Fullerenes are molecules of carbon atoms with hollow shapes. One well-known fullerene is C₆₀. Explain why C₆₀ has a much lower melting point than diamond, even though both substances are made entirely of carbon atoms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
C₆₀ is a fullerene made of 60 carbon atoms arranged in a hollow sphere. Diamond is a giant covalent structure in which each carbon atom forms four covalent bonds with four other carbon atoms.
Model answer (5 marks)
Diamond is a giant covalent structure; every C atom is bonded to four others by very strong covalent bonds, so a large amount of energy is required to break the network and melt the material.
C₆₀ is a discrete molecule; the 60 C atoms are bonded together only within each molecule, and the molecules are held together in the solid by weak intermolecular forces.
Because only the weak intermolecular forces must be overcome to melt C₆₀, far less energy is needed, giving it a much lower melting point than diamond.
C₆₀ is a discrete molecule; the 60 C atoms are bonded together only within each molecule, and the molecules are held together in the solid by weak intermolecular forces.
Because only the weak intermolecular forces must be overcome to melt C₆₀, far less energy is needed, giving it a much lower melting point than diamond.
Examiner tips
- Use the word ‘giant covalent structure’ for diamond and ‘discrete molecules’ for C₆₀. Mention strong covalent bonds vs weak intermolecular forces. Show the link between bond strength and energy required to melt.
Common mistakes
- Confusing the type of bonds (covalent vs intermolecular) or saying both are covalent. Failing to explain that C₆₀ is a separate molecule rather than a network. Using vague terms like ‘strong’ or ‘weak’ without linking to energy required.
Mark scheme (5 marks)
- Diamond is a giant covalent structure with many strong covalent bonds throughout the whole structure
- A large amount of energy is needed to break the many strong covalent bonds in diamond, so it has a very high melting point
- C₆₀ consists of individual/separate molecules (not a giant structure)
- The forces between C₆₀ molecules are intermolecular forces (not covalent bonds)
- Less energy is needed to overcome the weak intermolecular forces between C₆₀ molecules, so it has a lower melting point
Key terms in this question
Related
- All OCR A-Level Chemistry B: Salters (H433) revision notes →
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