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