Question

Why ammonia has a higher boiling point than phosphine.

Answer 1

Hint: Intermolecular forces of attraction are the attractive forces that exist between the molecules or ions. There are the four types of intermolecular forces which include electrostatic interactions, hydrogen bonding, dipole-dipole interactions and weak van der waal’s forces of attraction. The increasing order of these forces in terms of strength is given as: electrostatic interaction \[>\] hydrogen bonding \[>\] dipole-dipole \[>\] weak van der waal’s forces of attraction.

Complete answer:
The molecular formulas for ammonia and phosphine are \[N{{H}_{3}}\] and \[P{{H}_{3}}\], respectively. As we know, Nitrogen is more electronegative and smaller in size than phosphorus. Therefore, hydrogen bonding occurs in ammonia in comparison to phosphine. Hydrogen bonding is the force of attraction between hydrogen and an electronegative element which is smaller in size. In the case of phosphine, only weak van der waal’s forces of attraction exist between the molecules. Since hydrogen bonding is stronger than weak van der waal’s forces of attraction. Hence, ammonia has a higher boiling point than phosphine.
In all, we can say that hydrogen bonding is responsible for the higher boiling point of ammonia in comparison to phosphine.

Additional Information:
The electronegative elements which are involved in hydrogen bonding are fluorine, oxygen and nitrogen. Weak van der waal’s forces of attraction are also called London dispersion forces.

Note:
It is important to note that nitrogen is more electronegative and smaller in size than phosphorus. As a consequence,hydrogen bonding occurs in ammonia but not in phosphine. This hydrogen bonding between the ammonia molecules is responsible for the higher boiling point of ammonia in comparison to phosphine.