Question -
Answer -
The valence orbitalpicture of aluminium in the ground state can be represented as:
The orbital picture ofaluminium in the excited state can be represented as:
Hence, it undergoes sp2 hybridization togive a trigonal planar arrangement (in AlCl3).
Toform AlCl4–, the empty 3pz orbital also getsinvolved and the hybridization changes from sp2 to sp3. As a result, the shapegets changed to tetrahedral.