Carbon - Wikipedia, The Free Encyclopedia

Carbon

Periodic table

-↑C↓Si

boron ← carbon → nitrogen

Appearance

clear (diamond) & black (graphite)

Spectral lines of Carbon

General properties

Name, symbol,

number

carbon, C, 6

Pronunciation /ˈkɑrbən/Element category nonmetal

Group, period,

block

14, 2, p

Standard atomic

weight

12.0107(8)

Electron

configuration

1s2 2s2 2p2 or [He] 2s2 2p2

Electrons per

shell

2,4 (Image)

History

Discovery A. Lavoisier[1] (1789)

Earliest use Egyptians & Sumerians[2]

(3750 BC)

Physical properties

CarbonFrom Wikipedia, the free encyclopedia

Carbon /ˈkɑrbən/ (from Latin: carbo "coal") is the chemicalelement with symbol C and atomic number 6. As a memberof group 14 on the periodic table, it is nonmetallic andtetravalent—making four electrons available to form covalentchemical 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 years.[11] Carbon is

one of the few elements known since antiquity.[12][13]

There are several allotropes of carbon of which the best

known are graphite, diamond, and amorphous carbon.[14] Thephysical properties of carbon vary widely with the allotropicform. For example, diamond is highly transparent, whilegraphite is opaque and black. Diamond is among the hardestmaterials known, while graphite is soft enough to form astreak on paper (hence its name, from the Greek word "towrite"). Diamond has a very low electrical conductivity,while graphite is a very good conductor. Under normalconditions, diamond has the highest thermal conductivity ofall known materials.

All carbon allotropes are solids under normal conditions withgraphite being the most thermodynamically stable form. Theyare chemically resistant and require high temperature to reacteven with oxygen. The most common oxidation state ofcarbon in inorganic compounds is +4, while +2 is found incarbon monoxide and other transition metal carbonylcomplexes. The largest sources of inorganic carbon arelimestones, dolomites and carbon dioxide, but significantquantities occur in organic deposits of coal, peat, oil andmethane clathrates. Carbon forms more compounds than anyother element, with almost ten million pure organiccompounds described to date, which in turn are a tinyfraction of such compounds that are theoretically possible

under standard conditions.[15]

Carbon is the 15th most abundant element in the Earth'scrust, and the fourth most abundant element in the universeby mass after hydrogen, helium, and oxygen. It is present inall known life forms, and in the human body carbon is thesecond most abundant element by mass (about 18.5%) after

oxygen.[16] This abundance, together with the uniquediversity of organic compounds and their unusual polymer-forming ability at the temperatures commonly encountered onEarth, make this element the chemical basis of all known life.

6C

Carbon - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Carbon

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Phase Solid

Density (near r.t.) amorphous:[3] 1.8–2.1 g·cm−3

Density (near r.t.) diamond: 3.515 g·cm−3

Density (near r.t.) graphite: 2.267 g·cm−3

Sublimation point 3915 K, 3642 °C, 6588 °F

Triple point 4600 K (4327°C), 10800[4][5] kPa

Heat of fusion 117 (graphite) kJ·mol−1

Molar heat

capacity

6.155 (diamond)

8.517 (graphite) J·mol−1·K−1

Atomic properties

Oxidation states 4, 3 [6], 2, 1 [7], 0, -1, -2, -3, -4[8]

Electronegativity 2.55 (Pauling scale)

Ionization

energies

(more)

1st: 1086.5 kJ·mol−1

2nd: 2352.6 kJ·mol−1

3rd: 4620.5 kJ·mol−1

Covalent radius 77(sp³), 73(sp²), 69(sp) pm

Van der Waals

radius

170 pm

Miscellanea

Crystal structure diamond

(diamond, clear)

simple hexagonal

(graphite, black)

Magnetic

ordering

diamagnetic[9]

Thermal

conductivity

900-2300 (diamond)

119-165 (graphite) W·m−1·K−1

Thermal

expansion

(25 °C) 0.8 (diamond)[10]

µm·m−1·K−1

Speed of sound

(thin rod)

