question_answer

Boiling point of phosphine is lesser than that of ammonia though its molecular size is more. Assign reason. Therefore, boiling point of ammonia is more than that of phosphine.

Answer:

                In ammonia \[(N{{H}_{3}}),\] the molecules are involved in the intermolecular hydrogen bonding on account of the polarity of N-H bonds. But the same is not possible in molecules of phosphine \[(P{{H}_{3}})\] since the polarity of P-H bond is negligible as compared to N-H bond. This is due to lesser electro negativity of phosphorus (2.1) as compared to nitrogen (3.0). Therefore, boiling point of ammonia is more than that of phosphine.