Inert Pair Effect [ENDORSED]

[Krupa Prajapati]

Could someone please explain the inert pair effect and how exactly that relates to the concept of variable valence? Thank you!

[Chem_Mod]

The inert pair effect describes the tendency for Group 13-15 elements to take on two different oxidation state charges, differing by two charge units. For example, Sn forms 2+ and 4+, which is similar to SB which forms 3+ and 5+ cations, which is similar to Bi, which forms 3+ and 5+ cations, etc.

This is explained due to the fact that after Group 13, the valence s electrons are relatively low energy due to the weakened shielding effects of the d orbitals. Thus, the valence s electrons often stay attached to the atoms during ion formation depending on the circumstances. This is the source of the name "inert pair." The "pair" that is being referred to is the s electron pair. It is said to be "inert" (or at least somewhat "lazy," using the language of Atkins :) ) because they tend to stay attached to the atom during ion formation for elements in Groups 13-15.