Properties of Giant Covalent StructuresOxford AQA IGCSE Chemistry: Revision notes
Section 1
What are giant covalent structures?
Atoms that share electrons through covalent bonding can form huge networks called giant covalent structures, also known as macromolecules. Every atom in the structure is linked to its neighbours by strong covalent bonds, and this pattern repeats throughout the whole substance.
Examples include diamond, graphite, and silicon dioxide.
Section 2
Why do giant covalent structures have very high melting points?
All the atoms in a giant covalent structure are linked by strong covalent bonds that extend throughout the whole structure, not just between small groups of atoms.
To melt the substance, a very large number of these strong covalent bonds must be broken, which requires a very large amount of energy — this is why giant covalent structures have such high melting points compared with simple molecular substances.
Always explain high melting points in terms of breaking many strong covalent bonds, not 'strong forces' in general — examiners want 'covalent bonds' named specifically.
Section 3
Comparing examples of giant covalent structures
| Structure | Bonds per atom | Key property |
|---|---|---|
| Diamond | 4 (carbon) | Extremely hard |
| Graphite | 3 (carbon), layered | Soft, conducts electricity |
| Silicon dioxide | Similar to diamond | Very hard, high melting point |
Despite differences in specific properties (e.g. hardness, conductivity), all giant covalent structures share the feature of a very high melting point because of their extensive covalent bonding.
Must Know
- Giant covalent structures (macromolecules) form when atoms share electrons across a huge, repeating network
- Examples: diamond, graphite, silicon dioxide
- All atoms are linked by strong covalent bonds throughout the structure
- This gives giant covalent structures very high melting points, because breaking the structure means breaking many strong covalent bonds
- Unlike simple molecules, there are no separate small units — the whole structure is one giant network
That's the notes covered.
Carry on to the next subtopic.