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melting point of PCl5 vs PCl3

Why does pcl5 hv higher melting point than pcl3?

I understand that it is cuz it has greater mass/greater number of electrons, hence greater london force, but can't it not equally be argued that pcl5 is non polar because its trigonal bipyramidal and pcl3 is polar and so, theoretically PCl3 should have a higher melting point? 

Please advise.

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@Msj Chem The link doesn't work, it says you have reached a page that is unavailable for viewing.

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Posted (edited)

Let me try to help too :D I hope this will help you. 

PCl5 has a higher melting point than PCl3 is because of the larger intermolecular force between molecules in PCl5. PClexists as a covalent molecule in gaseous state, but usually it becomes charged in solid form as PCl4and PCl6. The structure of PCl5 is ionic lattice whilst PCl3 is in gaseous state in simple molecular structure. As we can see from the formula, PCl5 is a larger molecule with 5 P---Cl bonds than PCl3. The increase in dispersion force compensates the loss of polarity in PCl5, so larger number of protons and electrons will make the dispersion attraction greater. BUT,  it is understandable why you think PCl3 requires higher energy to break because of the permanent dipole because this is a special case.

If you want to learn more: https://goo.gl/Z6zq0C 

Edited by inriya
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