Very large molecules

Graphene

Graphene is another form of carbon. Its structure resembles a single layer of graphite. Graphene has a very high melting point and is very strong because of its large regular arrangement of carbon atoms joined by covalent bonds. Like graphite it conducts electricity well because it has delocalised electrons that are free to move across its surface.

Fullerenes

A fullerene is a molecular form of the element carbon. Two examples of fullerenes are nanotubes and buckyballs.

Nanotubes

A nanotube resembles a layer of graphene, rolled into a tube shape. Nanotubes have high tensile strength, so they are strong in tension and resist being stretched. Like graphene, nanotubes are strong and conduct electricity because they have delocalised electrons.

Covalent structure of a nanotubeNanotubes can be several millimetres long but only a few nanometres wide

Buckyballs

Buckyballs are spheres or squashed spheres of carbon atoms. They are made up of large molecules so are not classed as giant covalent networks. Weak intermolecular forces exist between buckyballs. These need little energy to overcome, so substances consisting of buckyballs are slippery and have lower melting points than graphite or diamond.

Covalent structure of buckminsterfullereneBuckminsterfullerene has sixty carbon atoms joined by covalent bonds

Polymers

Simple polymers consist of large molecules that contain chains of carbon atoms of no set size.

A model of a short section of a poly(ethene) molecule, a simple polymer. Polythene molecules will contain thousands of carbon atoms joined together in a chainA model of a short section of a poly(ethene) molecule, a simple polymer. Polythene molecules will contain thousands of carbon atoms joined together in a chain.
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