publisher=Lawrence Livermore National Laboratory|accessdate=2007-11-25}}</ref> This isotope decays by 0.158 MeV [[beta decay|β<sup>-</sup> emission]]. Because of its relatively short [[half-life]] of 5730 years, <sup>14</sup>C is virtually absent in ancient rocks, but is created in the upper atmosphere (lower stratosphere and upper troposphere) by interaction of [[nitrogen]] with cosmic rays.<ref>{{cite book |author=Bowman, S. |first=S. |last=Bowman |year=1990 |title=Interpreting the past: Radiocarbon dating |publisher=British Museum Press |isbn=0-7141-2047-2}}</ref> The abundance of <sup>14</sup>C 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, discovered in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000 years.<ref>{{cite book |author=Libby WF |last=Libby |first=WF |year=1952 |title=Radiocarbon dating |publisher=Chicago University Press and references therein}}</ref><ref>{{cite web
|last=Westgren | first=A. | year=1960
|url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1960/press.html
|title=The Nobel Prize in Chemistry 1960
|publisher=Nobel Foundation | accessdate=2007-11-25 }}</ref> 

There are 15 known isotopes of carbon and the shortest-lived of these is <sup>8</sup>C which decays through [[proton emission]] and [[alpha decay]] and has a half-life of 1.98739x10<sup>-21</sup> s.<ref>{{cite web |url=http://barwinski.net/isotopes/query_select.php |title=Use query for carbon-8 |accessdate=2007-12-21}}</ref> The exotic <sup>19</sup>C exhibits a nuclear halo, which means its [[radius]] is appreciably larger than would be expected if the [[nucleus]] was a sphere of constant [[density]].<ref>{{cite web |url=http://www.sciencemag.org/cgi/content/full/286/5437/28?ck=nck |title=Beaming Into the Dark Corners of the Nuclear Kitchen |accessdate=2007-12-21}}</ref>

=== Formation in stars ===
Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of [[alpha particle]]s ([[helium]] nuclei) within the core of a giant or supergiant star. This happens in conditions of temperature 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 process. 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- and third-generation star systems which have planets accreted from such dust. The Solar System is one such third-generation star system.

One of the fusion mechanisms powering stars is the [[carbon-nitrogen cycle]].

Rotational transitions of various isotopic forms of carbon monoxide (e.g. <sup>12</sup>CO, <sup>13</sup>CO, and C<sup>18</sup>O) are detectable in the submillimeter regime, and are used in the study of newly forming stars in molecular clouds.

=== Carbon cycle ===
{{main|Carbon cycle}}
[[Image:Carbon cycle-cute diagram.jpeg|thumb|300px||Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions of tons ("GtC" stands for gigatons of carbon; figures are circa 2004). The purple numbers indicate how much carbon moves between reservoirs each year. 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 cycle]]. 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 oceans; dead plant or animal matter may become [[petroleum]] or coal, which can burn with the release of carbon, should bacteria not consume it.

