Explaining the increase in reactivity
2 marks · NormalExplain why lithium reacts more slowly than sodium when added to water.
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Lithium has fewer electron shells than sodium, so its outer electron is closer to the nucleus and is more strongly attracted. This makes it harder to lose the electron, so lithium reacts more slowly.
Also accept: Lithium's outer electron is closer to the nucleus, so it is harder to remove.
Common mistakes: Just saying 'because lithium is less reactive' without explanation
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Marking points
B1 · 1 mark · States lithium has fewer shells/outer electron is closer to the nucleus than sodium.
B2 · 1 mark · Explains the outer electron is more strongly attracted, so harder to lose and reaction is slower.
Worked solution
Lithium has fewer electron shells than sodium, so its outer electron is closer to the nucleus and more strongly attracted.
It is therefore harder to lose the electron, so lithium reacts more slowly than sodium.