Question

The liquefied hydrogen halides have the normal boiling points given above. The relatively high boiling point of HF can be correctly explained by which of the following?

a. HF gas is more ideal.
b. HF molecules have a smaller dipole moment.
c. HF is the strongest acid.
d. HF is much less soluble in water.
e. HF molecules tend to form hydrogen bonds.

Answer 1

The high boiling point of HF relative to other hydrogen halides is due to the presence of strong hydrogen bonds, which are a result of fluorine's high electronegativity and hydrogen's small size leading to unique physical properties.

Step-by-step explanation:

The relatively high boiling point of hydrogen fluoride (HF) compared to other hydrogen halides can be explained by the presence of hydrogen bonds in HF. The high electronegativity of fluorine compared to other halogens allows HF to exhibit very strong hydrogen bonding. This intermolecular force is significantly stronger than the London dispersion and dipole-dipole interactions that prevail in other hydrogen halides, resulting in the anomalously higher boiling point of HF. Furthermore, the small size of the hydrogen atom allows these dipoles to approach one another more closely, intensifying the hydrogen bonding effect.

Moreover, the trend in boiling points among the hydrides of group 15 to 17 shows that although the trends predict much lower boiling points based on molar mass alone, the actual boiling points are much higher due to the strength of hydrogen bonding. Hydrogen fluoride is a prime example of this, where its actual boiling point is far above the predicted value based on these trends, underscoring the impact of hydrogen bonding on physical properties like boiling points.