Why is it that on being heated in excess supply of air, K, Rb and Cs form super oxides in preference to oxides?

Why is it that on being heated in excess supply of air, K, Rb and Cs f

1.	Why is it that on being heated in excess supply of air, K, Rb and Cs form super oxides in preference to oxides?
Answer» ND Cs are alkali metals and are in 4th, 5th and 6TH group of the periodic table. We know that the size of the metal atom INCREASES as we go down the group. All the alkali metals form normal oxides of the TYPE in limited supply of air. But when heated in adequate or excess availability of air, normal oxide, peroxide or super oxides are formed depending upon the group to which the alkali metal BELONGS to. 2nd group (Li) → normal oxide 3nd group (Na) → peroxide oxide 4th, 5th and 6th groups (K, Rb and Cs) → super oxide . This is because the stability of normal oxide, peroxide and super oxide increases down the group. Larger cation stabilizes larger anion. Super oxide ions are larger than peroxide ions or normal oxide ions due to lattice energy considerations.