Final answer:
NH3 experiences hydrogen bonding due to the higher electronegativity of nitrogen, leading to a higher boiling point, while PH3 exhibits weaker dipole-dipole interactions without hydrogen bonding.
Step-by-step explanation:
The main intermolecular force in both NH3 (ammonia) and PH3 (phosphine) is hydrogen bonding and dipole-dipole interactions, respectively. Ammonia has a higher boiling point (-33 degrees Celsius) compared to phosphine (-88 degrees Celsius), which can be attributed to the hydrogen bonding present in NH3 due to the high electronegativity of nitrogen.
On the other hand, PH3 does not exhibit hydrogen bonding because phosphorus is less electronegative, leading to weaker dipole-dipole interactions. This is why NH3 has a boiling point that is significantly higher than what would be predicted based solely on its molecular weight, showing the profound effect of hydrogen bonding on physical properties.
In summary, NH3 exhibits hydrogen bonding in addition to dipole-dipole and dispersion forces, resulting in a higher boiling point. PH3, lacking hydrogen bonding, primarily exhibits weaker dipole-dipole and dispersion forces.