4.2.3.1Diamond
In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity.
You should be able to explain the properties of diamond in terms of its structure and bonding — which means giving the reason, not repeating the property.
- Diamond
- a giant covalent structure in which each carbon atom forms four covalent bonds with other carbon atoms, making it very hard with a very high melting point and unable to conduct electricity
4.2.3.2Graphite
In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers.
In graphite, one electron from each carbon atom is delocalised.
The whole of graphite's behaviour follows from those two sentences. Three bonds instead of four leaves one outer electron spare — and that spare electron is what makes graphite conduct.
You should be able to explain the properties of graphite in terms of its structure and bonding, and you should know that graphite is similar to metals in that it has delocalised electrons. That comparison is worth holding on to: graphite is a non-metal that conducts, and it conducts for exactly the reason a metal does.
Common mistake
Graphite is soft because the layers slide, not because the bonds inside the layers are weak. Those bonds are strong covalent bonds — which is why the melting point is very high even though the substance is soft enough to write with.
- Graphite
- a form of carbon in which each atom forms three covalent bonds, making layers of hexagonal rings with no covalent bonds between the layers, and one delocalised electron per atom
- Delocalised electron
- an electron that is not bound to one atom and is free to move, which is what allows graphite and metals to conduct electricity
4.2.3.3Graphene and fullerenes
Graphene is a single layer of graphite and has properties that make it useful in electronics and composites.
You should be able to explain the properties of graphene in terms of its structure and bonding. Because it is one layer of graphite, the same explanations apply: each carbon atom is covalently bonded to three others, which makes the sheet very strong for its mass, and one electron per atom is delocalised, which makes it an excellent conductor. Being one atom thick, it is also almost transparent — which is what makes it useful in electronics, and why adding it to another material gives a composite that is stronger without being much heavier.
Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms, but they may also contain rings with five or seven carbon atoms. The first fullerene to be discovered was Buckminsterfullerene (C60), which has a spherical shape.
Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials.
You should be able to recognise graphene and fullerenes from diagrams and descriptions of their bonding and structure, and give examples of the uses of fullerenes, including carbon nanotubes.
Uses worth naming: fullerene cages can carry a drug molecule inside them for delivery in medicine; fullerenes have a very large surface area, which makes them useful as catalysts or catalyst supports; and carbon nanotubes are used to reinforce materials such as tennis racquets and aircraft parts, and in electronics, because they are strong along their length and conduct.
Common mistake
A fullerene is a molecule, not a giant structure. That is why fullerenes can dissolve and be handled as a substance made of separate particles, while diamond and graphite cannot.
- Graphene
- a single layer of graphite, one atom thick, which is very strong for its mass, an excellent conductor and almost transparent
Before you practise
- Diamond: four covalent bonds per carbon in a giant covalent structure — very hard, very high melting point, no delocalised electrons so no conduction.
- Graphite: three covalent bonds per carbon, layers of hexagonal rings with no covalent bonds between layers — soft and slippery, high melting point.
- In graphite one electron from each carbon atom is delocalised, so it conducts — like a metal.
- Graphene is a single layer of graphite, useful in electronics and composites.
- Fullerenes are hollow molecules of carbon based on hexagonal rings, which may also contain five- or seven-membered rings; the first was Buckminsterfullerene, C60.
- Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios, useful for nanotechnology, electronics and materials.
- Always answer these questions as structure → property, never property alone.