Allotropes of carbon
Carbon is unique in forming several allotropes — different structural forms of the same element. The five GCSE-relevant ones are diamond, graphite, graphene, fullerenes (incl. buckminsterfullerene C₆₀), and carbon nanotubes.
Diamond
- Each carbon bonded to 4 others in a tetrahedral 3D lattice — giant covalent.
- All four outer electrons used in bonding → no delocalised electrons → does NOT conduct.
- Hard, very high m.p. — many strong covalent bonds throughout.
- Used in cutting tools, jewellery.
Graphite
- Each carbon bonded to 3 others in flat hexagonal layers (rings of 6).
- Each carbon's 4th outer electron is delocalised within the layer.
- Layers held to each other by weak intermolecular forces.
- Soft / slippery — layers slide easily.
- Conducts electricity along layers — delocalised electrons move freely.
- High m.p. — covalent bonds within layers must be broken to vaporise.
- Used as electrodes, lubricant, pencil lead.
Graphene
A single layer of graphite, just one atom thick.
- Each carbon bonded to 3 others in a hexagonal sheet.
- Delocalised electrons → excellent conductor of electricity and heat.
- Extremely strong for its mass — strong covalent bonds, all carrying load efficiently.
- Almost transparent.
- Uses: future high-strength composites, transparent electrodes, electronics.
Fullerenes
Hollow shapes (cages, balls, tubes) made of carbon, generally with hexagons (like graphite) and pentagons (which are needed to close the curved surface).
Buckminsterfullerene (C₆₀)
- 60 carbon atoms in a sphere — like a football pattern (20 hexagons + 12 pentagons).
- Used in: drug delivery, lubricants (rolls like ball bearings), catalysis.
Carbon nanotubes
- Cylinders of graphene-like carbon.
- High length-to-diameter ratio.
- Strong, conduct electricity, conduct heat.
- Uses: nanotechnology, electronics, composites for sports gear and aerospace.
Comparing properties
| Allotrope | Conducts? | Hardness | Bonds per C | Notes |
|---|---|---|---|---|
| Diamond | No | Very hard | 4 | Cutting, jewellery |
| Graphite | Yes (along layers) | Soft | 3 + 1 delocalised | Pencils, electrodes |
| Graphene | Yes | Strong | 3 + 1 delocalised | One-atom-thick sheet |
| C₆₀ | Slight | Soft | 3 + 1 (curved) | Drug delivery |
| Nanotubes | Yes | Very strong | 3 + 1 delocalised | Composites |
✦Worked example
Why is graphene a good electrical conductor?
- Each C atom in graphene bonds to 3 others B1
- 4th electron of each C is delocalised across the sheet B1
- These delocalised electrons can move and carry charge B1
⚠Common mistakes
- Calling fullerenes "covalent compounds" — they're allotropes (forms of an element), not compounds.
- Saying graphene is a 2D molecule. It's a single covalent layer — a giant covalent structure but one atom thick.
- Drawing pentagons in flat graphite. Pentagons appear in fullerenes (curved); graphite is all hexagons.
- Confusing nanotubes with simple molecules. Nanotubes are giant — long covalent networks.
Links
Builds on C2.3 (covalent) and C2.6 (linking properties). Connects to C2.8 (nanoparticles).
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