Carbon

Carbon is a chemical element with atomic number Z = 6, i.e., the carbon nucleus has charge 6e, where e is the elementary charge, and carbon takes the sixth position in the periodic table of elements. The chemical symbol of carbon is C.

The electron configuration is [He]2s²2p²

One twelfth of the mass (formerly called atomic weight) of the most abundant isotope ¹²C is by definition the unified atomic mass unit: A(¹²C) ≡ 1 u. The atomic mass averaged over the naturally occurring isotopes is 12.0107 u.

Carbon has a melting point of 3550 °C (diamond) and a boiling point of 3800 °C (sublimation)

One of the most widely distributed and abundant of all elements, carbon is a constituent of all organic matter. Diamond, graphite, and fullerenes are non-organic compounds consisting of carbon only; these are known as allotropes of carbon. Most organic carbon compounds contain hydrogen; those that contain oxygen as well include the extensive class of carbohydrates.

Carbon is abundant in the sun, stars, comets, and atmospheres of most planets. Carbon is also found in the form of microscopic diamonds in some meteorites.

Plastics, drugs, animal and plant tissue, foods, textile, wood, paper, and many other common substances contain carbon. Fossil fuels (coal, petroleum, natural gas, etc.) are compounds of carbon.

The greenhouse gas carbon dioxide CO₂ is an oxide of carbon, as is the poisonous gas carbon monoxide (CO).

Isotopes

There are seven isotopes of carbon.

¹²C was adopted as the basis of atomic weights by the International Union of Pure and Applied Chemistry in 1961. ¹²C Comprises about 98.89% of all carbon on Earth.

¹³C is another natural, stable isotope of carbon comprising about 1.1% of all natural carbon on Earth.

¹⁴C, an unstable isotope with a half-life of 5,715 years, is commonly used to date such materials as wood, archaeological specimens, etc.

Forms

Carbon occurs naturally in three allotropic forms: graphite, diamond, and fullerines. There is a fourth form, Ceraphite (also known as "white" carbon), which may also exist.

Graphite occurs in two forms: alpha and beta. They have identical physical properties and differ only in their crystalline structure. Naturally occurring graphites are reported to contain as much as 30% of the beta form, whereas synthetic materials contain only the alpha form. The alpha type can be converted to the beta by mechanical manipulation, and the beta form will revert to the alpha when it is heated above 1000 °C.

A new allotropic form of carbon was produced in 1969. Ceraphite, white carbon, was produced when pyrolytic graphite was sublimated at low pressures. Under free-vaporization conditions above approximately 2550 °K, "white" carbon will form as small transparent crystals. Little information is presently available about this allotrope.