Explain how chlorine exhibits a maximum covalency of 7.

Explanation

Electronic configuration of Cl is `[Ne] 3s^(2) 3p^(5)`. In third shell, there are vacant d orbitals.
The paired electrons of 3s and 3p orbitals can be excited to 3d orbitals. Therefore, the number of unpaired electrons increases. As a result, covalency corresponding to the number of unparied electrons is exhibited. In the fully excited state of Cl atom, there are seven half-filled orbitals giving covalency of 7. As there is no scope for further excitation, it is the maximum covalency that chlorine can show.