Displayed formulae
5 marks · HardAnswer the following questions about typical bonding in displayed formulae of organic compounds.
State the typical number of bonds formed by a carbon atom in a displayed formula.
State the typical number of bonds formed by a hydrogen atom in a displayed formula.
State the typical number of bonds formed by an oxygen atom in a displayed formula.
State the typical number of bonds formed by a halogen atom (such as chlorine) in a displayed formula.
Explain why a carbon atom in organic molecules always forms this number of bonds.
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(a) 4
(b) 1
(c) 2
(d) 1
(e) Carbon has four electrons in its outer shell and needs to form four covalent bonds to achieve a full outer shell (octet), so it always forms four bonds in its compounds.
Common mistakes: Incorrect bond numbers, e.g. oxygen as one bond.; Confusing halogens with oxygen.; Not clearly linking carbon's four bonds to its electrons or valency.
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Marking points
B1 (a) · 1 mark · States carbon forms 4 bonds.
B2 (b) · 1 mark · States hydrogen forms 1 bond.
B3 (c) · 1 mark · States oxygen forms 2 bonds.
B4 (d) · 1 mark · States halogen forms 1 bond.
M1 (e) · 1 mark · Explains that carbon forms 4 bonds because it has 4 outer electrons and needs 4 more to fill its outer shell.
Worked solution
a) 4
b) 1
c) 2
d) 1
e) Carbon has four electrons in its outer shell and forms four covalent bonds to complete its octet (eight electrons). This gives it a stable electronic arrangement.