[CKabes]

The boiling points of the halogens bonded to hydrogen are as follows in degrees C (approx):

HF: 19.5
HCl: -85
HBr: -66.8
HI: -35

Why is it that HCl has the lowest boiling point and not HI? Doesn't HI have the smallest dipole moment, giving it the weakest inter-molecular bonds?

[Stovn0611]

My guess would be because HI has stronger London dispersion forces, resulting in stronger inter-molecular bonds that compensate for the weaker inter-molecular bonds from the small dipole moment

[formaldehyde23]

Yes, Stovn0611 is correct. HF has the highest boiling point because it is the hydrogen halide that has hydrogen bonds. HI has the second highest boiling point because it has the second highest intermolecular forces, or the greatest london dispersion force. This is because Iodine is the largest atom.