Explaining the increase in reactivity
3 marks · NormalWhen potassium and sodium are each added separately to water, potassium reacts much more vigorously than sodium.
Use knowledge of their atomic structures to explain fully why potassium is more reactive than sodium.
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Potassium's atom is larger than sodium's and has more electron shells, so its outer electron is further from the nucleus. This means it is less strongly attracted to the nucleus and is more easily lost, so potassium is more reactive.
Also accept: Potassium's outer electron is in a shell farther from the nucleus than sodium's, so it is held less tightly and lost more easily, making potassium more reactive.
Common mistakes: Not mentioning electron shells/distance; Giving only experimental observations
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Marking points
B1 · 1 mark · States potassium has more shells/larger atomic radius than sodium.
B2 · 1 mark · Outer electron further from nucleus/less strongly attracted.
B3 · 1 mark · Therefore, the outer electron is more easily lost, so potassium is more reactive.
Worked solution
Potassium has more electron shells than sodium, so its outer electron is further from the nucleus.
This means the outer electron is less strongly attracted to the positive nucleus.
It is more easily lost, so potassium reacts more readily than sodium.