Giant Covalent Molecules

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A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Giant Covalent Molecules: Diamond and silicon dioxide

  • Small covalent molecules have low melting and boiling points. This is because they have very weak intermolecular forces.
  • Giant covalent molecules have millions of strong covalent bonds.
  • Giant covalent molecules are always solids at room temperature. They always have high melting and boiling points.
  • Diamond is formed from the element carbon. Each carbon atom forms four strong covalent bonds. They cannot conduct electricity because there are no free electrons to carry electrical charge.
  • Silicon dioxide is another example of a giant covalent molecules. It consists of silicon and oxygen atoms.


  • Graphite has a high melting and boiling point.
  • Graphite is soft and slippery.
  • Graphite is an excellent conductor of both electricity and of heat.
  • Graphite is formed from the element carbon. Each carbon atom forms three covalent bonds.
  • The carbon atoms form hexagonal rings. The hexagonal rings are in layers. There are no covalent bonds between the layers so they can slide.
  • Delocalised electrons can move. This means they can conduct thermal energy (heat) and electricity.

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