Recognise graphene and fullerenes from diagrams and descriptions of their…

The idea

Graphene is a giant covalent form of carbon, whereas fullerenes are simple molecular forms. In graphene, each carbon atom bonds covalently to three others, forming a single sheet one atom thick of interlocking hexagons; the fourth electron is delocalised, allowing electrical conductivity. Fullerenes are closed cage molecules of carbon atoms, typically with hexagonal and pentagonal rings. Buckminsterfullerene, C₆₀, is a hollow sphere of 60 carbon atoms. While each carbon atom in a fullerene also forms three covalent bonds, fullerenes are simple molecular because they form discrete, finite molecules rather than a continuous giant lattice. To recognise them, note the overall shape: a flat sheet indicates graphene, while a closed sphere or cylinder indicates a fullerene.

What earns the marks

• Graphene is a single layer of carbon atoms, one atom thick, arranged in a regular hexagonal lattice.
• Each carbon atom in graphene forms three covalent bonds to other carbon atoms, leaving one delocalised electron per atom, which allows graphene to conduct electricity.
• Fullerenes are molecules of carbon in closed cages or tubes, containing hexagonal rings and often pentagonal rings; buckminsterfullerene has the formula C₆₀ and a hollow spherical shape.
• Carbon nanotubes are cylindrical fullerenes formed from rolled sheets of hexagonal carbon rings.
• Fullerenes are simple molecular substances with weak intermolecular forces between discrete molecules, unlike the continuous giant covalent lattice of graphene.
• Recognition from a diagram requires identifying the overall shape: a flat sheet for graphene, or a closed sphere or cylinder for a fullerene.

Common mistakes and how to put them right

• Describing graphene as a three-dimensional giant lattice like diamond.

  Put it right by stating graphene is a single two-dimensional sheet one atom thick.

• Stating that each carbon atom in graphene or a fullerene forms four covalent bonds.

  Put it right by counting three bonds per carbon atom, with the remaining electron delocalised.

• Classifying fullerenes as giant covalent structures.

  Put it right by explaining that fullerenes are simple molecular substances made of discrete, finite cage or tube molecules.

Exam tips

• When a diagram is given, identify the overall shape—flat sheet, closed sphere, or cylinder—before deciding whether the structure is graphene or a fullerene.
• If asked to compare, state one similarity, such as carbon atoms joined by covalent bonds, and one difference, such as graphene being a giant covalent structure while fullerenes are simple molecular.