Giant covalent structures
3 marks · NormalA student connects graphite, diamond and C60 fullerene electrodes into identical electric circuits. The student measures the current in each case:
| Substance | Current/mA |
|---|---|
| Diamond | 0.0 |
| Graphite | 15.0 |
| C60 fullerene | 0.0 |
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Only graphite conducts electricity because it has delocalised electrons free to move and carry current. Diamond and C60 fullerene do not conduct electricity because diamond has no free electrons, and the electrons in C60 are trapped within each molecule and cannot move between molecules.
Also accept: Graphite is the only one that conducts electricity due to delocalised electrons between layers. Diamond's electrons are fixed in covalent bonds; C60's electrons cannot move across molecules.
Common mistakes: saying C60 conducts electricity because it has three bonds per carbon
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Marking points
M1 · 1 mark · States graphite conducts electricity, not diamond or C60.
M2 · 1 mark · Explains graphite conducts due to mobile/delocalised electrons between layers.
A1 · 1 mark · Explains that diamond has no delocalised electrons, C60's electrons are not free to move between molecules.
Worked solution
Graphite conducts electricity (current = 15.0 mA) because it contains delocalised electrons between layers that move freely and carry electrical charge. Diamond (current = 0.0 mA) does not conduct: all electrons are involved in strong covalent bonds, so none can move. C60 fullerene (current = 0.0 mA) also does not conduct, even though each carbon forms three bonds, because its remaining electrons can only move within each C60 molecule and are not free between molecules to carry current.