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‘ The stability of peroxides & super oxides increases with the size of the metal ion . This is due to the stabilization of large anions by large cations through lattice enthalpy‘ Expalin the statement.

The stability of peroxides & super oxides increases with the size of the metal ion . This is due to the stabilization of large anions by large cations through lattice enthalpy‘
Expalin the statement.

Grade:11

1 Answers

Aarti Gupta
askIITians Faculty 300 Points
9 years ago
Alkali metals when burnt in air form different types of oxides.For ex-Li forms normal oxide(Li2O),sodium form peroxide(Na2O2)and potassium,rubidium,and cesium form superoxides of general formula MO2.
It is found that stability of peroxide or superoxide increases as the size of the metal ion increases which is due to the stabilization of larger anions by larger cation through higher lattice energies.As we movedown the group from Li+ to Cs+ we know that the size of the cations increases.Li+ is the smallest cation with strong positive field around it. Hence it combines with small anion called oxide ion (O-2) with strong negative field and form Lithium oxide.On the other hand Na+ ion is bigger than Li+ ion with less positive field around it combines with peroxide ion with less negative field and form sodium peroxide.
Now in case of K+, Rb+ and Cs+ ions which are bigger in size there is less positive field around them. Hence they can stabilize the bigger superoxide ion (O2-) with less negative field and form super oxides.

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