- Why do the stability of +6 oxidation state decreases down the group and stability of +4 oxidation state increases down the group in group 16 elements?
This is due to inert pair effect. Inert pair effect may be defined as inertness of inner ns sub-shell towards chemical reaction. Group 16 elements have ns2np4 electronic configuration. Hence they would be expected to be have maximum oxidation state +6. But the heavy elements show lower oxidation states i.e., +4. This is explained by the s electrons remaining paired and not participating in bond formation. This inertness of s-subshell electrons towards the bond formation is called inert pair effect. This happens because the s orbitals are held closer to the nucleus, therefore the electrons present in s orbitals are held strongly by nucleus because of large electrostatic forces. Hence the energy required to unpair the s-electrons is high because of which they remain paired. So, +6 oxidation state will be exhibited by the ligjhter elements or we can say that stability of +6 oxidation state decreases and +4 oxidation state increases down the group.