Explain why diamond has a very high melting point and does not conduct electricity.

Edexcel GCSE Chemistry (1CH0) — 1.6 Covalent bonding · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Diamond is a form of carbon used in cutting tools and jewellery. It is one of the hardest known substances and has an extremely high melting point.

Model answer (4 marks)

Diamond has a giant covalent structure.
Each carbon atom forms four strong covalent bonds to other carbon atoms.
A very large amount of energy is needed to break these many strong covalent bonds, hence the high melting point.
Diamond does not conduct electricity because it has no free electrons (or ions) to carry charge.

Examiner tips

Use the term ‘giant covalent structure’ early. Explain that each C atom is tetrahedrally bonded. Show that breaking all bonds requires a lot of energy. Mention lack of free charge carriers for conductivity.

Common mistakes

Confusing diamond with graphite and saying it conducts. Forgetting to mention the tetrahedral bonding. Saying ‘high melting point’ without linking to bond strength.

Mark scheme (4 marks)

Diamond has a giant covalent structure
Each carbon atom forms four strong covalent bonds to other carbon atoms
A very large amount of energy is needed to break these many strong covalent bonds, hence the high melting point
Diamond does not conduct electricity because it has no free electrons (or ions) to carry charge

Key terms in this question

melting point