Page 2 - Microsoft Word - Module-1

 Alkali metals are used in photoelectric cells due to

low ionization enthalpy.

TRENDS IN CHEMICAL PROPERTIES:

 Reactivity of alkali metals increases down the group.

 Reactivity towards air:

Li forms monoxide, Na forms peroxide and other

metals form superoxides.

(i)4Li + O → 2Li O
2
2

(ii)2Na + O2 → Na O
2
2
(iii)M + O → MO (M = K, Rb, Cs)
2
2

 Li reacts directly with nitrogen of air to form Li N.
3

 Alkali metals are kept in kerosene oil because of
their high reactivity towards air and water.

Reactivity towards water: Forms metal hydroxide.

2M + 2H O → 2MOH +H (M = Alkali metal)
2
2;

Reactivity towards dihydrogen:

The alkali metals react with H at 673K except Li which
2
reacts at 1073K to form metal hydrides.

2M + H → 2MH
2