Graphite and diamond are both giant covalent structures made entirely of carbon atoms, yet they have very different physical properties. Explain why graphite can conduct electricity but diamond cannot.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Graphite is used as an electrode material in batteries and electrolysis cells, whilst diamond is used as an electrical insulator in cutting tools and heat sinks.
Model answer (4 marks)
In graphite each carbon atom forms three covalent bonds with three other carbons, leaving one electron per atom that is not involved in bonding. This electron is delocalised over the layers and can move freely, carrying charge and allowing electrical current to flow.
In diamond each carbon atom forms four covalent bonds with four other carbons, using all its electrons in bonding. There are no delocalised electrons, so diamond cannot conduct electricity.
In diamond each carbon atom forms four covalent bonds with four other carbons, using all its electrons in bonding. There are no delocalised electrons, so diamond cannot conduct electricity.
Examiner tips
- Show the difference in bonding (3 vs 4 bonds) and link to free electrons
- Explain how delocalised electrons enable conduction
- Keep answer concise and use correct terminology
Common mistakes
- Confusing graphite with diamond or vice versa
- Failing to mention delocalised electrons
- Using vague terms like "more electrons" instead of "free electrons"
Mark scheme (4 marks)
- In graphite, each carbon atom forms three covalent bonds (with three other carbon atoms), leaving one electron per carbon atom not used in bonding.
- In graphite, the remaining electron per carbon atom is delocalised (free to move) and can carry charge / carry an electric current.
- In diamond, each carbon atom forms four covalent bonds with four other carbon atoms, so all electrons are used in bonding.
- Because diamond has no delocalised (free) electrons, it cannot conduct electricity.
Key terms in this question
giant covalent structure · graphite · diamond
Related
- All OCR GCSE Chemistry A: Gateway Science (J248) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →