p-Block Elements
p-Block Elements tests periodic trends, anomalous behaviour, oxides and oxoacids, halogens, interhalogens and noble-gas compounds. Group comparisons are more important than isolated facts.
Group trends
Down group 15, metallic character increases and the acidic character of oxides decreases: N2O5 and P4O10 are acidic, Sb2O3 is amphoteric, Bi2O3 is basic. N2 is inert because of its triple bond. Down group 17, oxidising power falls F2 > Cl2 > Br2 > I2; F2 is the strongest oxidiser and never shows positive oxidation states. Chlorine disproportionates in alkali: cold dilute gives Cl- and ClO-; hot concentrated gives Cl- and ClO3-.
Noble gases and interhalogens
Xe forms XeF2 (linear), XeF4 (square planar) and XeF6 (distorted octahedral). Interhalogens include ClF3 (T-shaped), BrF5 (square pyramidal) and IF7 (pentagonal bipyramidal). Their reactivity increases with the size difference between the halogens.
Worked example
Chlorine with cold dilute NaOH: Cl2 + 2NaOH -> NaCl + NaOCl + H2O. Chlorine goes from 0 to -1 in NaCl and 0 to +1 in NaOCl. One element is simultaneously oxidised and reduced, so this is disproportionation. With hot concentrated NaOH the products are NaCl and NaClO3, where chlorine reaches +5.
Traps
Writing F2 as a positive oxidation state, calling SO2 bleaching oxidative (it is reductive), and confusing the cold and hot alkali products are common errors.