(20 °C) 18350 (diamond) m·s−1

Young's modulus 1050 (diamond)[10] GPa

Shear modulus 478 (diamond)[10] GPa

Bulk modulus 442 (diamond)[10] GPa

Theoretically predicted phase diagram

of carbon

Contents

1 Characteristics1.1 Allotropes1.2 Occurrence1.3 Isotopes1.4 Formation in stars1.5 Carbon cycle

2 Compounds2.1 Organic compounds2.2 Inorganic compounds2.3 Organometallic compounds

3 History and etymology4 Production

4.1 Graphite4.2 Diamond

5 Applications5.1 Diamonds

6 Precautions7 Bonding to carbon8 See also9 References10 External links

Characteristics

The different forms orallotropes of carbon(see below) includethe hardest naturallyoccurring substance,diamond, and also oneof the softest knownsubstances, graphite.Moreover, it has anaffinity for bondingwith other smallatoms, including othercarbon atoms, and is

capable of forming multiple stable covalent bonds with suchatoms. As a result, carbon is known to form almost tenmillion different compounds; the large majority of all

chemical compounds.[15] Carbon also has the highestsublimation point of all elements. At atmospheric pressure ithas 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),[4][5] so it


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Poisson ratio 0.1 (diamond)[10]

Mohs hardness 10 (diamond)

1-2 (graphite)

CAS registry

number

7440-44-0

Most stable isotopes

Main article: Isotopes of carbon

iso NA half-life DM DE (MeV) DP

15

11C syn 20 min β+ 0.96 11B

12C 98.9% 12C is stable with 6 neutrons

13C 1.1% 13C is stable with 7 neutrons

14C trace 5730 y β- 0.15 14N

sublimates at about 3,900 K.[17][18]

Carbon sublimes in a carbon arc which has a temperature ofabout 5,800 K (5,530 °C; 9,980 °F). Thus, irrespective of itsallotropic form, carbon remains solid at higher temperaturesthan the highest melting point metals such as tungsten orrhenium. Although thermodynamically prone to oxidation,carbon resists oxidation more effectively than elements suchas iron and copper that are weaker reducing agents at roomtemperature.

Carbon compounds form the basis of all known life on Earth,and the carbon-nitrogen cycle provides some of the energyproduced by the Sun and other stars. Although it forms anextraordinary variety of compounds, most forms of carbonare comparatively unreactive under normal conditions. Atstandard temperature and pressure, it resists all but thestrongest oxidizers. It does not react with sulfuric acid,hydrochloric acid, chlorine or any alkalis. At elevatedtemperatures carbon reacts with oxygen to form carbonoxides, and will reduce such metal oxides as iron oxide to themetal. 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 reaction:

C(s) + H2O(g) → CO(g) + H2(g).

Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbidecementite 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.[19] However, the process of separating itfrom graphite will require some technological development before it is economical enough to be used in

industrial processes.[20]

The system of carbon allotropes spans a range of extremes:

Synthetic nanocrystalline diamond is the hardestmaterial known.[21]

Graphite is one of the softest materials known.

Diamond is the ultimate abrasive.Graphite is a very good lubricant, displaying

superlubricity.[22]

Diamond is an excellent electrical insulator.[23] Graphite is a conductor of electricity.[24]

Diamond is the best known naturally occurringthermal conductor

Some forms of graphite are used for thermalinsulation (i.e. firebreaks and heat shields)

Diamond is highly transparent. Graphite is opaque.


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Some allotropes of carbon: a) diamond; b) graphite;

c) lonsdaleite; d–f) fullerenes (C60, C540, C70); g)

amorphous carbon; h) carbon nanotube.

Diamond crystallizes in the cubic system. Graphite crystallizes in the hexagonal system.[25]

Amorphous carbon is completely isotropic.Carbon nanotubes are among the most anisotropicmaterials ever produced.

Allotropes

Main article: Allotropes of carbon

Atomic carbon is a very short-lived species and, therefore, carbon is stabilized in various multi-atomic structureswith different molecular configurations called allotropes. The three relatively well-known allotropes of carbonare amorphous carbon, graphite, and diamond. Once considered exotic, fullerenes are nowadays commonly

synthesized and used in research; they include buckyballs,[26][27] carbon nanotubes,[28] carbon nanobuds[29]

and nanofibers.[30][31] Several other exotic allotropes have also been discovered, such as lonsdaleite,[32] glassy

carbon,[33] carbon nanofoam[34] and linear acetylenic carbon (carbyne).[35]

The amorphous form is an assortment of carbon atoms in a non-crystalline, irregular, glassy state, which isessentially graphite but not held in a crystalline macrostructure. It is present as a powder, and is the mainconstituent of substances such as charcoal, lampblack (soot) and activated carbon. At normal pressures carbontakes 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.[36] The resulting network is 2-dimensional, and theresulting flat sheets are stacked and loosely bonded through weak van der Waals forces. This gives graphite itssoftness and its cleaving properties (the sheets slip easily past one another). Because of the delocalization of oneof the outer electrons of each atom to form a π-cloud, graphite conducts electricity, but only in the plane of eachcovalently bonded sheet. This results in a lower bulk electrical conductivity for carbon than for most metals. Thedelocalization also accounts for the energetic stability of graphite over diamond at room temperature.

