XX' $$ \to $$ Linear (e.g. ClF, BrF)

XX₃' $$ \to $$ T-Shape (e.g. ClF₃, BrF₃)

XX₅' $$ \to $$ Square pyramidal (e.g. BrF₅, IF₅)

XX₇' $$ \to $$ Pentagonal bipyramidal (e.g. IF₇)

The inertness of s-subshell electrons towards bond formation is known as inert pair effect. This effect increases down the group thus, for Sn, +4 oxidation state is more stable, whereas, for Pb, +2 oxidation state is more stable, i.e., Sn²⁺ is reducing while Pb⁴⁺ is oxidising

The acidic character of the oxoacids increases with increase in oxidation number of the halogen atom i.e.,

HClO < HClO₂ < HClO₃ < HClO₄

Since the stability of the anion decreases in the order.

ClO₄^- > ClO₃^- > ClO₂^- > ClO^–

Acid strength also decreases in the same order.

Bond dissociation enthalpy decreases as the bond distance increases from F2 to I2. This is due to increase in the size of the atom, on moving from F to I.

F – F bond dissociation enthalpy is smaller then Cl – Cl and even smaller than Br – Br. This is because F atom is very small and hence the three lone pairs of electrons on each F atom repel the bond pair holding the F-atoms in F₂ molecules.

The order of bond dissociation enthalpy is :

Cl₂ > Br₂ > F₂ > I₂