Carbon

Carbon, ₆C
	Graphite (left) and diamond (right), two allotropes of carbon
General properties
Allotropes	graphite, diamond
Appearance	graphite: black; diamond: clear
Standard atomic weight (Ar, standard)	[12.0096, 12.0116]
Carbon in the periodic table
	boron ← carbon → nitrogen
Atomic number (Z)	6
Group	group 14 (carbon group)
Period	period 2
Block	p-block
Element category	reactive nonmetal, sometimes considered a metalloid
Electron configuration	[He] 2s2 2p2
Electrons per shell	2, 4
Physical properties
Phase at STP	C: Solid
Sublimation point	3915 K (3642 °C, 6588 °F)
Density (near r.t.)	amorphous: 1.8–2.1 g/cm3 ; graphite: 2.267 g/cm3 ; diamond: 3.515 g/cm3
Triple point	4600 K, 10,800 kPa
Heat of fusion	graphite: 117 kJ/mol
Molar heat capacity	graphite: 8.517 J/(mol·K) ; diamond: 6.155 J/(mol·K)
Atomic properties
Oxidation states	−4, −3, −2, −1, 0, +1, +2, +3, +4 (a mildly acidic oxide)
Electronegativity	Pauling scale: 2.55
Ionization energies	1st: 1086.5 kJ/mol ; 2nd: 2352.6 kJ/mol ; 3rd: 4620.5 kJ/mol ; (more) ;
Covalent radius	sp3: 77 pm; sp2: 73 pm; sp: 69 pm
Van der Waals radius	170 pm
	Spectral lines of carbon
Other properties
Natural occurrence	C: Primordial
Crystal structure	graphite: simple hexagonal ; (black)
Crystal structure	diamond: face-centered diamond-cubic ; (clear)
Speed of sound thin rod	diamond: 18,350 m/s (at 20 °C)
Thermal expansion	diamond: 0.8 µm/(m·K) (at 25 °C)
Thermal conductivity	graphite: 119–165 W/(m·K) ; diamond: 900–2300 W/(m·K)
Electrical resistivity	graphite: 7.837 µΩ·m
Magnetic ordering	diamagnetic
Magnetic susceptibility	−5.9·10−6 (graph.) cm3/mol
Young's modulus	diamond: 1050 GPa
Shear modulus	diamond: 478 GPa
Bulk modulus	diamond: 442 GPa
Poisson ratio	diamond: 0.1
Mohs hardness	graphite: 1–2 ; diamond: 10
CAS Number	7440-44-0
History
Discovery	Egyptians and Sumerians (3750 BCE)
Recognized as an element by	Antoine Lavoisier (1789)
Main isotopes of carbon
	view; talk; edit; \| references

Carbon is a very important chemical element, with a chemical symbol of C. All known life on Earth needs it to survive. Carbon has atomic mass 12 and atomic number 6. It is a nonmetal, meaning that it is not a metal.

When iron is alloyed with carbon, hard steel is formed. Carbon in the form of coal is an important fuel.

Chemistry of carbon

A whole type of chemistry, called organic chemistry, is about carbon and its compounds. Carbon makes many types of compounds. Hydrocarbons are molecules with carbon and hydrogen. Methane, Propane, and many other fuels are hydrocarbons. Many of the substances that people use daily are organic compounds.

Carbon, hydrogen, nitrogen, oxygen, and some other elements like sulfur and phosphorus together form most life on earth (see List of biologically important elements). Carbon forms a very large number of organic compounds because it can form strong bonds with itself and with other elements. Because of the amounts of carbon living things have, all organic things are considered "carbon-based".

Each carbon atom usually forms four chemical bonds, which are strong connections to other atoms to form molecules. The kind of bond that carbon makes is called a covalent bond. These bonds allow carbon to form many kinds of small and large molecules. A molecule of methane is the smallest; it has four hydrogen atoms bonded to carbon. The bonds can be double bonds, meaning that two bonds form between carbon and another atom to make a stronger connection. For example, carbon dioxide has two oxygen atoms, and each one is double bonded to carbon. Carbon can even form three bonds with another atom, called a triple bond. For example, in the gas acetylene carbon forms a triple bond with another carbon atom.

By bonding to other carbon atoms, carbon can form long chain-shaped molecules, called polymers, such as plastics and proteins. Atoms of other elements can be part of the long polymer chains, often nitrogen or oxygen.

Pure carbon forms diamond by bonding to four other carbon atoms in a three dimensional crystal. It forms graphite by bonding to three other carbon atoms to form thin flat layers.

Etymology

The name of carbon comes from Latin carbo, meaning charcoal. In many foreign languages the words for carbon, coal and charcoal are synonyms.

Types of carbon

Main page: Allotropes of carbon

Carbon in nature is found in three forms called allotropes: diamond, graphite, and fullerenes. Graphite, with clay, is in pencils. It is very soft. The carbon atoms in it make rings, which are on top of each other and slide very easily. Diamonds are the hardest natural mineral. Fullerenes are a "soccer ball" shape of carbon. They are mostly of interest to science. A special, man-made, tube-shaped allotrope of carbon is the carbon nanotube. Carbon nanotubes are very hard, so they might be used in armor. Nanotubes might be useful in nanotechnology.

There are 10 million known carbon compounds.

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

Radiocarbon dating

Main page: Radiocarbon dating

A radioactive isotope of carbon, carbon-14, can be used to figure out how old some objects are or when something died. As long as something is on the surface of the earth and taking in carbon, the amount of carbon-14 stays the same. When an object stops taking in carbon, the carbon-14 amount goes down. Because the half-life (how long it takes for half of a radioactive isotope to go away) of carbon-14 is 5730 years,^[17] scientists can see how old the object is by how much carbon-14 is left.

Where carbon is

Carbon is in many places in the universe. It was first made in old stars. Carbon is the fourth most common element in the sun.^[17] The atmospheres of Venus and Mars are mostly carbon dioxide.^[18]

Carbon is important to the human body and other living things, and it is the second most common element in the human body, at 23% of all body weight.^[17] It is also a key part of many biological molecules (molecules used in life).

Most of the carbon on Earth is coal. Graphite is in many (typically desert) areas, including Sri Lanka, Madagascar, and Russia. Diamonds are rare and are found largely in Africa. Carbon is also in some meteorites.

Carbon Media

Theoretically predicted phase diagram of carbon, from 1989. Newer work indicates that the melting point of diamond (top-right curve) does not go above about 9000 K.
A large sample of glassy carbon
Some allotropes of carbon: a) diamond; b) graphite; c) lonsdaleite; d–f) fullerenes (C₆₀, C₅₄₀, C₇₀); g) amorphous carbon; h) carbon nanotube
Comet C/2014 Q2 (Lovejoy) surrounded by glowing carbon vapor
Graphite ore, shown with a penny for scale
Nearly octahedral diamond crystal in matrix.
"Present day" (1990s) sea surface dissolved inorganic carbon concentration (from the GLODAP climatology)
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 c. 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.
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.