1. Hydrogen Bonding:
* Ammonia can form hydrogen bonds due to the high electronegativity of nitrogen and the presence of lone pairs of electrons.
* Hydrogen bonds are strong intermolecular forces that require a significant amount of energy to break, leading to a higher boiling point.
* Phosphine, on the other hand, cannot form hydrogen bonds because phosphorus is less electronegative than nitrogen and the P-H bond is less polar.
2. Molecular Shape:
* Ammonia has a pyramidal shape with a lone pair of electrons on the nitrogen atom. This lone pair contributes to the polarity of the molecule and strengthens hydrogen bonding.
* Phosphine has a trigonal pyramidal shape but is less polar than ammonia due to the larger size of the phosphorus atom.
3. Molecular Weight:
* While molecular weight plays a role in boiling point, it is less significant in this case. Ammonia and phosphine have similar molecular weights.
In summary:
The ability of ammonia to form strong hydrogen bonds due to its polar nature and lone pair of electrons is the primary reason for its higher boiling point compared to phosphine.
