Inert Pair Effect

Question

Why does lead show a more stable +2 oxidation state than +4 while carbon at the top of the same group prefers a +4 state?

RankGuru · Accepted Answer

The inert pair effect is the reluctance of the outermost ns^2 pair of electrons to participate in bonding among the heavier elements of Groups 13 to 16. As one moves down a group, the ns electrons become increasingly held in place because of poor shielding by intervening d and f electrons, which causes weak penetration and reduced bonding tendency of the s pair. In lead, the 6s^2 pair tends to remain inert, so the +2 oxidation state, which uses only the two p electrons, becomes more stable than the +4 state that would also require the s pair. Carbon, lacking these inner d and f electrons, readily uses all four valence electrons and prefers the +4 state. The option that lead is more electronegative is false. The option that carbon is a metal is incorrect, since carbon is a non-metal. The option of fewer valence electrons is wrong, as both have four. This effect is a key JEE Advanced periodicity concept. Plausibility check: the stability order Sn^4+ > Pb^2+ and the oxidising nature of PbO_2 confirm the inert pair stabilisation of lead's lower state.

Inert Pair Effect

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