Why is the boiling point of NH_3 higher than the boiling point of PH_3 and AsH_3?

1 Answer
anor277
Sep 25, 2016

Because the degree and magnitude of intermolecular bonding between ammonia molecules is much greater than that between phosphine, and arsine molecules.

Explanation:

Ammonia, boiling point -33 ""^@C, has demonstrably greater intermolecular bonding than that of phosphine, boiling point -87.7 ""^@C, or that of arsine, boiling point -62.5 ""^@C. The difference in intermolecular bonding may be attributed to the degree of hydrogen bonding in each solvent. In ammonia, hydrogen is bound to a strongly electronegative element in nitrogen, and the resultant hydrogen bonding between molecules constitutes a potent intermolecular force.

On the other hand, phosphorus and arsenic are much less electronegative compared to nitrogen, and hydrogen bonding does not operate in their hydrides as an intermolecular force.

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