== Compounds ==
=== Inorganic compounds ===

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). Among these are the simple oxides of carbon. The most prominent oxide is [[carbon dioxide]] ({{chem|C||O|2}}). This was once the principal constituent of the paleoatmosphere, but is a minor component of the Earth's atmosphere today.<ref>{{citejournal|author=JS Levine, TR Augustsson and M Natarajan |year=1982 |title=The prebiological paleoatmosphere: stability and composition |journal=Origins of Life and Evolution of Biospheres |volume= 12 |number=3 |page=245-259}}</ref> Dissolved in [[water (molecule)|water]], it forms [[carbonic acid]] ({{chem|H|2|C||O|3}}), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized [[carbonate]] [[ion]]s are produced. Some important minerals are carbonates, notably calcite. [[Carbon disulfide]] ({{chem|C||S|2}}) 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 molecule|polar]], resulting in a tendency to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower binding affinity.<ref>{{cite journal |author=Haldane J. |year=1895 |title=The action of carbonic oxide on man |journal=Journal of Physiology |volume=18 |page=430-462}}</ref><ref>{{cite journal |co-authors=Gorman D, Drewry A, Huang YL & Sames C |year=2003 |title=The clinical toxicology of carbon monoxide |journal=Toxicology |number=187 |page=25-38}}</ref> [[Cyanide]] (CN<sup>–</sup>), has a similar structure, but behaves much like a [[halide]] ion ([[pseudohalogen]]). For example it can form the nitride [[cyanogen]] molecule ((CN)<sub>2</sub>), similar to diatomic halides.  Other uncommon oxides are carbon suboxide ({{chem|C|3|O|2}}),<ref>{{citeweb|title= Compounds of carbon: carbon suboxide|url=http://www.webelements.com/webelements/compounds/text/C/C3O2-504643.html|accessdate=2007-12-03}}</ref> the unstable [[dicarbon monoxide]] (C<sub>2</sub>O),<ref>{{citejournal|author= Bayes K.|title=Photolysis of Carbon Suboxide|journal=[[Journal of the American Chemical Society]]|volume=83|year=1961|pages=3712-3713|doi=10.1021/ja01478a033}}</ref><ref>{{citejournal|author=Anderson D. J.|coauthor=Rosenfeld R. N.|title=Photodissociation of Carbon Suboxide|journal=[[Journal of Chemical Physics]]|volume=94|year=1991|pages=7852-7867|doi=10.1063/1.460121}}</ref> and even [[carbon trioxide]] (CO<sub>3</sub>).<ref>{{citejournal|title=A theoretical study of the structure and properties of carbon trioxide|author=Sabin, J. R.|coauthor=Kim, H.|journal=[[Chemical Physics Letters]]|volume=11|issue=5|pages=593-597|date=11/1971}}</ref><ref>{{citejournal|title=Carbon Trioxide: Its Production, Infrared Spectrum, and Structure Studied in a Matrix of Solid CO<sub>2</sub>|journal=The [[Journal of Chemical Physics]]|year=1966|volume=45|issue=12|pages=4469-4481|doi=10.1063/1.1727526|author=Moll N. G., Clutter D. R., Thompson W. E.}}</ref> 

With reactive [[metal]]s, such as [[tungsten]], carbon forms either carbides (C<sup>4–</sup>), or acetylides (C<sub>2</sub><sup>2–</sup>) to form alloys with high melting points. These anions are also associated with [[methane]] and [[acetylene]], both very weak [[acid]]s. With an electronegativity of 2.5,<ref>{{cite book |author= L. Pauling |title= The Nature of the Chemical Bond |edition= 3<sup>rd</sup> ed. |publisher= Cornell University Press |location= Ithaca, NY |year= 1960 |pages= 93 }}</ref> carbon prefers to form [[covalent bond]]s. A few carbides are covalent lattices, like carborundum (SiC), which resembles diamond.

=== Organic compounds ===
{{main|Organic compound}}
Carbon has the ability to form very long chains with 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).

The simplest form of an organic molecule is the [[hydrocarbon]]&mdash;a large family of [[organic molecule]]s that are composed of [[hydrogen]] atoms bonded to a chain of carbon atoms. Chain length, side chains and [[functional group]]s all affect the properties of organic molecules. By [[IUPAC]]'s definition, all the other organic compounds are functionalized compounds of hydrocarbons.

[[Image:Plastic household items.jpg|thumb|200px|left|Carbon is the basis for all plastic materials that are used in common household items.]]

Carbon occurs in all [[organic material|organic]] [[life]] and is the basis of [[organic chemistry]]. When united with [[hydrogen]], it forms various flammable compounds called [[hydrocarbon]]s which are important to industry as chemical feedstock for the manufacture of [[plastic]]s, [[petrochemicals]] and as fossil fuels.

When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including [[sugar]]s, [[cellulose]]s, [[lignan]]s, [[chitin]]s, [[alcohol]]s, [[fat]]s, and aromatic [[ester]]s, [[carotenoids]] and terpenes. With [[nitrogen]] it forms [[alkaloid]]s, and with the addition of sulfur also it forms [[antibiotic]]s, [[amino acid]]s and [[protein]]s. With the addition of phosphorus to these other elements, it forms [[DNA]] and [[RNA]], the chemical codes of life, and [[adenosine triphosphate]] (ATP), the most important energy-transfer molecules in all living cells.

