Acidic nature: H2O < H2S < H2Se < H2Te
This is because the H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
Thermal stability: H2O < H2S < H2Se < H2Te < H2Po
This is because the H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
Reducing character: H2O < H2S < H2Se < H2Te < H2P
This is because the H-E bond length increases down the group. Therefore, the bond dissociation enthalpy decreases down the group.
30. Reactivity with oxygen: EO2 and EO3
Reducing character of dioxides decreases down the group because oxygen has a strong positive field which attracts the hydroxyl group and removal of H + becomes easy.
Acidity also decreases down the group.
SO2 is a gas whereas SeO2 is solid. This is because SeO2 has a chain polymeric structure whereas SO2 forms discrete units.