: 200
Valence (combining capacity) shows clear periodicity: Period 3 shows 1,2,3,4,3,2,1 pattern for Na through Cl (with respect to hydrogen). Maximum valence = group number for electropositive elements; = 8 - group number for electronegative elements.
Maximum oxidation state across Period 3: Na(+1), Mg(+2), Al(+3), Si(+4), P(+5), S(+6), Cl(+7). This equals the number of valence electrons.
Period 2 is limited: maximum OS = +4 (no d-orbitals for expansion). Period 3 and beyond can reach higher OS using d-orbitals: PCl5 (+5), SF6 (+6), IF7 (+7).
In d-block: maximum OS usually equals group number up to Mn(+7). Beyond Mn, maximum OS decreases because d-electrons become harder to remove (increasing Zeff). Fe max = +6 (not +8), Co max = +5, Ni max = +4.
The inert pair effect in heavier p-block elements stabilises lower OS: Tl(+1) > Tl(+3), Pb(+2) > Pb(+4), Bi(+3) > Bi(+5).