Question

Why is hydrogen fluoride a liquid unlike other hydrogen halides?

Answer 1

Hydrogen bonding:

• Hydrogen bonding is an electrostatic attraction between a hydrogen atom covalently bonded to a highly electronegative atom and another electronegative atom in the vicinity.
• Example: Water and chloroform.
• Two types of hydrogen bonding exist intermolecular hydrogen bonding and intramolecular hydrogen bonding.

Hydrogen fluoride is a liquid:

• Due to the high electronegativity of the fluorine atom, there is strong intermolecular hydrogen bonding between hydrogen and the fluorine atom in hydrogen fluoride $\left(\mathrm{HF}\right)$.
• $\mathrm{HF}$ is in a liquid state at room temperature due to this intermolecular hydrogen bonding.
• Except for $\mathrm{HF}$, all other hydrogen halides are gaseous at room temperature.
• $\mathrm{Cl}$, $\mathrm{Br}$, and $\mathrm{I}$ have less electronegativity than fluorine.
• As a result, the interaction forces between hydrogen chloride $\left(\mathrm{HCl}\right)$, hydrogen bromide $\left(\mathrm{HBr}\right)$, and hydrogen iodide $\left(\mathrm{HI}\right)$ will be weak.