Write a short note on the reactivity of alkali metals towards air.

Explanation

The alkali metals forms their oxides in presence of dry air and tarnished.
These oxides reacts with moisture to form hydroxides.
They burn vigorously in oxygen and forms oxides.
(i) Lithium forms Lithium monoxide.
(ii) Sodium forms monoxide with limited supply of oxygen and peroxide with excess of oxygen
(iii) Other metals of this group forms super oxides. The super oxide ion `(O_2^-)` is stable only in presence of large cations.
Reactions:
`4Li+O_2 to 2Li_2O`
`4Na+O_2` (limited) `to 2Na_2O`
`2Na +O_2` (Excess) `to Na_2O_2`
`K+O_2` (Excess) `to KO_2`
Lithium shows a different character. It reacts directly with nitrogen of air and forms `Li_2N` (lithium nitride).