What is inert pair effect?

In short,  the inert pair effect is a tendency of the electrons in the outermost atomic s orbital to remain unionized or unshared in compounds of post -transition metals .

Ans. Group 13 elements have ns2np1 electronic configuration. Hence they would be expected to be trivalent. In most of their compounds this is the case, however for the heavy elements lower oxidation states are more stable. Group 13 elements have ns²np¹ electronic configuration. Hence they would be expected to be trivalent. In most of their compounds this is the case, however for the heavy elements lower oxidation states are more stable. 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.

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.