Question

boiling point of hydrogen chloride is lower than that of hydrogen fluoride why

Answer 1

Fluorine has the highest electronegativity of any atom. That means it likes to pull electrons toward it. When fluorine bonds with hydrogen, the polarity is so strong that it begins to exhibit the property of hydrogen bonding, which is in essence just an extreme dipole. Chlorine simply doesn’t have the pull of its halogen counterpart and can’t form that polar of a molecule.

In application, hydrogen fluoride will pull together due to hydrogen bonding, and more energy is required to separate the molecules to transition them from a liquid to a gas. The absence of the hydrogen bonding in hydrogen chloride means that it’s easier to pull the molecules apart.