Down group I from lithium to caesium, the reactivity of the metals
Correct answer: D. increases, because the outer electron is further from the nucleus and more easily lost
- A. decreases, because atomic radius increases
- B. stays constant
- C. decreases, because ionisation energy falls
- D. increases, because the outer electron is further from the nucleus and more easily lost
Explanation
Each element down the group has an extra shell, so the single outer electron is further from the nucleus and better shielded, ionisation energy falls and the metal loses that electron more readily. This is why potassium ignites the hydrogen it releases from water while lithium merely fizzes. In the halogens the same reasoning gives the opposite trend, since there reactivity depends on gaining an electron.
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About Reactions of Group I Elements
Group I elements have one valence electron, so their reactivity increases down the group as ionisation energy decreases. Their reactions with water, oxygen, hydrogen and halogens produce hydroxides, oxides, hydrides and halides, while the behaviour of lithium differs from the heavier metals because of its small ionic size.
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