Metals and non-metals in the periodic table
4 marks · NormalThis question is about group trends in the periodic table.
Describe how the electronic configurations of chlorine and bromine are similar.
Group 7 elements react with hydrogen to form compounds such as hydrogen chloride and hydrogen bromide. State one similarity in the formulae of these compounds.
Explain why elements in the same group have similar chemical properties.
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(a) Both have 7 electrons in their outer shell
(b) Both compounds have the formula HX, where X is the halogen (e.g. HCl, HBr)
(c) Because elements in the same group have the same number of electrons in their outer shell, so they react in similar ways.
Common mistakes: Stating atoms have same number of electrons without specifying outer shell
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Marking points
B1 (a) · 1 mark · States 'both have 7 electrons in their outer shell' or similar answer
B1 (b) · 1 mark · States 'both are of form HX' or 'hydrogen + halogen' or gives two correct examples
M1 (c) · 1 mark · Identifies 'same number of electrons in the outer shell'
A1 (c) · 1 mark · States that this leads to similar reactions/chemical properties
Worked solution
a) Chlorine and bromine both have 7 electrons in their outer shell.
b) The formulae are similar: both are of the form HX (e.g., HCl, HBr).
c) Elements in the same group have the same number of electrons in their outer shell, so they have similar chemical properties; they react in similar ways.