Giant covalent structures
4 marks · NormalDiamond is a non-conductor of electricity and is very hard, while graphite is soft but conducts electricity.
Explain, in terms of bonding and structure, why diamond does not conduct electricity.
Explain, using bonding and the arrangement of atoms, why graphite is soft.
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(a) Diamond does not conduct electricity because all electrons are used in strong covalent bonds and there are no free electrons to move.
(b) Graphite is soft because, while atoms are held together strongly in layers, the forces between layers are weak, so layers can easily slide over each other.
Common mistakes: missing delocalised electrons; not relating softness to structure
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Marking points
M1 (a) · 1 mark · Explains all electrons in diamond are bonded (used in covalent bonds).
A1 (a) · 1 mark · Correctly states no free/delocalised electrons, so cannot carry current.
M2 (b) · 1 mark · Explains graphite has weak forces between layers.
A2 (b) · 1 mark · States that layers slide easily, making it soft.
Worked solution
a) Diamond does not conduct electricity because all the electrons are tightly held in covalent bonds between carbon atoms. There are no free (delocalised) electrons or ions to carry charge.
b) Graphite is soft because its structure is made of layers. The atoms in each layer are joined by strong covalent bonds, but the forces between the layers are weak. This allows the layers to slide over each other easily, so graphite is soft.