Fullerene

A fullerene is a molecule of carbon atoms joined into a hollow shape. Its structure is based on hexagonal rings, but it may also include rings of five or seven carbon atoms. Unlike graphene's extended sheet, a fullerene such as buckminsterfullerene is an individual molecule.

In fullerenes, the atoms form separate hollow molecules. In graphene, they form a continuous sheet. The carbon–carbon covalent bonds are strong in both, but the overall shape and the way electrons can move explain why the materials behave differently.

Diamond, graphite, graphene and fullerenes are all made only of carbon. They are allotropes: forms of the same element whose atoms are arranged differently. A carbon atom can form four covalent bonds, but its bonds need not produce the same structure every time.

Some carbon nanoparticles are fullerenes, in which carbon atoms are joined in rings to make hollow structures. The rings may be arranged into a roughly ball-shaped molecule or into a long tube. These shapes supply properties that cannot be explained by small size or surface area alone.