Question

Which is more stable \[PbC{{l}_{2}}\] or \[PbC{{l}_{4}}.\]

Answer 1

Hint: We know that the stability of compounds containing similar chemical species we can look at whether the reaction is endothermic or exothermic. Another way to check stability is to check whether the compound exists.

Complete answer:
But in heavier members, we usually notice that the tendency to show two oxidation states increases in the sequence. Now, here a common doubt arises what reasons influence this change in behaviour of the carbon family So, we will try to understand this by a condition known as inert pair effect. First, we will try to understand two terms related to inert pair effect: Effective nuclear charge: It is generally defined as the net positive charge experienced by an atom inside its nucleus. Shielding effect: Outer electrons experience a nuclear attraction from the positive charges of the nucleus and face repulsion from the similarly charged inner electrons. So, due to immense repulsion by the inner shell electrons, the valence electrons experience reduction in attraction from the nucleus, and thus the reduced attraction between the nucleus and electrons is referred to as shielding effect.
The inert pair effect is the tendency of the two electrons in the outermost atomic s orbital to remain unionized or unshared in compounds of post-transition metals., out of which \[\left( Pb \right)\] lead is one. The term inert pair effect is often used in relation to the increasing stability of oxidation states, that are two less than the group valency for the heavier elements of groups \[13,\text{ }14,\text{ }15\] and \[16.\]The s electrons are more tightly bound to the nucleus and therefore more difficult to ionize. Due to the inert pair effect, the higher oxidation state of an element is not stable as we move down the groups. Thus, in other words, \[P{{b}^{+4}}~\] is less stable than \[P{{b}^{+2}},\] hence \[PbC{{l}_{4}}\] ​ is also less stable.

Note:
Remember that the poor shielding effect of d block and f block it means due to poor contraction of d block electrons in the s orbital are more strongly held in the upper period of the same group. So, s electrons are inert and cannot be removed and give a valency.