How do we account for the volatility of the hydrogen halide series?

Which is the same thing as saying that `HCl`, and `HBr`, and `HI`, have LOWER boiling points than that of `HF`.

AS a chemist, as a physical scientist, it is your responsibility to assess data not remember them, and we list the NORMAL boiling points as follows:

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WHY are the boiling points of `HF` and `H_2O` so disproportionately high? The answer is intermolecular hydrogen bonding. That is the electronegative fluorine atom polarizes electron density towards itself to give a resultant molecular dipole, i.e. a separation of charge: `""^(-delta)F-H^(delta+)`.

In the condensed phase, these dipoles line up to give a strong contributor to intermolecular force: `""^(-delta)F-H^(delta+)*F-H*F-H` etc.

And thus `HF` is the LEAST VOLATILE hydrogen halide.

Note that hydrogen bonding also occurs for `HCl`, and `HI`, and also `H_2S`, but because the dipole is of smaller magnitude, hydrogen-bonding does not make such a contribution to intermolecular force. The boiling points here follow the order of dispersion force, which increase with the number of electrons, and thus with the atomic number of the halogen/chalcogen.