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chemical element


chemical element
Alternative Title: C


Element Properties
atomic number6
atomic weight12.0096 to 12.0116
melting point3,550 °C (6,420 °F)
boiling point4,827 °C (8,721 °F)
diamond3.52 g/cm3
graphite2.25 g/cm3
amorphous1.9 g/cm3
oxidation states+2, +3, +4
electron configuration1s22s22p2

Properties and uses

On a weight basis, carbon is 19th in order of elemental abundance in Earth’s crust, and there are estimated to be 3.5 times as many carbon atoms as silicon atoms in the universe. Only hydrogen, helium, oxygen, neon, and nitrogen are atomically more abundant in the cosmos than carbon. Carbon is the cosmic product of the “burning” of helium, in which three helium nuclei, atomic number 4, fuse to produce a carbon nucleus, atomic number 12.




Elemental carbon exists in several forms, each of which has its own physical characteristics. Two of its well-defined forms, diamond and graphite, are crystalline in structure, but they differ in physical properties because the arrangements of the atoms in their structures are dissimilar. A third form, called fullerene, consists of a variety of molecules composed entirely of carbon. Spheroidal, closed-cage fullerenes are called buckerminsterfullerenes, or “buckyballs,” and cylindrical fullerenes are called nanotubes. A fourth form, called Q-carbon, is crystalline and magnetic. Yet another form, called amorphous carbon, has no crystalline structure. Other forms—such as carbon black, charcoal, lampblack, coal, and coke—are sometimes called amorphous, but X-ray examination has revealed that these substances do possess a low degree of crystallinity. Diamond and graphite occur naturally on Earth, and they also can be produced synthetically; they are chemically inert but do combine with oxygen at high temperatures, just as amorphous carbon does. Fullerene was serendipitously discovered in 1985 as a synthetic product in the course of laboratory experiments to simulate the chemistry in the atmosphere of giant stars. It was later found to occur naturally in tiny amounts on Earth and in meteorites. Q-carbon is also synthetic, but scientists have speculated that it could form within the hot environments of some planetary cores.


Pure diamond is the hardest naturally occurring substance known and is a poor conductor of electricity. Graphite, on the other hand, is a soft slippery solid that is a good conductor of both heat and electricity. Carbon as diamond is the most expensive and brilliant of all the natural gemstones and the hardest of the naturally occurring abrasives. Graphite is used as a lubricant. In microcrystalline and nearly amorphous form, it is used as a black pigment, as an adsorbent, as a fuel, as a filler for rubber, and, mixed with clay, as the “lead” of pencils. Because it conducts electricity but does not melt, graphite is also used for electrodes in electric furnaces and dry cells as well as for making crucibles in which metals are melted. Molecules of fullerene show promise in a range of applications, including high-tensile-strength materials, unique electronic and energy-storage devices, and safe encapsulation of flammable gases, such as hydrogen. Q-carbon, which is created by rapidly cooling a sample of elemental carbon whose temperature has been raised to 4,000 K (3,727 °C [6,740 °F]), is harder than diamond, and it can be used to manufacture diamond structures (such as diamond films and microneedles) within its matrix. Elemental carbon is nontoxic.

Each of the “amorphous” forms of carbon has its own specific character, and, hence, each has its own particular applications. All are products of oxidation and other forms of decomposition of organic compounds. Coal and coke, for example, are used extensively as fuels. Charcoal is used as an absorptive and filtering agent and as a fuel and was once widely used as an ingredient in gunpowder. (Coals are elemental carbon mixed with varying amounts of carbon compounds. Coke and charcoal are nearly pure carbon.) In addition to its uses in making inks and paints, carbon black is added to the rubber used in tires to improve its wearing qualities. Bone black, or animal charcoal, can adsorb gases and colouring matter from many other materials.


Production of elemental carbon

Until 1955 all diamonds were obtained from natural deposits, most significant in southern Africa but occurring also in Brazil, Venezuela, Guyana, and Siberia. The single known source in the United States, in Arkansas, has no commercial importance; nor is India, once a source of fine diamonds, a significant present-day supplier. The primary source of diamonds is a soft bluish peridotic rock called kimberlite (after the famous deposit at Kimberley, South Africa), found in volcanic structures called pipes, but many diamonds occur in alluvial deposits presumably resulting from the weathering of primary sources. Isolated finds around the world in regions where no sources are indicated have not been uncommon.

Natural deposits are worked by crushing, by gravity and flotation separations, and by removal of diamonds by their adherence to a layer of grease on a suitable table. The following products result: (1) diamond proper—distorted cubic crystalline gem-quality stones varying from colourless to red, pink, blue, green, or yellow; (2) bort—minute dark crystals of abrasive but not gem quality; (3) ballas—randomly oriented crystals of abrasive quality; (4) macles—triangular pillow-shaped crystals that are industrially useful; and (5) carbonado—mixed diamond–graphite crystallites containing other impurities.


Graphite occurs naturally in many areas, the deposits of major importance being in China, India, Brazil, Turkey, Mexico, Canada, Russia, and Madagascar. Both surface- and deep-mining techniques are used, followed by flotation, but the major portion of commercial graphite is produced by heating petroleum coke in an electric furnace. A better crystallized form, known as pyrolytic graphite, is obtained from the decomposition of low-molecular-weight hydrocarbons by heat. Graphite fibres of considerable tensile strength are obtained by carbonizing natural and synthetic organic fibres.


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