Chemistry- electronegativity and bonding

[Dell]

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??

 

[chemisttree]

It might be a combination of electronegativity, mass, hydrogen bonding, size, etc...

 

[Blueshift5]

The temperature needed for a substance to reach a certain pressure is dependent on a variety of factors, including the size and shape of the molecules, the strength of intermolecular forces, and the strength of the bonds between atoms. While electronegativity does play a role in determining the strength of bonds, it is not the only factor at play.

In the case of these compounds, the difference in electronegativity between hydrogen and the other element is not the only factor that affects the boiling point. For example, HI has a smaller difference in electronegativity compared to HBr, but it has a higher boiling point. This is because HI molecules are larger and have stronger intermolecular forces, making it more difficult for them to escape into the gas phase.

Additionally, the presence of lone pairs on the halogen atoms in these compounds also affects their boiling points. Lone pairs can contribute to stronger intermolecular forces, making it more difficult for the molecules to escape into the gas phase.

Overall, while electronegativity does play a role in determining the boiling point of a compound, it is not the only factor at play. Other factors such as molecular size, shape, and intermolecular forces also play a significant role in determining the temperature needed for a substance to reach a certain pressure.