Lithium forms monoxide with oxygen whereas sodium forms peroxide with oxygen. Why?

Explanation

The fact that a small cation can stabilize a small anion and a large cation can stabilize a large anion explains the formation and stability of the oxides
(ii) The size of Lition is very small and it has a strong positive field around it. It can combine with only small anion, 02-ion, resulting in the formation of monoxide Li,O.
(iii) The Nation is a larger cation and has a weak positive field around it and can stabilize a bigger peroxide ion, `O_(2)^(2)`or `[-O-O-]^(2-)` resulting in the formation of peroxide `Na_(2)O_(2)`