Carbon sheets, cages and tubes: how the arrangement of atoms controls the properties of graphene and fullerenes

1. Both graphene and fullerenes are structures made only from carbon atoms.
   1. In each one the atoms are held together by strong covalent bonds, but they are arranged into very different shapes.
2. Graphene is a single flat layer of carbon atoms.
3. Fullerenes are hollow molecules shaped as cages or tubes.
4. The way the carbon atoms are arranged and bonded controls each structure's properties and uses.

Graphene: strong bonds and mobile electrons make one thin sheet useful

1. Graphene is a single layer of graphite that is only one carbon atom thick.
2. Its carbon atoms are joined in a flat pattern of hexagonal rings.
3. Each carbon atom forms three strong covalent bonds to three neighbouring carbon atoms.
4. These covalent bonds run right through the whole sheet, forming one giant covalent structure.
   1. This gives graphene a very high tensile strength, so it resists being stretched or pulled apart.
5. Each carbon atom has four outer electrons but uses only three in bonding, leaving one delocalised electron.
   1. These delocalised electrons are free to move across the whole sheet and carry electrical charge.
6. Graphene is therefore a good conductor of electricity, even though it contains no metal.
7. Graphene is also very thin, flexible and almost transparent.
   1. These properties make it useful in electronic circuits, touchscreens and sensors.
8. Adding strong, low-mass graphene to another material can make a composite with improved strength.

Fullerenes: rings of carbon close up to form hollow molecules

1. Fullerenes are molecules made entirely of carbon atoms with hollow shapes.
2. Their structure is based on hexagonal rings of carbon atoms.
3. They may also contain rings of five or seven carbon atoms.
   1. These five- and seven-membered rings let the surface curve round and close into a cage or tube.
4. Buckminsterfullerene, formula $C_{60}$, was the first fullerene to be discovered.
5. It contains 60 carbon atoms arranged in a roughly spherical cage.
   1. Its mix of pentagons and hexagons gives it a shape like a football.

Carbon nanotubes: long, strong cylinders that reinforce materials and carry charge

1. Carbon nanotubes are cylindrical fullerenes whose carbon atoms are bonded into a hollow tube.
2. They have a very high length-to-diameter ratio, meaning they are extremely long compared with how wide they are.
3. Strong covalent bonds between the carbon atoms give nanotubes very high tensile strength.
4. This lets nanotubes reinforce composite materials without adding much mass.
   1. They are useful wherever a material must be both strong and light.
5. Delocalised electrons can move along a nanotube, so it conducts electricity.
6. Their tiny size and conductivity make nanotubes useful in electronics and nanotechnology.
7. Nanotubes also conduct thermal energy well, helping to move heat through a material.

Reading diagrams: telling a sheet, a cage and a tube apart

1. Recognise graphene as one flat sheet of joined hexagonal rings, one atom thick.
2. Recognise a fullerene as a separate hollow cage or tube of carbon rings.
3. Recognise Buckminsterfullerene as a roughly spherical cage of 60 carbon atoms.
4. Recognise a carbon nanotube as a long, narrow, hollow cylinder much longer than it is wide.
5. Hexagonal rings alone do not make a structure graphene, because a closed cage or cylinder is a fullerene.
   1. So use the overall shape as well as the ring pattern when you name a structure.