When the alkali metal is dissolved in liquid ammonia, a deep blue coloured solution is formed.
M +(x +y)NH3= [M(NH3 )x ]+ + [e (NH3 )y ]-
The ammoniated electrons absorb energy corresponding to red region of visible light. Therefore, the transmitted light is deep blue in colour.
Clusters of metal ions are formed at higher concentration (3M) which causes the solution to attain a copper-bronze colour and a metallic lustre.
