Giant Covalent Structures

Specification Point 1.35:
  • Recall that graphite and diamond are different forms of carbon and that they are examples of giant covalent substances.
  • Diamond and graphite are allotropes of carbon which have giant covalent structures.
  • Allotropes are elements which exist in two or more different forms but in the same physical state. 
  • They generally differ in physical properties and may also differ in their chemical properties.

Diamond & Graphite, Edexcel GCSE Chemistry

Diamond and graphite are allotropes and are also giant covalent structures

Structure of Diamond & Graphite

Specification Point 1.36:
  • Describe the structures of graphite and diamond

Diamond

  • Each carbon atom bonds with four other carbon atoms, forming a tetrahedron.
  • All the covalent bonds are identical and strong with no weak intermolecular forces.
  • Diamond thus:
    • Does not conduct electricity.
    • Has a very high melting point.
    • Is extremely hard and dense (3.51 g/cm3).

Bonding in Diamond, Edexcel GCSE Chemistry

Diagram showing the bonding arrangement of the carbon atoms in diamond

Graphite

  • Each carbon atom is bonded to three others forming layers of hexagonal shapes, leaving one free electron per carbon atom.
  • These free electrons exist in between the layers and are free to move and carry charge, hence graphite can conduct electricity.
  • The covalent bonds within the layers are very strong but the layers are connected to each other by weak intermolecular forces only, hence the layers can slide over each other making graphite slippery and smooth.
  • Graphite thus:
    • Conducts electricity.
    • Has a very high melting point.
    • Is soft and slippery, less dense than diamond (2.25 g/cm3).

Bonding in Graphite, Edexcel GCSE Chemistry

Diagram showing the bonding arrangement of the carbon atoms in graphite

Uses of Diamond & Graphite

Specification Point 1.37:
  • Explain, in terms of structure and bonding, why graphite is used to make electrodes and as a lubricant, whereas diamond is used in cutting tools.

Diamond

  • Diamond’s hardness makes it very useful for purposes where extremely tough material is required.
  • It is used extensively in jewellery and in cutting tools
  • The cutting edges of discs used to cut bricks and concrete are tipped with diamonds. 
  • Heavy-duty drill bits and tooling equipment are also diamond tipped.

Graphite

  • Graphite’s weak intermolecular forces make it a useful material.
  • It is used in pencils (mixed with clay)  and as an industrial lubricant, in engines and in locks.
  • It is also used to make non-reactive electrodes for electrolysis since it can conduct electricity without participating chemically in the process.

Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.