Why hydrogen chloride is a gas but hydrogen flouride is a liquid?

Answer 1

Hydrogen fluoride (HF) is a gas at room temperature, but does have a higher boiling point than hydrogen chloride (HCl).

Flourine is more electronegative than chlorine, so the HF molecule is more polar than the HCl molecule. This makes them more strongly attracted to one another (somewhat in the manner of magnets) and boiling a substance involves overcoming that intermolecular attraction.

Answer 2

Hydrogen chloride has weaker intermolecular forces, allowing it to exist as a gas at room temperature, while hydrogen fluoride has stronger intermolecular forces, making it a liquid under the same conditions. Specifically, hydrogen fluoride can form hydrogen bonds between molecules, leading to a higher boiling point compared to hydrogen chloride.