HCl, because the bond between the two atoms is ionic therefore highly polar. H donates an electron to rid itself of valence electrons and Cl accepts the electron to complete it's Argon-like valence. Each atom has an 'ideal' valence independent of each other so they can dissociate more easily.
He acts ideally because it is an ideal (noble) gas.
N2 and H2 achieve 'ideal' valence by sharing valence electrons. This type of bond is very strong. Nitrogen's covalent bond is so strong that it is nearly inert even at temperatures over 1000°F.