`SOCl_(2)` can act as a weak acid as well as a weak base. Explain.

Explanation

(a) N does not have d-orbitals to accommodate the electrons donated by O of `H_(2)O`, therefore, attack of `H_(2)O` occurs on the Cl atom which has d-orbitals to accommodate the extra electrons donated by `H_(2)O`. Consequently Cl-O bond is fomed leading to the formation of HOCl and `NH_(3)` as shown below :

In contrast, both P and Cl have d-orbitals to accommodate electrons donated by `H_(2)O`. But P-O bond is much stronger than Cl-O bond. As a result, attack of `H_(2)O` molecules occurs preferentially on P of `PCl_(3)` to form `H_(3)PO_(3)` and HCl.

(b) The basic character of `SOCl_(2)` is due to the presence of a lone pair of electrons on the S-atom. Futher, in `SOCl_(2)`, S also has empty d-orbitals which can be used to accept electrons. Therefore, `SOCl_(2)` also behaves as a Lewis acid.