Giant Covalent Structures — AQA GCSE Chemistry
Some covalent substances form huge networks of atoms joined by strong covalent bonds, giving them very high melting points.
What are giant covalent structures?
A giant covalent structure is a huge network of atoms all joined by strong covalent bonds. Because so many strong bonds must be broken, these substances have very high melting and boiling points.
Key examples
- Diamond — each carbon atom is bonded to four others in a rigid 3D lattice. It is very hard and has a very high melting point; it does not conduct electricity (no free electrons).
- Graphite — each carbon is bonded to three others, forming layers that can slide over each other. This makes graphite soft and slippery (a good lubricant). Each carbon has one delocalised electron, so graphite conducts electricity and heat.
- Graphene — a single layer of graphite, one atom thick; extremely strong, light and conductive.
- Silicon dioxide (silica/sand) — a giant covalent structure with a high melting point, similar to diamond.
Fullerenes (Separate)
Fullerenes are molecules of carbon shaped as hollow tubes or spheres (e.g. buckminsterfullerene C₆₀ and carbon nanotubes). They are used in drug delivery, catalysts and as strong, light materials.
Exam tips
- Giant covalent structures have very high melting points (many strong bonds).
- Diamond = 4 bonds, hard, non-conducting; graphite = 3 bonds, layers, conducts (delocalised electrons).
- Graphene is a single layer of graphite.
- Link each property back to the structure and bonding.