== History and etymology ==

The English name ''carbon'' comes from the Latin ''carbo'' for coal and charcoal,<ref>Shorter Oxford English Dictionary, Oxford University Press</ref> and hence comes French ''charbon'', meaning charcoal. In German, Dutch and Danish, the names for carbon are ''Kohlenstoff'', ''koolstof'' and ''kulstof'' respectively, all literally meaning coal-substance.

[[Image:Carl Wilhelm Scheele from Familj-Journalen1874.png|thumb|100px|left|Carl Wilhelm Scheele]]
[[Image:Antoine lavoisier.jpg|thumb|100px|left|Antoine Lavoisier in his youth]]
Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizations. Diamonds were known probably as early as 2500 BCE in China, while carbon in the forms 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.<ref name=ancient_China>{{cite news | url = http://news.bbc.co.uk/2/hi/science/nature/4555235.stm | title = Chinese made first use of diamond | publisher = BBC News | date=  17 May 2005 | accessdate = 2007-03-21}}</ref><ref>{{cite web |url=http://www.vanderkrogt.net/elements/elem/c.html |title=Carbonium/Carbon at Elementymology & Elements Multidict |author= Peter van der Krogt |last=van der Krogt |first=Peter |accessdate=2007-12-21}}</ref>

In 1722, René A. F. de Réaumur demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon.<ref>{{cite book |author=R-A Ferchault de Réaumur |last=Ferchault de Réaumur |first=R-A |year=1722 |title=L'art de convertir le fer forgé en acier, et l'art d'adoucir le fer fondu, ou de faire des ouvrages de fer fondu aussi finis que le fer forgé (English translation from 1956) |location=Paris, Chicago}}</ref> In 1772, [[Antoine Lavoisier]] showed that diamonds are a form of carbon, when he burned samples of carbon and diamond then showed that neither produced any water and that both released the same amount of [[carbon dioxide]] per [[gram]].
[[Carl Wilhelm Scheele]] showed that graphite, which had been thought of as a form of [[lead]], was instead a type of carbon.<ref>{{citeweb|author=Senese, Fred|url=http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/discovery-of-carbon.shtml | title=Who discovered carbon? | publisher=Frostburg State University |accessdate=2007-11-24}}</ref> In 1786, the French scientists Claude Louis Berthollet, Gaspard Monge and C. A. Vandermonde then showed that this substance was carbon.<ref>{{citebook|author=Federico Giolitti|year=1914
|title=The Cementation of Iron and Steel|publisher=McGraw-Hill Book Company, inc.}}</ref> In their publication they proposed the name carbone (Latin carbonum) for this element. Antoine Lavoisier listed carbon as an [[chemical element|element]] in his 1789 textbook.<ref>{{citeweb|author=Senese,Fred |date=September 9, 2009|url=http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/discovery-of-carbon.shtml|title=Who discovered carbon?|publisher=Frostburg State University|accessdate=2007-11-24 }}</ref>