At very high pressures carbon forms the more compactallotrope diamond, having nearly twice the density ofgraphite. Here, each atom is bonded tetrahedrally to fourothers, thus making a 3-dimensional network of puckeredsix-membered rings of atoms. Diamond has the same cubicstructure as silicon and germanium and because of thestrength of the carbon-carbon bonds, it is the hardestnaturally occurring substance in terms of resistance toscratching. Contrary to the popular belief that "diamondsare forever", they are in fact thermodynamically unstable

under normal conditions and transform into graphite.[14]

However, due to a high activation energy barrier, thetransition into graphite is so extremely slow at roomtemperature as to be unnoticeable. Under some conditions,carbon crystallizes as lonsdaleite. This form has a hexagonalcrystal lattice where all atoms are covalently bonded.Therefore, all properties of lonsdaleite are close to those of

diamond.[32]

Fullerenes have a graphite-like structure, but instead ofpurely hexagonal packing, they also contain pentagons (or


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Graphite ore

Raw diamond crystal.

even heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties offullerenes (split into buckyballs, buckytubes and nanobuds) have not yet been fully analyzed and represent anintense area of research in nanomaterials. The names "fullerene" and "buckyball" are given after RichardBuckminster Fuller, popularizer of geodesic domes, which resemble the structure of fullerenes. The buckyballsare fairly large molecules formed completely of carbon bonded trigonally, forming spheroids (the best-known

and simplest is the soccerball-shaped C60 buckminsterfullerene).[26] Carbon nanotubes are structurally similar to

buckyballs, except that each atom is bonded trigonally in a curved sheet that forms a hollow cylinder.[27][28]

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 structure.[29]

Of the other discovered allotropes, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consistsof a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web, in whichthe 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.[37] Similarly, glassy carbon contains a high proportion of closed porosity,[33] butcontrary to normal graphite, the graphitic layers are not stacked like pages in a book, but have a more random

arrangement. Linear acetylenic carbon[35] has the chemical structure[35] -(C:::C)n-. Carbon in this modificationis linear with sp orbital hybridization, and is a polymer with alternating single and triple bonds. This type ofcarbyne is of considerable interest to nanotechnology as its Young's modulus is forty times that of the hardest

known material – diamond.[38]

Occurrence

Carbon is the fourth most abundant chemical element in the universe bymass after hydrogen, helium, and oxygen. Carbon is abundant in the Sun,stars, comets, and in the atmospheres of most planets. Some meteoritescontain microscopic diamonds that were formed when the solar systemwas still a protoplanetary disk. Microscopic diamonds may also beformed by the intense pressure and high temperature at the sites of

meteorite impacts.[39]

In combination with oxygen in carbon dioxide, carbon is found in theEarth's atmosphere (approximately 810 gigatonnes of carbon) anddissolved in all water bodies (approximately 36,000 gigatonnes ofcarbon). Around 1,900 gigatonnes of carbon are present in the biosphere.Hydrocarbons (such as coal, petroleum, and natural gas) contain carbonas well—coal "reserves" (not "resources") amount to around900 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 gas, representing

about 540 gigatonnes of carbon.[40] (In the past, quantities ofhydrocarbons were greater. In the period from 1751 to 2008 about 347gigatonnes of carbon were released as carbon dioxide to the atmosphere

from burning of fossil fuels.[41]) Carbon is also locked up as methaneand 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 Shelf.[42]

Carbon is a major component in very large masses of carbonate rock (limestone, dolomite, marble and so on).


