Final answer:
In the AlCl3 molecule, Al has an sp2 hybridization, but when it bonds with an additional Cl- to form AlCl4-, it changes to sp3 hybridization to accommodate the extra bond. The change in hybridization of the Al atom in the reaction AlCl3 + Cl− → AlCl4− is from sp2 to sp3.
Step-by-step explanation:
The change in hybridization of the Al atom in the reaction AlCl3 + Cl− → AlCl4− is from sp2 to sp3. In AlCl3, the Al atom is bonded to three Cl atoms using three sigma bonds and has one unhybridized 2p orbital. When it reacts with Cl− to form AlCl4−, the Al atom forms a coordinate bond with a lone pair of electrons from Cl−, resulting in the hybridization of the empty 2p orbital with the 3s and two of the 3p orbitals, leading to sp3 hybridization.