Which of the following substances is expected to have the highest boiling point?
Show the answer and explanation
Correct answer
B. HF
Principle or equation
Boiling point depends on the strength of intermolecular forces. Hydrogen bonding is stronger than dipole-dipole interactions and London dispersion forces. HF can form hydrogen bonds, while HCl, HBr, and CH4 cannot.
Why this answer is correct
HF has hydrogen bonding due to the highly electronegative fluorine atom bonded to hydrogen. CH4 is nonpolar and only has weak London dispersion forces. HCl and HBr are polar but do not form hydrogen bonds; their dipole-dipole forces are weaker than hydrogen bonds. Thus HF has the highest boiling point.
Example
Water (H2O) has a higher boiling point than H2S because of hydrogen bonding.
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