Explain why graphene is an excellent electrical conductor, whilst diamond is a poor electrical conductor, despite both being allotropes of carbon.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
In graphene each C atom is sp²‑hybridised and makes three σ bonds, leaving one electron in a p orbital that is not hybridised. These p electrons overlap laterally across the sheet, forming a delocalised π system – a sea of free electrons that can move easily and carry charge.
In diamond each C atom is sp³‑hybridised and forms four σ bonds, using all four valence electrons. There are no electrons left to delocalise, so no mobile charge carriers are present.
Because graphene has delocalised electrons that can move freely, it is an excellent conductor. Diamond, lacking mobile charge carriers, is a poor conductor.
In diamond each C atom is sp³‑hybridised and forms four σ bonds, using all four valence electrons. There are no electrons left to delocalise, so no mobile charge carriers are present.
Because graphene has delocalised electrons that can move freely, it is an excellent conductor. Diamond, lacking mobile charge carriers, is a poor conductor.
Examiner tips
- Use the terms sp², sp³, σ bonds, delocalised π system, mobile charge carriers
- Explain the difference in electron availability to justify conductivity
- Keep answer concise and directly linked to the marks
Common mistakes
- Confusing sp² with sp³ for graphene
- Claiming diamond has free electrons without justification
- Using vague terms like ‘good conductor’ without explaining electron delocalisation
Mark scheme (4 marks)
- In graphene, each carbon atom forms three sigma bonds (sp2 hybridised), leaving one electron in an unhybridised p orbital per carbon atom.
- These p electrons overlap laterally across the entire sheet to form a delocalised pi system / sea of delocalised electrons that are free to move and carry charge.
- In diamond, each carbon atom forms four sigma bonds (sp3 hybridised) using all four valence electrons, leaving no electrons available for conduction.
- Because diamond has no mobile charge carriers (no free electrons or ions), it cannot conduct electricity, whereas graphene's delocalised electrons act as mobile charge carriers, making it highly conductive.
Key terms in this question
Related
- All IB DP Chemistry Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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