Diamond and graphite

Diamond and graphite are different forms of the element carbon. They both consist of giant covalent network structures of carbon atoms, joined together by covalent bonds. However the shape of their structures and their properties are different.

Diamond

Structure and bonding

Diamond is a giant covalent substance in which:

  • each carbon atom is joined to four other carbon atoms by covalent bonds
  • the carbon atoms form a regular tetrahedral network structure
  • there are no free electrons
The structure of diamond.Carbon atoms in diamond form a 'tetrahedral' arrangement

Properties and uses

The rigid network of carbon atoms, held together by strong covalent bonds, makes diamond very hard. This makes it useful for cutting tools, such as diamond-tipped glass cutters and oil rig drills.

Graphite

Structure and bonding

Graphite is a giant covalent substance in which:

  • each carbon atom is joined to three other carbon atoms by covalent bonds
  • the carbon atoms form a hexagonal layered network structure
  • the layers have weak forces between them and can slide over each other
  • each carbon atom has one un-bonded outer electron
  • these un-bonded electrons are delocalised, and are free to move
The structure of graphite ball and stick diagram.Dotted lines model the weak forces between the layers in graphite

Properties and uses

Delocalised electrons are free to move through the structure of graphite, so graphite can conduct electricity. This makes it useful for electrodes in batteries and for electrolysis.

The layers in graphite can slide over each other because the forces between them are weak. This makes graphite slippery, so it is useful as a lubricant.