Structure and Bonding of Carbon (C2.3)
Allotropes of carbon
Carbon forms several allotropes — different structural forms of the same element.
Diamond
- Each carbon atom forms 4 covalent bonds in a tetrahedral arrangement.
- Giant covalent structure extending in all directions.
- Properties: extremely hard (hardest natural material), high melting point, does not conduct electricity, transparent.
- Uses: cutting tools (drill bits, saw blades), jewellery, abrasives.
Graphite
- Each carbon atom forms 3 covalent bonds → hexagonal layers.
- One delocalised electron per carbon atom (free to move between layers).
- Layers held together by weak intermolecular forces.
- Properties: soft/slippery (layers slide), high melting point (within layers), conducts electricity (delocalised electrons), grey/black and opaque.
- Uses: pencil "lead" (layers slide onto paper), lubricant, electrodes in electrolysis and batteries.
Graphene
- A single layer of graphite — one atom thick hexagonal lattice.
- Properties: incredibly strong (stronger than steel), very light, conducts electricity and heat exceptionally well, flexible.
- Uses: next-generation electronics, composite materials (stronger, lighter), biomedical sensors.
Fullerenes
- Carbon atoms arranged in hollow structures: spheres, tubes, or other shapes.
- Buckminsterfullerene (C₆₀, "Buckyballs"): 60 carbon atoms in a sphere (resembles a football — hexagons and pentagons).
- Carbon nanotubes: cylindrical fullerenes; exceptional strength and conductivity.
Properties of fullerenes:
- Small molecules → relatively low melting points for carbon allotropes
- Can conduct electricity (delocalised electrons within structure)
- Very small size → can enter cells (medical drug delivery)
Uses:
- Drug delivery (C₆₀ can carry drug molecules to specific sites)
- Industrial lubricants (ball-bearing effect)
- Nanotubes in composite materials, electronics, nanotechnology
Comparison table
| Allotrope | Bonding | Conductivity | Hardness | Notable use |
|---|---|---|---|---|
| Diamond | 4 covalent bonds per C | None | Hardest | Cutting tools |
| Graphite | 3 covalent + delocalised | Yes | Soft | Electrodes, pencils |
| Graphene | 3 covalent + delocalised | Excellent | Very strong | Electronics |
| C₆₀ | Mixed (5- and 6-membered rings) | Some | — | Drug delivery |
| Nanotubes | Cylindrical hexagonal | Excellent | Very high | Composites |
Common exam errors
- Saying diamond conducts — it does NOT (all electrons bonded).
- Confusing graphene (single layer) with graphite (stacked layers).
- Saying fullerenes have high melting points because they are carbon — they are small molecules with relatively low melting points.
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