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

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

$AlCl_{3}+Cl^{-}\rightarrow AlCl_{4}^{-}$

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Initially, the aluminium is in the ground state and the valence orbital can be shown as:

Then the electron gets excited so, the valence orbital can be shown as:

So, initially, aluminium $(AlC_{3})$ was $sp^2$ hybridisation and hence having a trigonal planar shape.

Then it reacts with chloride ion to form $AlC_{4}^{-}$. Where it has the empty $3p_{z}$ orbital which gets involved and the hybridisation changes from $sp^2 \rightarrow sp^3$.

Hence there is a shape change from trigonal planar to tetrahedral.

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