: 200
Thermal stability of hydrides decreases down each group: NH3 > PH3 > AsH3 (E-H bond weakens as size increases). Consequently, reducing character increases inversely.
Acid strength across a period: NH3 < H2O < HF (increasing EN). Down a group: HF < HCl < HBr < HI (decreasing bond strength dominates over EN).
Boiling points show H-bonding anomalies: NH3, H2O, HF have anomalously high b.p. due to hydrogen bonding. For non-H-bonding hydrides, b.p. increases with molecular mass (van der Waals forces): H2S < H2Se < H2Te; PH3 < AsH3 < SbH3.
HF is the only hydrogen halide that is a weak acid (Ka = 6.6 x 10^-4). Bond energy H-F = 568 kJ/mol is simply too high for easy dissociation.
Catenation in hydrides: maximum for carbon (alkanes, alkenes, alkynes) followed distantly by silicon (silanes up to Si6H14). N, O, S show limited catenation (N2H4, H2O2, H2S2).
Bond angles decrease down each group: NH3(107) > PH3(93) > AsH3(92). Larger central atoms use more pure p-orbitals, approaching 90 degrees.