Giant covalent structures
5 marks · HardThe three allotropes of carbon—diamond, graphite, and C60 fullerene—have different abilities to conduct electricity.
State which, if any, of these allotropes can conduct electricity.
For each allotrope, explain your answer by referring to their bonding and the movement of electrons.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Only graphite conducts electricity.
(b) — · must show Diamond: all electrons tightly held, no conduction; Graphite: has delocalised electrons, conducts; C60: electrons cannot move between molecules, does not conduct.
Common mistakes: Omitting mention of delocalised electrons in graphite; incorrect statement that C60 fullerene conducts electricity as well as graphite; confusion over whether diamond has free electrons.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that only graphite conducts electricity.
B2 (b) · 1 mark · Explains that diamond does not conduct because all electrons are held in covalent bonds (no free electrons).
B3 (b) · 1 mark · Explains graphite conducts due to delocalised electrons that can move throughout the layers.
B4 (b) · 1 mark · Explains C60 fullerene does not conduct because electrons cannot move from one C60 molecule to another.
B5 (b) · 1 mark · Uses correct references to movement or delocalisation of electrons for any two of the allotropes.
Worked solution
a) Only graphite can conduct electricity.
b) In diamond, each carbon atom bonds to four others using all its outer electrons—there are no free electrons to move, so diamond cannot conduct electricity. In graphite, each carbon atom forms three bonds; the fourth electron is delocalised and free to move through the layers, so graphite conducts electricity. In C60 fullerene, the delocalised electrons are confined within each molecule and cannot move from molecule to molecule, so C60 does not conduct electricity.