Explaining the increase in reactivity
2 marks · EasyExplain why the outer electron in a caesium atom is lost more easily than the outer electron in a lithium atom.
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The outer electron in caesium is much further from the nucleus than in lithium because caesium has more electron shells. This means the attractive force from the nucleus is weaker, so the outer electron is lost more easily.
Also accept: Caesium has more electron shells, so its outer electron is further away and less strongly held; More shells in caesium, weaker force holding the outer electron
Common mistakes: Lithium is more reactive than caesium; The number of protons only
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Marking points
M1 · 1 mark · Mentions greater number of shells/more distant outer electron for caesium compared to lithium.
A1 · 1 mark · Explains this reduces the force of attraction so the outer electron is lost more easily.
Worked solution
Caesium has more electron shells than lithium, so its outer electron is much further from the nucleus and is less strongly attracted. This means caesium's outer electron is lost more easily.