The reactivity of Group I metals with water increases down the group. The diagram shows three beakers of water with lithium, sodium and potassium added. Whi...
Question 1 Report
The reactivity of Group I metals with water increases down the group. The diagram shows three beakers of water with lithium, sodium and potassium added. Which beaker, labelled by metal, shows the most violent reaction?
Answer Details
Group I reactivity increases down the group because the outer electron is further from the nucleus and better shielded, so it is lost more easily. Losing that electron is exactly what the reaction with water requires:
\[ 2\text{M} + 2\text{H}_2\text{O} \rightarrow 2\text{MOH} + \text{H}_2 \]
Of the three beakers, potassium is the lowest of these metals in Group I, so it loses its outer electron most readily and reacts most violently. It melts, skims the surface and the hydrogen ignites with a lilac flame. Sodium melts and fizzes rapidly but usually does not ignite, and lithium fizzes steadily without melting.
Do not assume the metal with the smallest atoms is the most reactive; for Group I the trend runs the other way.
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