Diamond and graphite

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

Diamond

Structure and bonding

Diamond is a giant covalent structure in which:

  • each carbon atom is joined to four other carbon atoms by strong covalent bonds
  • the carbon atoms form a regular tetrahedral network structure
  • there are no free electrons
Covalent structure of diamondCarbon 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.

Diamond has a very high melting point because a lot of energy is required to break the strong covalent bonds between the atoms. It does not conduct electricity because it has no free electrons.

Graphite

Structure and bonding

Graphite has a giant covalent structure in which:

  • each carbon atom forms three covalent bonds with other carbon atoms
  • the carbon atoms form layers of hexagonal rings
  • there are no covalent bonds between the layers
  • there is one non-bonded - or delocalised - electron from each atom
Covalent structure of graphiteDotted lines represent the weak forces between the layers in graphite

Properties and uses

Graphite has delocalised electrons, just like metals. These electrons are free to move between the layers in graphite, so graphite can conduct electricity. This makes graphite useful for electrodes in batteries and for electrolysis.

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

Question

Explain why diamond does not conduct electricity and why graphite does conduct electricity.

Diamond does not conduct electricity because it has no charged particles that are free to move. Graphite does conduct electricity because it has delocalised electrons which move between the layers.