Polymorphs of carbon. The element carbon can occur in more than one form – the different forms are known as polymorphs. Diamond. In diamond the carbon atoms are arranged in a giant covalent network. Each carbon atom is bonded to 4 other carbon atoms arranged tetrahedrally round each other. The strong covalent bonds gives diamond a very high melting point and makes diamonds very strong. As all four electrons in the outer electron energy level are shared with other carbon atoms there are no electrons to carry an electric current. Diamonds are non- conductors of electricity.

Graphite. In graphite the carbon atoms are arranged in layers. Within the layer the carbon atoms are covalently bonded to three other carbon atoms. Between the layers there are weak van der Waals forces. The weak van der Waals forces between the layers makes graphite quite soft. With only three of the four electrons in the outer energy level shared with other carbon atoms there are ‘delocalised’ electrons in the structure. This makes graphite a conductor of electricity.

Fullerine. In the most common form of fullerine there are 60 carbon atoms in a large covalent molecule. Inside the C 60 molecule the carbon atoms are bonded by strong covalent bonds. Between the C 60 molecules there are weak van der Waals forces.