Chemical features of alkali metals:
(a) Reducing character: As the ionization enthalpies of the alkali metals decrease down the group their reducing character or reactivity in the gaseous state increases down the group. i.e., Li < Na < K < Rb < Cs.
(b) Reaction with dihydrogen: Alkali metals react with dry hydrogen at about 673 K to form crystalline hydrides which are ionic in nature and have high melting points.
(c) Oxides and hydroxides: Alkali metals when burnt in air form different compounds, for example the alkali metals on reaction with limited quantity of oxygen form normal oxides (M2O) M= Li, Na, K, Rb, Cs.
