`NH_3` has exceptionally high melting point and boiling point as compared to those of the hydrides of the remaining element of group 15. Explain.

Explanation

(i) `NH_(3)` has exceptionally high melting point and boiling point due to hydrogen bonding between `NH_(3)` molecules.
(ii) Each molecule can form a maximum of 4 hydrogen bonds but on average 1 hydrogen bond per molecule as there is only one lone pair on `NH_(3)` available for hydrogen bonding.
(iii) Hydrogen bonding is strong intermolecular attraction as H on `NH_(3)` acts like a proton due to partial positive on it whole N has the partial negative charge. Thus when the very polarized H comes close to a N atom in another `NH_(3)` molecule, a very strong hydrogen bond is formed.
(iv) Due to much strong intermolecular interactions compared to weaker permanent dipole-dipole interactions between other`XH_(3)` , molecules in group 15, large amount of melting point.