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AQA GCSE Chemistry · 8462
AQA 8462 · 4.2.3.3 Check the specification (PDF) (opens in a new tab)
Carbon atoms can join in different arrangements, producing allotropes with different properties. Graphite is built from layers of carbon atoms arranged in hexagonal rings. Graphene is just one of those layers, separated from the others: a sheet only one atom thick. Within the sheet, each carbon atom forms strong covalent bonds with three neighbours.
Those bonds make graphene very strong, despite its tiny thickness. Each carbon atom also contributes an electron that is delocalised rather than fixed in a particular bond. These electrons can move across the sheet and carry electrical charge, so graphene conducts electricity. Its strength makes it useful in composite materials, where it can help reinforce another material; its conductivity makes it useful in electronics. Being only one atom thick also makes it very light and nearly transparent.
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.
Buckminsterfullerene, the first fullerene discovered, has the formula . Its 60 carbon atoms form a hollow sphere resembling a football, with hexagonal and pentagonal rings. The hollow shape can hold other molecules, which is why fullerenes are investigated for uses such as carrying medicines.
Recognise graphene by its flat sheet, buckminsterfullerene by its hollow spherical cage, and a carbon nanotube by its long hollow cylinder.
A carbon nanotube is a cylindrical fullerene. Picture a sheet of hexagonally arranged carbon atoms curved into a hollow tube. It has a very high length-to-diameter ratio: it is long compared with how wide it is. Strong covalent bonds make nanotubes strong while their small diameter keeps them light. They can also conduct electricity because they have delocalised electrons.
These properties make nanotubes useful in nanotechnology, electronics and specialised materials. For example, they can reinforce a composite used in sports equipment without adding much weight. When reading a diagram, look for the shape as well as the bonds: a flat hexagonal sheet is graphene, a rounded hollow cage is a fullerene such as C₆₀, and a long hollow cylinder is a carbon nanotube.
Graphene's strong covalent bonds give strength for composites; delocalised electrons give conductivity for electronics. Nanotubes are strong and light, so can reinforce materials, and their conductivity is useful in electronics. Hollow fullerene cages can carry other molecules.
In a structure diagram, distinguish a flat, one-atom-thick graphene sheet from a hollow spherical fullerene or a long, hollow nanotube.
Link each property to structure: strong covalent bonds explain strength; delocalised electrons explain electrical conductivity.
Do not describe buckminsterfullerene as a giant covalent structure. Each C₆₀ sphere is a separate molecule.
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Allotrope
One of the different structural forms of an element, produced when its atoms are bonded or arranged differently.
Graphene
A single, one-atom-thick layer of graphite in which carbon atoms form a sheet of hexagonal rings.
Fullerene
A molecule made only of carbon atoms joined into a hollow shape, usually based on hexagonal rings.
Buckminsterfullerene
A spherical fullerene molecule containing 60 carbon atoms, with the formula C₆₀.
Carbon nanotube
A long, hollow, cylindrical fullerene made of bonded carbon atoms.
Delocalised electron
An electron that is not confined to one bond and can move through part of a structure.
Put your knowledge into practice — try past paper questions for Chemistry
Allotrope
One of the different structural forms of an element, produced when its atoms are bonded or arranged differently.
Graphene
A single, one-atom-thick layer of graphite in which carbon atoms form a sheet of hexagonal rings.
Fullerene
A molecule made only of carbon atoms joined into a hollow shape, usually based on hexagonal rings.
Buckminsterfullerene
A spherical fullerene molecule containing 60 carbon atoms, with the formula C₆₀.
Carbon nanotube
A long, hollow, cylindrical fullerene made of bonded carbon atoms.
Delocalised electron
An electron that is not confined to one bond and can move through part of a structure.