How are the volatilities of the Group 16, and Group 17 hydrides rationalized?
Two factors are important here: (i) hydrogen bonding; and (ii) dispersion forces.
Of course, water possesses the greatest degree of hydrogen bonding. Oxygen as a 1st row element, is far more electronegative than sulfur and tellurium, and the
For the other Group VI hydrides, dispersion forces are the dominant intermolecular force. Dispersion forces result from the transient polarization of the electron cloud. Thus bigger atoms, and bigger atoms in molecules, have a greater degree of dispersion forces, because there are more electrons, and more polarizable electron clouds. Thus after water,
That hydrogen sulfide has the lowest boiling point is harder to rationalize. The degree of hydrogen bonding for the
As an aside, you probably know that hydrogen sulfide smells pretty foul. It is also a fairly poisonous gas. When I was a grad student there was an inorganic lab next door that dealt with selenides and tellurides. Of course, a bit of sloppiness next door and the odour of hydrogen sulfide, hydrogen selenide, and hydrogen telluride would waft down the corridor, and sometimes cleared the floor, and sometimes the building. While