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"Present day" (1990s) sea surface

dissolved inorganic carbon

concentration (from the GLODAP

climatology)

Coal is the largest commercial source of mineral carbon, accounting for

4,000 gigatonnes or 80% of fossil carbon fuel.[43] It is also rich in carbon

– for example, anthracite contains 92–98%.[44]

As for individual carbon allotropes, graphite is found in large quantitiesin 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 arein Africa, notably in South Africa, Namibia, Botswana, the Republic ofthe Congo, and Sierra Leone. There are also deposits in Arkansas,Canada, the Russian Arctic, Brazil and in Northern and WesternAustralia. Diamonds are now also being recovered from the ocean flooroff the Cape of Good Hope. However, though diamonds are foundnaturally, about 30% of all industrial diamonds used in the U.S. are nowmade synthetically.

Carbon-14 is formed in upper layers of the troposphere and the stratosphere, at altitudes of 9–15 km, by a

reaction that is precipitated by cosmic rays.[45] Thermal neutrons are produced that collide with the nuclei ofnitrogen-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.[11] The isotope carbon-12 (12C) forms 98.93% of the

carbon on Earth, while carbon-13 (13C) forms the remaining 1.07%.[11] The concentration of 12C is further

increased in biological materials because biochemical reactions discriminate against 13C.[46] In 1961 theInternational Union of Pure and Applied Chemistry (IUPAC) adopted the isotope carbon-12 as the basis for

atomic weights.[47] 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 pertrillion (0.0000000001%), mostly confined to the atmosphere and superficial deposits, particularly of peat and

other organic materials.[48] 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 rays.[49] The abundance of 14C inthe 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.[50][51]

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.[52] The 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.[53]

Formation in stars

Main articles: Triple-alpha process and CNO cycle


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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 year. The sediments, as

defined in this diagram, do not include the

~70 million GtC of carbonate rock and kerogen.

Formation of the carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (heliumnuclei) within the core of a giant or supergiant star which is known as the triple-alpha process, as the products offurther nuclear fusion reactions of helium with hydrogen or another helium nucleus produce lithium-5 andberyllium-8 respectively, both of which are highly unstable and decay almost instantly back into smaller

nuclei.[54] This happens in conditions of temperatures over 100 megakelvin and helium concentration that therapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was createdduring 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.[55] In order to be available for formation of life as we know it, thiscarbon 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.[56] The SolarSystem is one such third-generation star system. Another of the fusion mechanisms powering stars is the CNOcycle, in which carbon acts as a catalyst to allow the reaction to proceed.

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

clouds.[57]

Carbon cycle

Main article: Carbon cycle

Under terrestrial conditions, conversion of one element toanother is very rare. Therefore, the amount of carbon onEarth is effectively constant. Thus, processes that usecarbon must obtain it somewhere and dispose of itsomewhere else. The paths that carbon follows in theenvironment make up the carbon cycle. For example, plantsdraw carbon dioxide out of their environment and use it tobuild biomass, as in carbon respiration or the Calvin cycle, aprocess of carbon fixation. Some of this biomass is eaten byanimals, whereas some carbon is exhaled by animals ascarbon dioxide. The carbon cycle is considerably morecomplicated than this short loop; for example, some carbondioxide is dissolved in the oceans; dead plant or animalmatter may become petroleum or coal, which can burn with

the release of carbon, should bacteria not consume it.[58][59]

Compounds

Organic compounds

Main article: Organic compound

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 ofcompounds; in fact, there are more known carbon-containing compounds than all the compounds of the otherchemical elements combined except those of hydrogen (because almost all organic compounds containhydrogen too).


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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 animals.

The simplest form of an organicmolecule is the hydrocarbon—alarge family of organicmolecules that are composed ofhydrogen atoms bonded to achain of carbon atoms. Chainlength, side chains andfunctional groups all affect theproperties of organic molecules.By IUPAC's definition, all theother organic compounds arefunctionalized compounds of

hydrocarbons.[citation needed]

Carbon occurs in all knownorganic life and is the basis of organic chemistry. Whenunited with hydrogen, it forms various hydrocarbons whichare important to industry as refrigerants, lubricants, solvents,as chemical feedstock for the manufacture of plastics andpetrochemicals and as fossil fuels.

