Rubidium and caesium
3 marks · NormalExplain, in terms of atomic structure, why potassium is more reactive than lithium.
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Common mistakes: Not mentioning electron shells; Ignoring the attraction between electron and nucleus; Stating only that potassium is 'further down the group'
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Marking points
B1 · 1 mark · Potassium atom has more electron shells than lithium
B2 · 1 mark · The outer electron in potassium is further from the nucleus
B3 · 1 mark · The outer electron is less strongly attracted to the nucleus and lost more easily
Worked solution
Potassium atoms have more electron shells than lithium atoms, so their outer electrons are further from the nucleus. This means the outer electron in potassium is less strongly attracted to the nucleus and is lost more easily than in lithium, making potassium more reactive.