In graphite, each carbon makes three covalent bonds to other carbons. They form hexagonal rings in sheets. The sheets are stacked in layers. The fourth outer electron from each carbon is delocalised and can move through the structure.
Covalent bonds within each sheet are strong. The forces between the layers are weak. Layers can slide over each other, making graphite soft and slippery. This is useful in pencil leads and some lubricants.
Many strong covalent bonds must be broken to melt graphite, so it has a very high melting point. Graphite conducts electricity because its delocalised electrons move and carry charge. It is a non-metal that conducts.
Graphene is a single layer of graphite, one atom thick. Each carbon bonds to three others. Strong covalent bonds make the sheet strong, and delocalised electrons let it conduct. It is useful in electronics and in composite materials that combine useful properties.
| Diamond | Graphite | |
|---|---|---|
| Bonds per carbon | 4 | 3 |
| Arrangement | 3D network | Stacked sheets |
| Electrical conduction | No | Yes: delocalised electrons |
| Hardness | Very hard | Soft: layers slide |
Graphite: three bonds per carbon, weak forces between layers and mobile delocalised electrons. Graphene is one sheet.
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