When combined with oxygen and hydrogen, carbon canform many groups of important biological compoundsincluding sugars, lignans, chitins, alcohols, fats, andaromatic esters, carotenoids and terpenes. With nitrogen itforms alkaloids, and with the addition of sulfur also it formsantibiotics, amino acids, and rubber products. With theaddition of phosphorus to these other elements, it forms DNA and RNA, the chemical-code carriers of life, andadenosine 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 hydrogenor fluorine, are treated separately from classical organic compounds; however the definition is not rigid (seereference articles above). Among these are the simple oxides of carbon. The most prominent oxide is carbondioxide (CO2). This was once the principal constituent of the paleoatmosphere, but is a minor component of the

Earth's atmosphere today.[60] Dissolved in water, it forms carbonic acid (H2CO3), but as most compounds with

multiple single-bonded oxygens on a single carbon it is unstable.[61] 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.[62][63] Cyanide

(CN–), has a similar structure, but behaves much like a halide ion (pseudohalogen). For example it can form thenitride cyanogen molecule ((CN)2), similar to diatomic halides. Other uncommon oxides are carbon suboxide

(C3O2),[64] the unstable dicarbon monoxide (C2O),

[65][66] carbon trioxide (CO3),[67][68] cyclopentanepentone


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Antoine Lavoisier in his

youth

Carl Wilhelm Scheele

(C5O5)[69] cyclohexanehexone (C6O6),

[69] and mellitic anhydride (C12O9).

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,[70] carbon prefers to form covalent bonds. A few carbides are covalent lattices,like carborundum (SiC), which resembles diamond.

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 (for example, ferrocene); and transition metal carbenecomplexes. Many metal carbonyls exist (for example, tetracarbonylnickel); some workers consider the carbonmonoxide 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+. This

phenomenon has been attributed to the aurophilicity of the gold ligands.[71]

History and etymology

The English name carbon comes from the Latin carbo for coal and charcoal,[72]

whence also comes the French charbon, meaning charcoal. In German, Dutchand Danish, the names for carbon are Kohlenstoff, koolstof and kulstofrespectively, all literally meaning coal-substance.

Carbon was discovered in prehistory and was known in the forms of soot andcharcoal to the earliest human civilizations. Diamonds were known probably asearly as 2500 BCE in China, while carbon in the form of charcoal was madearound Roman times by the same chemistry as it is today, by heating wood in a

pyramid covered with clay to exclude air.[73][74]

In 1722, René Antoine Ferchault de Réaumurdemonstrated that iron was transformed intosteel through the absorption of some substance,

now known to be carbon.[75] In 1772, Antoine Lavoisier showed that diamondsare a form of carbon; when he burned samples of charcoal and diamond andfound that neither produced any water and that both released the same amount

of carbon dioxide per gram. In 1779,[76] Carl Wilhelm Scheele showed thatgraphite, which had been thought of as a form of lead, was instead identical withcharcoal but with a small admixture of iron, and that it gave "aerial acid" (his

name for carbon dioxide) when oxidized with nitric acid.[77] In 1786, the Frenchscientists Claude Louis Berthollet, Gaspard Monge and C. A. Vandermondeconfirmed that graphite was mostly carbon by oxidizing it in oxygen in much the


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same way Lavoisier had done with diamond.[78] Some iron again was left, which the French scientists thoughtwas necessary to the graphite structure. However, in their publication they proposed the name carbone (Latincarbonum) 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.[79]

A new allotrope of carbon, fullerene, that was discovered in 1985[80] includes nanostructured forms such as

buckyballs and nanotubes.[26] Their discoverers – Robert Curl, Harold Kroto and Richard Smalley – received

the Nobel Prize in Chemistry in 1996.[81] The resulting renewed interest in new forms lead to the discovery offurther exotic allotropes, including glassy carbon, and the realization that "amorphous carbon" is not strictly

amorphous.[33]

Production

Graphite

Main article: Graphite

Commercially viable natural deposits of graphite occur in many parts of the world, but the most importantsources economically are in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin,found in association with quartz, mica and feldspars in schists, gneisses and metamorphosed sandstones andlimestone 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 madesimply 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.[82]

There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphousgraphite is the lowest quality and most abundant. Contrary to science, in industry "amorphous" refers to verysmall crystal size rather than complete lack of crystal structure. Amorphous is used for lower value graphiteproducts 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 asseparate plates that crystallized in metamorphic rock. Flake graphite can be four times the price of amorphous.Good quality flakes can be processed into expandable graphite for many uses, such as flame retardants. Theforemost deposits are found in Austria, Brazil, Canada, China, Germany and Madagascar. Vein or lump graphiteis 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 Lanka.[82]

According to the USGS, world production of natural graphite was 1.1 million tonnes in 2010, to which Chinacontributed 800,00 t, India 130,000 t, Brazil 76,000 t, North Korea 30,000 t and Canada 25,000 t. No naturalgraphite was reported mined in the United States, but 118,000 t of synthetic graphite with an estimated value of

$998 million was produced in 2009.[82]

Diamond

Main article: Diamond

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


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Diamond output in 2005

Pencil leads for mechanical pencils are

made of graphite (often mixed with a

Sticks of vine and compressed

charcoal.

