Question

Why inert pair effect strongly exist in heavy p block elements?

Answer 1

As we move down the group, the intervening d and f electrons shield the ns2 electrons poorly and hence the ns2 electrons are pushed inside towards the nucleus This results in the reluctance of ns electrons to participate in bond formation and this phenomenon is called Inert pair effect.

.1s electrons of these elements have high momenta which leads to increased mass decreased orbital size. Thus these behave more like core electrons than valence electrons.

So, while lighter p-block elements (like Al) usually "give away" their s and p electrons when they form chemical compounds, heavier p-block elements (like Tl) tend to "give away" their p electrons but keep their s electrons. That's the reason why for example Al(III) is preferred over Al(I) but Tl(I)is preferred over Tl(III).

Source:chemistry stack exchange

Hope it helps

Happy reading