Covalent Bonding
6 marks · NormalThis question tests your understanding of covalent bonding and how it affects the properties of substances.
Calculate the total number of covalent bonds formed in a molecule of ethene (C2H4). Show your working.
The table shows the electrical conductivity of three substances:
| Substance | Electrical conductivity |
|---|---|
| Diamond | Does not conduct |
| Graphite | Conducts |
| C60 fullerene | Does not conduct |
Explain, using their structure and bonding, why graphite conducts electricity but diamond and C60 fullerene do not.
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) 5 covalent bonds. · must show C=C double bond (1), C-H bonds (4)
(b) Graphite: Each carbon atom is bonded to three others in layers, with one electron per atom delocalised and free to move, so graphite conducts electricity. Diamond: Each carbon is bonded to four others, no delocalised electrons, so it does not conduct. C60 fullerene: although each carbon forms three bonds, delocalised electrons cannot move between molecules, so C60 does not conduct electricity. · must show graphite: free/delocalised electrons, diamond: no free electrons, C60: electrons not free between molecules
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Marking points
M1 (a) · 1 mark · Identifies the correct types of bonds: 1 C=C, 4 C-H.
A1 (a) · 1 mark · Correctly totals 5 covalent bonds.
E1 (b) · 1 mark · Graphite: Describes delocalised electrons are present and can move.
E2 (b) · 1 mark · Graphite: Correct link between delocalised electrons and conduction.
E3 (b) · 1 mark · Diamond: Identifies no delocalised electrons or all electrons bonded.
E4 (b) · 1 mark · C60: States electrons cannot move between molecules.
Worked solution
a) In ethene (C2H4), each C is bonded to two H and the other C. There is a double bond between the two C atoms, so C=C (1), plus 4 C-H bonds. Total = 5 covalent bonds.
b) Graphite: each carbon is joined to three others with one delocalised electron per atom that moves throughout the layers, allowing conduction. Diamond: all four electrons per carbon form covalent bonds, so none are free to move; no conduction. C60 fullerene: each carbon forms three bonds, but the spare electron is trapped inside the molecule and not free to move between molecules, so C60 does not conduct.