Carbon: graphite and diamond
Chemistry · Key Stage 2 · The School
Two very different materials, one substance
Graphite is soft and dark. It is the material inside a pencil. Diamond is very hard and sparkly. It can cut other hard things. The two seem totally unrelated. But both are made of the exact same stuff: carbon.
Same tiny bits, different pattern
Carbon is made of tiny bits called atoms. In diamond, the atoms lock into a strong pattern. That is why diamond is so hard. In graphite, the atoms sit in flat sheets. The sheets slide over each other. That is why graphite is soft.
What each one is used for
Diamond is used in drill tips. It is used in cutting tools too. Nothing soft would survive that job. Graphite is used in pencils. It is soft, so it slides and leaves a mark. It is also used to help machine parts slide smoothly past each other.
Suppose a lab has two samples of pure carbon, A and B, but the labels have fallen off. The lab knows each one is graphite or diamond. Test 1: scratch each sample with the other. B scratches A, but A cannot scratch B. So B is the harder one. The Mohs scale ranks hardness from 1 to 10. Graphite scores 1 to 2 and diamond scores 10. Diamond is the harder of the two, so B should be diamond. Test 2: put each sample in a circuit with a battery and a meter. Graphite carries electricity less well than metal, so a bulb might stay dim. A meter shows even a small flow of electricity. It shows a flow for A and none for B. Graphite carries electricity, and most diamonds do not. Both tests agree: A is graphite and B is diamond. Both are carbon, so the difference comes from the pattern of atoms.