A new [[allotrope]] of carbon, fullerene, that was discovered in 1985<ref>{{citejournal|journal=Nature|volume=318|pages=162 - 163|year=1985|doi=10.1038/318162a0|title=C<sup>60</sup>: Buckminsterfullerene|author=H. W. Kroto, J. R. Heath, S. C. O'Brien, R. F. Curl and  R. E. Smalley}}</ref>  includes nanostructured forms such as buckyballs and nanotubes.<ref name="buckyballs">{{citeweb|url=http://www.ch.ic.ac.uk/local/projects/unwin/Fullerenes.html|title=Fullerenes(An Overview)|author=Peter Unwin|accessdate=2007-12-08}}</ref> Their discoverers received the Noble Prize in Chemistry in 1996.<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/chemistry/laureates/1996/index.html |title=The Nobel Prize in Chemistry 1996 "for their discovery of fullerenes" |accessdate=2007-12-21}}</ref> 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.<ref name="glassy carbon">{{cite journal |author=PJF Harris |last=Harris |first=PJF |year=2004 |title=Fullerene-related structure of commercial glassy carbons |journal=Philosophical Magazine, 84, 3159–3167}}</ref>
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=== Applications ===
[[Image:Mechanical pencil lead spilling out 051907.jpg|thumb|right|200px|Pencil lead for mechanical pencils are made of graphite.]]
[[Image:Charcoal sticks 051907.jpg|left|thumb|200px|Sticks of vine and compressed charcoal.]]
[[Image:Kohlenstofffasermatte.jpg|thumb|left|200px|A cloth of woven carbon filaments]] 
[[Image:SiC p1390066.jpg|thumb|right|Silicon carbide single crystal]]
[[Image:C60-Fulleren-kristallin.JPG|thumb|left|200px|The ''C''<sub>60</sub> fullerene in crystalline form]]
[[Image:Tungsten carbide.jpg|thumb|right|200px|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 others, gasoline and kerosene, through a [[distillation]] process, in refineries. [[Cellulose]] is natural carbon-containing polymer produced by plants in the form of [[cellulose]], [[cotton]], linen, [[hemp]].  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 chain. 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 [[clay]]s to form the 'lead' used in pencils used for writing and drawing. It is also used as a [[lubricant]] and a pigment, as a moulding material in glass manufacture, 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 drilling, 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 substances. 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 steel.

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 masks, water purification and kitchen extractor hoods and in medicine to absorb toxins, poisons, or gases from the [[gastrointestinal tract|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 titanium, 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 metal.

== Production ==
===Graphite Production===
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.<ref>[http://minerals.usgs.gov/minerals/pubs/commodity/graphite/myb1-2006-graph.pdf USGS Minerals Yearbook: Graphite, 2006]</ref> Graphite deposits are of metamorphic origin, found in association with quartz, mica and  feldspars in schists, gneisses and metamorphosed sandstones and limestone as lenses or veins, sometimes of a [[metre]] or more in thickness. Deposits of graphite in Borrowdale, Cumberland, England were at first of sufficient size and purity that, until the 1800s, pencils were made simply by sawing blocks of natural graphite into strips before encasing the strips in wood. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.

== Precautions ==
Pure carbon has extremely low toxicity 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 if it gets into body tissues it is likely to remain there indefinitely. [[Carbon black]] was probably one of the first pigments to be used for [[tattoo]]ing, and Ötzi the Iceman was found to have carbon tattoos that survived during his life and for 5200 years after his death.<ref>L. Dorfer ''et al'', 1998. 5200-year old [[acupuncture]] in Central Europe? Science 282, 242-243</ref> 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 pneumoconiosis]]. 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.<ref>Donaldson K, Stone V, Clouter A, Renwick L, MacNee W (2001) Ultrafine particles. Occupational and  Environmental Medicine 58, 211-216</ref> 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 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 hundred of millions of years in the absence of oxygen, may spontaneously combust when exposed to air, for example in coal mine waste tips.
 
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 poisoning|cyanide]] (CN<sup>-</sup>) and [[Carbon monoxide poisoning|carbon monoxide]]; and such essentials to life as [[glucose]] and [[protein]].

== See also ==
<div style="-moz-column-count:2; column-count:2;">
* [[Organic chemistry]]
</div>

== References ==
{{reflist|2}}
* ''[http://lbruno.home.cern.ch/lbruno/documents/Bibliography/LHC_Note_78.pdf On Graphite Transformations at High Temperature and Pressure Induced by Absorption of the LHC Beam]'', J.M. Zazula, 1997

