Chemistry / Unit 12 Chem 2341 worked example, 60 to 90 seconds
Predicting Characteristic Oxidation State from Periodic Position
The idea
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.
In practice
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.
Where people slip
Expecting the lowered state to dominate for a heavier-but-not-heaviest member like tin or indium, the way it does for thallium, lead, or bismuth, overstates how far down the group the effect has fully taken hold.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Something wrong in this lesson? Flag it · Sources for Chemistry