Predicting Characteristic Oxidation State from Periodic Position

Predicting an element's characteristic oxidation state means reading its group number for the maximum expected value, then checking how far down the p-block group the element sits: the inert pair effect grows down the group, so the lowered state (two below the maximum) appears alongside the group state in heavier-but-not-heaviest members, and dominates outright in the heaviest member.

For thallium, group 13 predicts a maximum of 3+, but thallium is the heaviest group 13 member, so the inert pair effect (Chem 2299) predicts its dominant oxidation state is 1+, matching its observed chemistry. For tin, group 14 predicts 4+; tin is heavier but not the heaviest member of its group, so the inert pair effect predicts Sn2+ appears alongside Sn4+ rather than dominating, matching tin's mixed 2+/4+ chemistry. For silicon, group 14 predicts 4+, and silicon sits near the light end of its group, so no inert pair adjustment applies and 4+ is the correctly predicted stable state.