Boiling point Pbr3 and PF3

(Polar molecules, Non-polar molecules, etc.)

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Boiling point Pbr3 and PF3

Postby lasarro » Mon Nov 18, 2019 9:34 pm

Why does PBr3 have a higher boiling point than PF3? I thought since the bonds in PF3 are stronger (smaller atoms--> shorter bond length --> stronger bond) it would have a much higher boiling point than PBr3. The solutions manual says that since PBr3 has more electrons, it has a higher boiling point. But I don't understand the correlation between the number of electrons and boiling point??

Brooke Yasuda 2J
Posts: 102
Joined: Sat Jul 20, 2019 12:17 am

Re: Boiling point Pbr3 and PF3

Postby Brooke Yasuda 2J » Mon Nov 18, 2019 9:43 pm

The number of electrons has to do with London Dispersion forces. The more electrons a molecule has, the more polarizable it is. And as we saw with the equation Potential Energy is proportional to - (polarizability of molecule 1) multiplied by (polarizability of molecule 2) divided by the distance to the sixth power, an increase in polarizability would increase attraction between the molecules resulting from dispersion forces. Therefore, PBr3 has a higher boiling point because both molecules will have dipole dipole and dispersion forces, but PBr3 has stronger dispersion force.

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