Covalent substances can be simple molecular covalent or giant covalent. The arrangement of carbon atoms in diamond, graphene and a fullerene (C60). Consider these three substances. Explain, in terms of their structures and bonding, their relative melting points, strengths and abilities to conduct electricity – 9012

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1. In all three structures, carbon atoms are bonded by strong single covalent bonds where electrons are shared.

   In diamond, each carbon atom is bonded to four other carbon atoms, forming a giant covalent lattice. In graphene, each carbon is bonded to three others, and it also has a giant covalent structure. Fullerene is made of molecules, not a giant lattice.

   Diamond and graphene have many strong covalent bonds that need a lot of energy to break, so they have very high melting or sublimation points. Fullerene has weak forces between molecules, so less energy is needed to separate them. That’s why fullerene has the lowest melting point.

   Diamond does not conduct electricity because there are no free electrons. In graphene and fullerene, each carbon has one free (delocalised) electron. Graphene has delocalised electrons that move freely, so it conducts electricity well. Fullerene only conducts on the surface of the molecule and doesn’t let electrons move easily between molecules, so it is a poor conductor or semiconductor.

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