Allotropy is the property of some chemical elements to exist in two or more different forms, or allotropes, when found in nature. There are several allotropes of carbon.

Carbon has electronic configuration [He]2s²2p², and main formal oxidation state +4 (there are other oxidation states, but all use all of carbons valence electrons in bonding). Alongside the central role of Carbon in Organic Chemistry, it forms numerous compounds, both inorganic and organometallic.

There are two main isotopes, with relative abundances: ¹²C (98.9%, I=0), and ¹³C (1.1%, I=0.5). It is the nuclear spin, and the half-integer value of the nuclear spin for ¹³C gives it its usefulness in structure determination by NMR.

Elemental carbon occurs in several different forms, ie. it displays a complex allotropy. The main forms are diamond and graphite, and they exhibit markedly different properties due to the very different structures they adopt.

Allotropes of carbon: a) Diamond, b) Graphite, c) Lonsdaleite, d) C60 (Buckminsterfullerene or buckyball), e) C540, f) C70, g) Amorphous carbon, and h) single-walled carbon nanotube, or buckytube.