When an alkali metal dissolves in liquid ammonia the solution can acquire different colours. Explain the reasons for this type of colour change.

Question

When an alkali metal dissolves in liquid ammonia the solution can acquire different colours . Explain the reasons for this type of colour change .

Philoid · Accepted Answer

When an alkali metal is dissolved in liquid ammonia, it results in the formation of a deep blue coloured solution.These solution of alkali metal in ammonia contains ammoniated cations and ammoniated electrons as shown below:
M + ( x + y ) NH₃→ M+(NH₃)x + e-(NH₃)y
The blue colour of the solution is imparted by ammoniated electrons which absorb energy corresponding to red region of the visible light for the their excitation to higher energy levels and transmit blue colour.