Question

The stability fo peroxide and superoxide of alkali metals increase as we go down to group. Explain giving reason.

Answer 1

The stability of peroxide or superoxide increases as the size of metal ion increases i.e.$K{O}_2<Rb{O}_2<Cs{O}_2$ The reactivity fo alkali metals toward oxygen to form different oxides is due to strong positive field around each alkali metal cation. $L{i}^{+}$ is the smallest, it does not allow $O^{2-}$ ion to react with $O_2$ further. $N{a}^{+}$ is larger than Li, its positive field is weaker than $L{i}^{+}$ It cannot prevent the conversion of $O^{2-}$ into $O_2^{2-}$

The largest $K^{+}$ , $R{b}^{+}$ and $C{s}^{+}$ ions permit $O_2^{2-}$ ion to react with $O_2$ forming superxide ion $O_2^{-}$ .
$\underset{Oxide}{O_2^{2-}}\stackrel{\frac{1}{2}{O}_2}{\to }\underset{Peroxide}{O^{2-}}\stackrel{O_2}{\to }\underset{Superoxide}{2O_2^{-}}$
Moreover, Increased stability of the peroxide or superoxide with increase in the size of metal ion is due to the stabilisation of large sanions by larger cations through lattice energy effect.