Only a very small fraction of the diamond ore consists of actualdiamonds. The ore is crushed, during which care has to be taken in orderto prevent larger diamonds from being destroyed in this process andsubsequently the particles are sorted by density. Today, diamonds arelocated in the diamond-rich density fraction with the help of X-rayfluorescence, after which the final sorting steps are done by hand.Before the use of X-rays became commonplace, the separation was donewith grease belts; diamonds have a stronger tendency to stick to grease

than the other minerals in the ore.[83]

Historically diamonds were known to be found only in alluvial deposits in southern India.[84] India led the world

in diamond production from the time of their discovery in approximately the 9th century BCE[85] to themid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18thcentury and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in

1725.[86]

Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after thediscovery 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.[87] Interestingly 20% of that amount has been minedin the last 5 years alone and during the last ten years 9 new mines have started production while 4 more arewaiting to be opened soon. Most of these mines are located in Canada, Zimbabwe, Angola, and one in

Russia.[87]

In the United States, diamonds have been found in Arkansas, Colorado and Montana.[88][89] In 2004, a startling

discovery of a microscopic diamond in the United States[90] led to the January 2008 bulk-sampling of kimberlite

pipes in a remote part of Montana.[91]

Today, most commercially viable diamond deposits are in Russia, Botswana, Australia and the Democratic

Republic of Congo.[92] In 2005, Russia produced almost one-fifth of the global diamond output, reports theBritish 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 1990s.[88] There are also commercial deposits beingactively mined in the Northwest Territories of Canada, Siberia (mostly in Yakutia territory; for example, Mirpipe and Udachnaya pipe), Brazil, and in Northern and Western Australia.

Applications

Carbon is essential to all knownliving systems, and without it lifeas we know it could not exist (seealternative biochemistry). Themajor economic use of carbonother than food and wood is inthe form of hydrocarbons, mostnotably the fossil fuel methanegas and crude oil (petroleum).Crude oil is used by thepetrochemical industry toproduce, amongst other things,


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clay or synthetic binder).

A cloth of woven carbon filaments

Silicon carbide single crystal

The C60 fullerene in crystalline form

Tungsten carbide milling bits

gasoline and kerosene, through adistillation process, in refineries.Cellulose is a natural, carbon-containing polymer produced byplants in the form of cotton,linen, and hemp. Cellulose ismainly used for maintainingstructure in plants. Commerciallyvaluable carbon polymers ofanimal origin include wool,cashmere and silk. Plastics aremade from synthetic carbonpolymers, often with oxygen andnitrogen atoms included atregular intervals in the mainpolymer chain. The raw materialsfor many of these syntheticsubstances come from crude oil.

The uses of carbon and itscompounds are extremely varied.It can form alloys with iron, ofwhich the most common iscarbon steel. Graphite is combined with clays to form the 'lead' used inpencils used for writing and drawing. It is also used as a lubricant and apigment, as a molding material in glass manufacture, in electrodes for dry

batteries and in electroplating and electroforming, in brushes for electric motors and as a neutron moderator innuclear 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 injewelry, 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 isused to reinforce plastics to form advanced, lightweight composite materials. Carbon fiber is made by pyrolysisof extruded and stretched filaments of polyacrylonitrile (PAN) and other organic substances. Thecrystallographic structure and mechanical properties of the fiber depend on the type of starting material, and onthe subsequent processing. Carbon fibers made from PAN have structure resembling narrow filaments ofgraphite, but thermal processing may re-order the structure into a continuous rolled sheet. The result is fibers

with higher specific tensile strength than steel.[93]

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 productssuch as tyres and in plastic compounds. Activated charcoal is used as an absorbent and adsorbent in filtermaterial in applications as diverse as gas masks, water purification and kitchen extractor hoods and in medicineto absorb toxins, poisons, or gases from the digestive system. Carbon is used in chemical reduction at hightemperatures. Coke is used to reduce iron ore into iron. Case hardening of steel is achieved by heating finishedsteel components in carbon powder. Carbides of silicon, tungsten, boron and titanium, are among the hardestknown materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most ofthe materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interiorsurfaces in the built environment other than glass, stone and metal.


