In what respects `H_(2)` differs from alkali metals and halogens ?

Explanation

Difference with alkali metals.
1. Hydrogen is a non-metal whereas alkali metals are electropositive elements.
2. Hydrogen from diatomic molecules whereas alkali metals do not.
3. Hydrogen mostly froms covalent compounds whereas alkali metals mostly from ionic compounds.
4. The ionization energy of hydrogen is much higher than that of a alkali metals.
The size of H is smaller than those of alkali metals.
Difference with halogens
1. It has less tendency to form hydrides (H^(-))` as compare to halogens.
2. It does not have lone pair of electrons like halgens.
3. It is less reactiv than halogens due to high bond dissociation energy.