Explain why buckminsterfullerene (C₆₀) has a significantly lower melting point than diamond, despite both being allotropes of carbon.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Diamond has a giant covalent (network) structure in which every carbon atom is covalently bonded to four others throughout the lattice.
Melting diamond requires breaking many strong covalent C–C bonds throughout the entire lattice, which requires a very large amount of energy.
Buckminsterfullerene consists of discrete, individual C₆₀ molecules held together in the solid state by weak London (dispersion) forces.
Only these weak intermolecular forces need to be overcome to melt C₆₀, so relatively little energy is required, giving a much lower melting point.
Melting diamond requires breaking many strong covalent C–C bonds throughout the entire lattice, which requires a very large amount of energy.
Buckminsterfullerene consists of discrete, individual C₆₀ molecules held together in the solid state by weak London (dispersion) forces.
Only these weak intermolecular forces need to be overcome to melt C₆₀, so relatively little energy is required, giving a much lower melting point.
Examiner tips
- Use the term ‘giant covalent (network) structure’ for diamond. Explain that melting requires breaking many C–C bonds. Mention that C₆₀ is held by London forces. Show that only weak forces are broken, so energy is low.
Common mistakes
- Confusing C₆₀ as a network solid. Forgetting to mention London forces. Over‑emphasising the size of C₆₀ instead of bond strength.
Mark scheme (4 marks)
- Diamond has a giant covalent (network) structure in which every carbon atom is covalently bonded to four others throughout the lattice.
- Melting diamond requires breaking many strong covalent C–C bonds throughout the entire lattice, which requires a very large amount of energy.
- Buckminsterfullerene consists of discrete, individual C₆₀ molecules held together in the solid state by weak London (dispersion) forces.
- Only these weak intermolecular forces need to be overcome to melt C₆₀, so relatively little energy is required, giving a much lower melting point.
Key terms in this question
allotrope · buckminsterfullerene
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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