Diamond and graphite — two faces of carbon
Same element, different arrangements, wildly different properties.
Diamond and graphite are both made of pure carbon — but their atoms are arranged completely differently, giving radically different properties. They are allotropes of carbon.
Diamond. Every carbon atom forms FOUR strong covalent bonds to its neighbours, in a 3D tetrahedral lattice. Result:
- Extremely hard — strong bonds throughout the structure. Used in drill bits, cutting tools.
- Very high MP (~3 700 °C) — millions of covalent bonds to break.
- Doesn't conduct electricity — all four outer electrons are used in bonding (no free electrons).
Graphite. Each carbon forms THREE bonds, in flat hexagonal LAYERS. The fourth outer electron is delocalised within the layer. Result:
- Soft and slippery — layers slide easily over each other. Used in pencils and as a dry lubricant.
- Very high MP — covalent bonds INSIDE layers are very strong.
- CONDUCTS electricity in the plane of the layers — delocalised electrons can move. Used as electrodes.
- Diamond: 4 bonds per C, 3D lattice, very hard, doesn't conduct.
- Graphite: 3 bonds per C, flat layers, soft and slippery, conducts.
- Both very high MP — covalent bonds are strong.