Explain why graphene is an electrical conductor, whilst poly(ethene) is an electrical insulator, despite both materials consisting predominantly of carbon and hydrogen atoms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Graphene is a single layer of carbon atoms arranged in a planar hexagonal lattice. Poly(ethene) is a polymer formed by addition polymerisation of ethene monomers.
Model answer (4 marks)
In graphene each carbon atom is sp²‑hybridised, forming three σ bonds with neighbours and leaving one electron in an unhybridised p orbital. These p orbitals overlap across the sheet, creating a delocalised π‑electron system that can move freely and carry charge, so graphene conducts electricity.
In poly(ethene) every carbon is sp³‑hybridised; all four valence electrons are used in σ bonds to other carbons or hydrogens. There are no π electrons or delocalised electrons, so no charge carriers are available and the polymer is an insulator.
In poly(ethene) every carbon is sp³‑hybridised; all four valence electrons are used in σ bonds to other carbons or hydrogens. There are no π electrons or delocalised electrons, so no charge carriers are available and the polymer is an insulator.
Examiner tips
- Use the terms ‘sp²’, ‘σ bonds’, ‘p orbital’, ‘delocalised π system’ for graphene; mention ‘sp³’ and ‘σ bonds only’ for poly(ethene).
- Explain that delocalised electrons allow charge transport, while their absence means no conduction.
Common mistakes
- Confusing sp² with sp³ for graphene; or saying both have delocalised electrons. Saying poly(ethene) is conductive because it contains carbon.
Mark scheme (4 marks)
- In graphene, each carbon atom forms three sigma bonds leaving one electron in an unhybridised p orbital (or: each carbon has a non-bonding/delocalised electron).
- These p electrons overlap across the entire graphene layer to form a delocalised system of electrons that can move freely and carry charge.
- In poly(ethene), all four valence electrons of each carbon are used in sigma (single covalent) bonds to hydrogen or adjacent carbon atoms.
- Because there are no delocalised electrons in poly(ethene), no charge carriers are available and the material cannot conduct electricity.
Key terms in this question
electrical conductor · insulator · poly(ethene) · graphene
Related
- All IB DP Chemistry Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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