Ncert Exercises & Solutions

4.25 Describe the change in hybridisation (if any) of the Al atom in the following reaction.

$A l C l_{3} + C l^{-} \to A l C l_{4}^{-}$

The valence orbital picture of aluminium in the ground state can be represented as:

The orbital picture of aluminium in the excited state can be represented as:

Hence, it undergoes sp $^{2}$ hybridization to give a trigonal planar arrangement (in AlCl $_{3}$ ). To

form ${AlCl}^{4 -}$

, the empty 3p $_{z}$ orbital also gets involved and the hybridization changes from sp $^{2}$

to sp $^{3}$ . As a result, the shape gets changed to tetrahedral.