Which of the following statements best explains why the boiling point of NBr3 is higher than that of NH3?

• A. NBr3 forms hydrogen bonds, which increase its boiling point.
• B. Both NBr3 and NH3 have similar boiling points because they are both nitrogen compounds.
• C. NH3 has a higher boiling point because it is more polar than NBr3.
• D. NBr3 has stronger London dispersion forces due to its larger molecular size compared to NH3.

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the types of intermolecular forces present in NH3 and NBr3. NH3 (ammonia) is known to exhibit hydrogen bonding because it has N-H bonds, where hydrogen is directly bonded to a highly electronegative nitrogen atom.
2. Step 2: Recognize that NBr3 (nitrogen tribromide) does not have hydrogen atoms bonded to nitrogen, so it cannot form hydrogen bonds. Instead, its intermolecular forces are primarily London dispersion forces (induced dipole-induced dipole interactions).
3. Step 3: Compare the molecular sizes and molar masses of NH3 and NBr3. NBr3 has a much larger molar mass and a larger electron cloud due to the presence of bromine atoms, which increases the strength of London dispersion forces.
4. Step 4: Recall that boiling point is influenced by the strength of intermolecular forces. Stronger intermolecular forces require more energy (higher temperature) to overcome, leading to a higher boiling point.
5. Step 5: Conclude that although NH3 has hydrogen bonding, the much stronger London dispersion forces in the larger NBr3 molecule result in a higher boiling point for NBr3 compared to NH3.