Question

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

$AlC{l}_3+C{l}^{-}\to AlC{l}_4^{-}$

Answer 1

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 $s{p}^2$ hybridization to give a trigonal planar arrangement (in $AlC{l}_3$ ). To form $AlC{l}_4^{–}$ , the empty 3pz orbital also gets involved and the hybridization changes from $s{p}^2$ to $s{p}^3$ . As a result, the shape gets changed to tetrahedral.