the temperature for the following to reach a pressure of 100mmHg is as follows(celcius)) HI -> -72.1 HCl -> -114 HBr -> -97.7 HF -> -28.2 how can this be? since they are all combinations of H and an element of the last column before the noble gas surely the smaller the size of the molecule, the higher the temperature will be? since they are all a combination of H and an atom whose radius goes R=(F<Cl<Br<I) so the electronegativity goes (F>Cl>Br>I). surely the temp should go with the electronegativity??