Diamond & Graphite (CIE IGCSE Chemistry)

What is the structure of graphite?

• Each carbon atom in graphite is bonded to three others forming layers of hexagons, leaving one free electron per carbon atom which becomes delocalised
• The covalent bonds within the layers are very strong, but the layers are attracted to each other by weak intermolecular forces

Diagram to show the bonding and structure in graphite

The structure and bonding in graphite

• Diamond and graphite are allotropes of carbon which have giant covalent structures
• Both substances contain only carbon atoms but due to the differences in bonding arrangements they are physically completely different
• Giant covalent structures contain billions of non-metal atoms, each joined to adjacent atoms by covalent bonds forming a giant lattice structure

What is the structure of diamond?

• In diamond, each carbon atom bonds with four other carbons, forming a tetrahedron
• All the covalent bonds are identical, very strong and there are no intermolecular forces

Diagram to show the formation of a covalent bond

Diagram showing the structure and bonding arrangement in diamond

What are the properties and uses of graphite?

• Graphite conducts electricity 
  • Each carbon atom is bonded to three others leaving one free electron per carbon atom 
  • These free (delocalised) electrons exist in between the layers
  • They are free to move through the structure and carry charge
• Graphite has a high melting point
  • Graphite has a giant covalent structure
  • There are strong covalent bonds between the carbon atoms
  • These need lots of energy to break 
• Graphite is slippery 
  • Graphite is arranged in layers
  • Although the atoms within the layers are joined by strong covalent bonds, the layers have only weak intermolecular forces between them
  • As a result the layers can slide over each other
  • This property allows graphite to be used in pencils and as an industrial lubricant

What are the properties and uses of diamond?

• Diamond does not conduct electricity
  • All the outer shell electrons in carbon are held in the four covalent bonds around each carbon atom
  • As a result, there are no freely moving particles to carry a charge

• Diamond has a very high melting point
  • Diamond has a giant covalent structure
  • There are strong covalent bonds between the carbon atoms
  • These need lots of energy to break 
• It is extremely hard and dense
  • It has strong covalent bonds and each carbon atom is bonded to four other carbon atoms 
  • Diamond's hardness makes it very useful in cutting tools like drills 

• Diamond has the following physical properties:
  • It does not conduct electricity
  • It has a very high melting point
  • It is extremely hard and dense