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

Explanation

The alkali metals when exposed to air reacts with oxygen, moisture and carbondioxide forming oxide, hydroxide and carbonate. So they immediately tarnish in air.
eg: `4Na + O_(2) to 2Na_(2)O`
`Na_(2)O + H_(2)O to 2NaOH`
`2NaOH + CO_(2) to Na_(2)CO_(3) + H_(2)O`
Alkali metals burn in air forming oxide. Lithium forms only monoxide.
`4Li+O_(2) to 2Li_(2)O`
Sodium forms monoxide in limited supply of air but forms peroxide in excess of oxygen.
`4Na+O_(2) to 2 Na_(2)O_(2)`
`2Na + O_(2) to Na_(2)O_(2)`
Other alkali metals form superoxides
`M + O_(2) ("excess") to MO_(2)(M = k , Rb, Cs)`.