Some covalent substances form giant (network) covalent structures – continuous 3D lattices of covalently bonded atoms with no discrete molecules. They share many physical properties with ionic compounds (very high melting points) but for different reasons.
| Structure | Bonding | Hybridisation | Key Properties |
|---|---|---|---|
| Diamond | Each C bonded to 4 others (tetrahedral) | sp³ | Hardest natural substance, insulator, very high mp, transparent |
| Graphite | Each C bonded to 3 others (planar layers) | sp² | Soft/slippery (layers slide), conducts electricity (delocalised e⁻), high mp |
| Graphene | Single layer of graphite | sp² | Strongest known material, excellent conductor, transparent, flexible |
| C₆₀ Fullerene | 60 carbons in truncated icosahedron | sp² | Molecular (soluble in non-polar solvents), semiconductor |
| SiO₂ | Each Si bonded to 4 O atoms (3D network) | sp³ | Very high mp, hard, insulator (no delocalised electrons) |
🔑 Why Graphite Conducts
Each carbon is sp² hybridised with 3 bonding pairs in a trigonal planar arrangement. The 4th electron occupies an unhybridised p-orbital perpendicular to the plane. These p-orbitals overlap laterally across the entire layer, creating a sea of delocalised π electrons that can carry a current.
⚠️ Examiner Trap – Fullerene is NOT Giant
C₆₀ fullerene is a simple molecular substance – it forms discrete molecules. It is soluble in non-polar solvents and has a comparatively low melting point. Do not confuse it with the giant covalent allotropes.
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