f) Metallic character: The metallic character increases down the group.
g) Melting point and boiling point:: The m p and b p of alkali metals are very low and decrease with increase in atomic number.
h) Nature of bonds formed: These metals form ionic bonds. The ionic character increases as we down the group.
i) Flame colouration: All the alkali metals impart a characteristic colour to the flame.
j) Photoelectric effect: Alkali metals( except Li) exhibits photoelectric effect.
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.
Heat 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.
2 M + H2 2M + H-
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