Question

Compounds that experience hydrogen bonding between molecules generally have higher boiling points. Because of hydrogen bonding, the intermolecular forces of attraction between molecules within the compound are high. Consequently, more energy is required to separate these molecules from one another through boiling. Watch the animation in the introduction to examine the effect of hydrogen bonding on the boiling points of hydrides belonging to groups 4A and 6A. The hydrides of group 5A are NH₃, PH₃, AsH₃, and SbH₃. Arrange them from highest to lowest boiling point.

A) NH₃ > PH₃ > AsH₃ > SbH₃
B) SbH₃ > AsH₃ > PH₃ > NH₃
C) PH₃ > NH₃ > SbH₃ > AsH₃
D) AsH₃ > SbH₃ > NH₃ > PH₃

Answer 1

The hydrides of group 5A should be arranged in order of decreasing boiling points as NH₃ (ammonia) having the highest due to strong hydrogen bonding, followed by PH₃ (phosphine), AsH₃ (arsine), and SbH₃ (stibine) with the lowest.

Step-by-step explanation:

Hydrogen bonds significantly influence the boiling points of compounds. In the case of the hydrides of group 5A, such as NH₃, PH₃, AsH₃, and SbH₃, the intermolecular forces need to be considered to determine their boiling points. Among these, NH₃ exhibits hydrogen bonding due to the presence of a highly electronegative nitrogen atom, resulting in a much higher boiling point compared to the others in the series. As we move from NH₃ to PH₃, AsH₃, and then to SbH₃, the size of the molecules increases but the strength of hydrogen bonding decreases, as phosphorus, arsenic, and antimony are less electronegative than nitrogen.

Therefore, the correct order from highest to lowest boiling point is: NH₃ > PH₃ > AsH₃ > SbH₃, corresponding to option A) NH₃ > PH₃ > AsH₃ > SbH₃.