Fullerenes

Fullerenes are molecules made entirely of carbon atoms joined together to form hollow shapes. The atoms form rings, mainly six-membered rings, although some fullerenes also contain five-membered or seven-membered rings. These rings join to form a hollow cage or a related hollow framework.

A fullerene is a discrete molecule: it is a separate structure with its own atoms and bonds. This differs from graphene, which consists of a continuous layer of carbon atoms rather than separate hollow molecules.

Recognising fullerene structures

In a structure diagram, look for carbon atoms joined into rings that make a hollow framework. The atoms may be shown at the corners of the rings, with lines representing the bonds between them. A fullerene may be described as a hollow cage even if the diagram shows only its outline rather than the empty space inside.

Buckminsterfullerene

Buckminsterfullerene, $$\ce{C60}$$, was the first fullerene discovered. Each molecule contains 60 carbon atoms joined in a roughly spherical cage. Its carbon atoms form five-membered and six-membered rings.

Carbon nanotubes

A carbon nanotube is a cylindrical fullerene: a hollow, tube-shaped structure made of joined carbon atoms. The tube is extremely narrow compared with its length, so it has a very high length-to-diameter ratio.

The carbon atoms are joined by strong bonds in a continuous network. This makes nanotubes very strong, and their long, narrow shape makes them useful for reinforcing materials. For example, adding nanotubes to an advanced material can increase its strength.

Carbon nanotubes also have useful electrical properties. Depending on their structure, they can conduct electricity or behave as semiconductors. This makes them useful in electronics, where their tiny dimensions allow them to be used in very small components.

Their strength, electrical behaviour and nanoscale size also make carbon nanotubes useful in nanotechnology, where materials and structures are designed on an extremely small scale. These uses show how the particular structure of a fullerene can give it useful properties.

Graphene

Graphene is a form of carbon consisting of a single layer of graphite, just one atom thick. Its carbon atoms form a flat lattice of hexagons. Each carbon atom is covalently bonded to three others, creating a giant covalent structure with strong bonds throughout the layer.

Each carbon atom uses three electrons to form these covalent bonds. Its remaining outer electron is delocalised: it is not fixed to one bond and can move through the layer. These moving electrons carry charge, so graphene conducts electricity.

Graphene’s thinness, strength and electrical conductivity make it useful in electronics. It can also be added to composite materials when a light but strong material is needed.