What are allotropes? Compare diamond and graphite in structure and properties, and give two uses of each.

1. 1 · Define. Allotropes are different forms of the same element in the same physical state. Carbon has three: diamond, graphite and fullerenes.
2. 2 · Structure. Diamond: each C is bonded to 4 others in a 3D tetrahedral network. Graphite: each C is bonded to 3 others in layers.
3. 3 · Draw both. Draw the tetrahedral unit of diamond, and two layers of hexagons for graphite with weak forces between them.
4. 4 · Properties.
   • Diamond: hardest, does not conduct electricity, density 3.51 g cm⁻³
   • Graphite: soft and slippery, conducts electricity, density 2.2 g cm⁻³
5. 5 · Uses.
   • Diamond: cutting glass, drilling rocks, jewellery
   • Graphite: pencil leads, electrodes, dry lubricant
6. 6 · Real life. A glass cutter has a diamond tip, and your pencil has graphite.
7. 7 · Close in one line. So the same atoms, arranged differently, give very different properties.

Scoring tip: Link each use to the property behind it: hard, so it cuts; slippery, so it lubricates. That link earns the mark.