Graphene and fullerenes — AQA GCSE Chemistry

Graphene is one layer of graphite, just one atom thick, in which carbon atoms are arranged in a hexagonal lattice. Each carbon atom bonds covalently to three others, leaving one delocalised electron per atom. Because the layer is only one atom thick, graphene is extremely thin, has a very large surface area for its mass, and is strong yet flexible. The delocalised electrons make it an excellent electrical conductor, which is why it is used in electronics, for example in fast transistors, touchscreens and conductive inks. Its strength, low mass and large surface area make it useful in composites, where it is added to materials such as plastics to reinforce them or to add conductivity. Graphene is not a molecule with a fixed small number of atoms; it is a single extended layer, so its properties come from its giant covalent sheet structure.

To explain graphene's properties, start from its structure: it is a single layer of graphite, one atom thick, with carbon atoms covalently bonded to three neighbours in a hexagonal lattice. Each carbon atom contributes one delocalised electron, so the layer contains mobile charge carriers and conducts electricity. The strong covalent bonds throughout the layer make graphene very strong, while the single-layer sheet is flexible because it is so thin. Being one atom thick gives a very large surface area per gram, which is useful in sensors and composites. The extended covalent network also gives a very high melting point, because melting would require breaking many strong covalent bonds. A good explanation always names the structural feature, then the property, then the use or consequence, for example delocalised electrons lead to conductivity, which suits electronic circuits.

Fullerenes are molecular forms of carbon in which the atoms join to make closed, hollow cages or tubes. The most familiar is buckminsterfullerene, C₆₀, which has 60 carbon atoms arranged in pentagons and hexagons like a football. Other fullerenes form tubes, called carbon nanotubes. Each carbon atom bonds to three others, so the shape closes into a hollow structure. Spherical fullerenes like C₆₀ are simple molecules with fixed formulae and relatively low melting points, as only weak intermolecular forces need to be overcome. In contrast, carbon nanotubes are extended cylindrical structures with variable lengths and high melting points. Their hollow cages can enclose other atoms or molecules, which is useful in drug delivery, and nanotubes are strong and can conduct electricity, making them useful in electronics and materials.

Fullerenes are molecular forms of carbon in which every carbon atom bonds to three others, producing curved cage-like or tubular molecules. The framework is built mainly from hexagonal rings of carbon atoms, exactly like the six-membered rings in graphite, but curvature is introduced by rings containing five or seven carbon atoms. A five-membered ring pulls the sheet into a dome, while a seven-membered ring opens it out; combining these with hexagons closes the structure into shapes such as the spherical buckminsterfullerene, C₆₀. Although each carbon uses three covalent bonds within the cage, leaving one delocalised electron per atom, spherical fullerenes like C₆₀ do not conduct electricity as bulk solids because electrons cannot easily jump between discrete molecules. Recognising the ring sizes in a diagram is the key skill.

A carbon nanotube is a fullerene in which the carbon cage is rolled into a long, hollow cylinder instead of a closed ball. The cylinder wall is a curved sheet of hexagonal carbon rings, with each carbon bonded to three others, and the ends may be capped by curved rings containing five-membered rings. Nanotubes are typically nanometres in diameter but can be micrometres or millimetres long, so the length to diameter ratio is extremely large, often thousands to one. This high aspect ratio, together with strong covalent bonding along the tube and delocalised electrons, gives nanotubes exceptional tensile strength, stiffness and electrical conductivity. They are therefore used in composite materials, nanoscale electronics and as molecular wires.

The distinctive structures of fullerenes, including carbon nanotubes, give them properties that are exploited in three broad areas. In nanotechnology, the nanometre-scale dimensions of spherical fullerenes allow them to be used as delivery vessels for drugs, as catalysts and as lubricants. In electronics, carbon nanotubes are excellent conductors of electricity because of their delocalised electrons and extended structure, allowing them to act as tiny wires or components in circuits. In materials, the great tensile strength and low mass of carbon nanotubes make them valuable in lightweight composites for sports equipment, vehicles and construction. The key exam skill is to link a named property, such as high tensile strength or electrical conductivity, to a specific use rather than listing uses without justification.

This practical skill statement combines identification with application. Recognising graphene and fullerenes means interpreting a diagram or written description and using structural clues: graphene is a single flat layer of hexagonal carbon rings one atom thick, with each carbon bonded to three others; spherical fullerenes are closed cages of hexagons and five-membered rings; nanotubes are hollow cylinders with a very high length to diameter ratio. Once identified, students should be able to give uses of fullerenes, including carbon nanotubes, and justify them by linking to properties such as electrical conductivity, high tensile strength or nanoscale size. Answers should name the structure, state the evidence from the diagram or description, and then connect the structure to a use.