Question

Arrange the following in increasing order of stability: oxides, peroxides and superoxides (of Alkali metals)

Answer 1

Dear Student,
Answer is oxide < peroxide < superoxide

Solution:-

Oxides: Stability decreases down the group with lithium oxide the most stable.
Peroxides: Increases and then decreases as we go from top to bottom in the group with sodium peroxide having the maximum stability.
Superoxide: Stability increases down the group. Superoxides of K, Rb and Cs are most stable.

Larger cations are stabilized by larger anions due to higher lattice energies.The anion sizes in increasing order are oxide < peroxide < superoxide, so lithium forms the most stable oxide, sodium the most stable peroxide and superoxide is the most stable form for the rest.
The high charge density of lithium ion attracts the negative charge so strongly that it does not allow the oxide ion to take up another oxygen atom to form the peroxide ion. Sodium forms a peroxide as it forms a comparatively weaker positive field around it. K, Rb and Cs have weaker positive field around their cations and thus the oxide ion can take up two more oxygen atoms to form the superoxide ion.​