== External links ==
* [http://www.britannica.com/eb/article-80956/carbon-group-element Carbon on Britannica]
* [http://www.webelements.com/webelements/elements/text/C/index.html WebElements.com &ndash; Carbon]
* [http://www.chemicool.com/elements/carbon.html Chemicool.com &ndash; Carbon]
* [http://education.jlab.org/itselemental/ele006.html It's Elemental &ndash; Carbon]
* [http://invsee.asu.edu/nmodules/Carbonmod/everywhere.html Extensive Carbon page at asu.edu]
* [http://electrochem.cwru.edu/ed/encycl/art-c01-carbon.htm Electrochemical uses of carbon]
* [http://www.compchemwiki.org/index.php?title=Carbon Computational Chemistry Wiki]
* [http://www.forskning.no/Artikler/2006/juni/1149432180.36 Carbon - Super Stuff. Animation with sound and interactive 3D-models.]
* [http://www.bbc.co.uk/radio4/history/inourtime/inourtime_20060615.shtml BBC Radio 4 series "In Our Time", on ''Carbon, the basis of life'', 15 June 2006]
* [http://canadaconnects.ca/chemistry/1009/ Introduction to Carbon Properties geared for High School students.]

{{Compact periodic table}}

[[Category:Carbon| ]]
[[Category:Carbonate minerals]]
[[Category:Chemical elements]]
[[Category:Organic minerals]]

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[[af:Koolstof]]
[[als:Kohlenstoff]]
[[ar:كربون]]
[[ast:Carbonu]]
[[az:Karbon]]
[[bn:কার্বন]]
[[zh-min-nan:C (goân-sò͘)]]
[[be:Вуглярод]]
[[bg:Въглерод]]
[[ca:Carboni]]
[[cs:Uhlík]]
[[co:Carboniu]]
[[cy:Carbon]]
[[da:Carbon]]
[[de:Kohlenstoff]]
[[et:Süsinik]]
[[el:Άνθρακας]]
[[es:Carbono]]
[[eo:Karbono]]
[[eu:Karbono]]
[[fa:کربن]]
[[fr:Carbone]]
[[fur:Carboni]]
[[ga:Carbón]]
[[gv:Carboan]]
[[gd:Gualan]]
[[gl:Carbono]]
[[gu:કાર્બન]]
[[ko:탄소]]
[[hy:Ածխածին]]
[[hi:कार्बन]]
[[hsb:Wuhlik]]
[[hr:Ugljik]]
[[io:Karbo]]
[[id:Karbon]]
[[ia:Carbon]]
[[is:Kolefni]]
[[it:Carbonio]]
[[he:פחמן]]
[[jv:Karbon]]
[[kn:ಇಂಗಾಲ]]
[[sw:Kaboni]]
[[ht:Kabòn]]
[[ku:Karbon]]
[[la:Carbonium]]
[[lv:Ogleklis]]
[[lb:Kuelestoff]]
[[lt:Anglis]]
[[li:Koolstof]]
[[ln:Kaboni]]
[[jbo:tabno]]
[[lmo:Carbòni]]
[[hu:Szén]]
[[mk:Јаглерод]]
[[ml:കാര്‍ബണ്‍]]
[[mi:Waro]]
[[mr:कार्बन]]
[[ms:Karbon]]
[[mn:Нүүрстөрөгч]]
[[nah:Tecolli]]
[[nl:Koolstof]]
[[ja:炭素]]
[[no:Karbon]]
[[nn:Karbon]]
[[nov:Karbo]]
[[oc:Carbòni]]
[[uz:Uglerod]]
[[nds:Kohlenstoff]]
[[pl:Węgiel (pierwiastek)]]
[[pt:Carbono]]
[[ksh:Kohlenstoff]]
[[ro:Carbon]]
[[qu:K'illimsayaq]]
[[ru:Углерод]]
[[sq:Karboni]]
[[scn:Carbòniu]]
[[simple:Carbon]]
[[sk:Uhlík]]
[[sl:Ogljik]]
[[sr:Угљеник]]
[[sh:Ugljenik]]
[[su:Karbon]]
[[fi:Hiili]]
[[sv:Kol]]
[[tl:Karbon]]
[[ta:கரிமம்]]
[[th:คาร์บอน]]
[[vi:Cacbon]]
[[tg:Карбон]]
[[tr:Karbon]]
[[uk:Вуглець]]
[[wa:Carbone]]
[[vls:Carboun]]
[[wuu:碳]]
[[yi:קוילנשטאף]]
[[zh-yue:碳]]
[[bat-smg:Onglis]]
[[zh:碳]]

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