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Worker at carbon black plant

in Sunray, Texas (photo by

John Vachon, 1942)

Diamonds

The diamond industry can be broadly separated into two basically distinct categories: one dealing withgem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamondsexists, 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 donot trade as a commodity: there is a substantial mark-up in the sale of diamonds, and there is not a very activemarket for resale of diamonds.

The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrialdiamonds are valued mostly for their hardness and heat conductivity, making many of the gemologicalcharacteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mineddiamonds (equal to about 100 million carats or 20 tonnes annually), unsuitable for use as gemstones and known

as bort, are destined for industrial use.[94] In addition to mined diamonds, synthetic diamonds found industrialapplications almost immediately after their invention in the 1950s; another 3 billion carats (600 tonnes) of

synthetic diamond is produced annually for industrial use.[95] The dominant industrial use of diamond is incutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require largediamonds; 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

applications.[96] 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.[97][98]

With the continuing advances being made in the production of synthetic diamonds, future applications arebeginning 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 electronics.[99]

Precautions

Pure carbon has extremely low toxicity to humans and can be handled and eveningested safely in the form of graphite or charcoal. It is resistant to dissolution orchemical 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 thereindefinitely. Carbon black was probably one of the first pigments to be used fortattooing, and Ötzi the Iceman was found to have carbon tattoos that survived

during his life and for 5200 years after his death.[100] However, inhalation ofcoal dust or soot (carbon black) in large quantities can be dangerous, irritatinglung tissues and causing the congestive lung disease coalworker'spneumoconiosis. Similarly, diamond dust used as an abrasive can do harm ifingested or inhaled. Microparticles of carbon are produced in diesel engine

exhaust fumes, and may accumulate in the lungs.[101] In these examples, theharmful effects may result from contamination of the carbon particles, withorganic chemicals or heavy metals for example, rather than from the carbonitself.

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 Drosophila.[102]

Carbon may also burn vigorously and brightly in the presence of air at high temperatures, as in the Windscale


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fire, which was caused by sudden release of stored Wigner energy in the graphite core. Large accumulations ofcoal, which have remained inert for hundreds of millions of years in the absence of oxygen, may spontaneouslycombust 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 (CN−) and carbon monoxide; and such essentials to life asglucose and protein.

Bonding to carbon

CH He

CLi CBe CB CC CN CO CF Ne

CNa CMg CAl CSi CP CS CCl Ar

CK CCa CSc CTi CV CCr CMn CFe CCo CNi CCu CZn CGa CGe CAs CSe CBr CKr

CRb CSr CY CZr CNb CMo CTc CRu CRh CPd CAg CCd CIn CSn CSb CTe CI CXe

CCs CBa CHf CTa CW CRe COs CIr CPt CAu CHg CTl CPb CBi CPo CAt Rn

Fr CRa Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Fl Uup Lv Uus Uuo

↓

CLa CCe CPr CNd CPm CSm CEu CGd CTb CDy CHo CEr CTm CYb CLu

Ac CTh CPa CU CNp CPu CAm CCm CBk Cf CEs Fm Md No Lr

Chemical bonds to carbon

Core organic chemistryMany uses inchemistry

Academic research, but nowidespread use

Bond unknown / notassessed

See also

Carbon chauvinismCarbon footprint

Low-carbon economyTimeline of carbon

nanotubes

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External links

Carbon (http://www.bbc.co.uk/programmes/p003c1cj) on In Our Time at the BBC. (listen now(http://www.bbc.co.uk/iplayer/console/p003c1cj/In_Our_Time_Carbon) )The Periodic Table of Videos video of Carbon (http://www.youtube.com/?v=wmC8Dg4n-ZA) at YouTubeCarbon on Britannica (http://www.britannica.com/eb/article-80956/carbon-group-element)Extensive Carbon page at asu.edu (http://invsee.asu.edu/nmodules/Carbonmod/everywhere.html)Electrochemical uses of carbon (http://electrochem.cwru.edu/ed/encycl/art-c01-carbon.htm)Carbon – Super Stuff. Animation with sound and interactive 3D-models. (http://www.forskning.no/Artikler/2006/juni/1149432180.36)

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