Question

which statement best helps to explain the observation that nh₃(l) boils at -28°c, whereas ph₃(l) boils at -126°c?
a the dispersion forces in nh₃ are weaker than the dispersion forces in ph₃.
b the dispersion forces in nh₃ are stronger than the dipole - dipole forces in ph₃.
c nh₃ has hydrogen bonding that is stronger than the dipole - dipole forces in ph₃
d nh₃ has hydrogen bonding that is weaker than the dipole - dipole forces in ph₃.

Explanation:

• Boiling point is related to the strength of intermolecular forces.
• \(NH_3\) has hydrogen bonding (a special type of strong dipole - dipole force due to the highly electronegative \(N\) atom and \(H\) atom attached to it).
• \(PH_3\) has only dipole - dipole forces (since \(P\) is less electronegative than \(N\) and does not form hydrogen bonds).
• Stronger intermolecular forces lead to a higher boiling point. Since \(NH_3\) has a higher boiling point (\(- 28^{\circ}C\)) than \(PH_3\) (\(-126^{\circ}C\)), the hydrogen bonding in \(NH_3\) is stronger than the dipole - dipole forces in \(PH_3\).

Answer:

C. \(NH_3\) has hydrogen bonding that is stronger than the dipole - dipole forces in \(PH_3\)