Question

# When heated in air, the alkali metals form various oxides. Mention the oxides formed by Li, Na and K.

Solution

## The reactivity of alkali metals towards oxygen increases on moving down the group with the increase in atomic size. Thus , Li forms only lithium oxide  Li2O  but the sodium forms mainly sodium peroxide Na2O2  along with a small amount of sodium oxide while potassium forms only potassium superoxide (KO2)  4Li + O2△−→ 2Li2O6Na + 2 O2△−→ Na2O2Sodium peroxiode  (major) + 2 Na2O  Monoxide(minor)K+O2△−→KO2Potessiumsuper oxide+K2O2Peroxide+K2(O)Monoxide The superoxede,O−2 ion is stable only in presence of large cations such as K, Rb etc.

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