Question

Why is the boiling point of $N{{H}_{3}}$ higher than the boiling point of $P{{H}_{3}}$ and $As{{H}_{3}}$ ?

Answer 1

A substance's boiling point is the temperature at which the vapour pressure of a liquid equals the pressure around the liquid and the liquid transforms into a vapour. The boiling point of a liquid is affected by the surrounding atmospheric pressure. The boiling point of a liquid in a partial vacuum is lower than the boiling point of the same liquid at atmospheric pressure. The boiling point of a liquid at high pressure is greater than the boiling point of the same liquid at atmospheric pressure.

Complete answer:
Intermolecular and intramolecular hydrogen bonding are the two kinds of hydrogen bonding that have been identified. Intramolecular forces exist between two atoms in a molecule, whereas intermolecular forces exist inside the same molecule. Intermolecular aggregation forces rise as a result of hydrogen bonding, which is reflected in the boiling point and solubility of the organic molecule. This is a type of dipole-dipole interaction that only happens when a hydrogen atom is linked to either oxygen, nitrogen, or fluorine. The formation of an intermolecular hydrogen bond causes molecules to bind together.
Ammonia, with a boiling temperature of $-33{}^\circ C$ , has significantly more intermolecular bonding than phosphine, with a boiling point of $-87.7{}^\circ C$ , or arsine, with a boiling point of $-62.5{}^\circ C$ . The degree of hydrogen bonding in each solvent may explain the differences in intermolecular bonding. Hydrogen is linked to a strongly electronegative element in nitrogen in ammonia, and the hydrogen bonding between molecules results in a strong intermolecular force.
Phosphorus and arsenic, on the other hand, are significantly less electronegative than nitrogen, and hydrogen bonding does not act as an intermolecular force in their hydrides.
Because the degree and magnitude of intermolecular interaction between ammonia molecules is significantly larger than the degree and magnitude of intermolecular bonding between phosphine and arsine molecules.

Note:
The Nitrogen family, which comprises nitrogen, phosphorus, arsenic, antimony, and bismuth elements, is also known as Group 15. The Representative Elements, which are located on the right side of the main periodic table, are also known as the p-block elements. The electrical arrangement of the valence shell has a significant impact on how an element behaves. Group 15 elements have the valence electron shell structure $n{{s}^{2}}n{{p}^{6}}$ .