PCl3 and PCl5 melting point difference

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phenomenon.ahmad
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Well... as we all know PCl3 is a polar molecule cause of its dipole while PCl5 is non polar because it has no net dipole moment. So technically PCl3 should have higher melting point cause of permanent dipole but in reality PCl3 is a colorless liquid at r.t while PCl5 is a white solid. Why?

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shengoc
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(Original post by phenomenon.ahmad)
Well... as we all know PCl3 is a polar molecule cause of its dipole while PCl5 is non polar because it has no net dipole moment. So technically PCl3 should have higher melting point cause of permanent dipole but in reality PCl3 is a colorless liquid at r.t while PCl5 is a white solid. Why?

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ermm, permanent dipole is just one type of intermolecular forces, isnt it?

for simple covalent molecules, mp and bp is dependent on combinations of ALL intermolecular forces, isn't it?

if so, what other intermolecular forces could be present that could help explain this phenomenon ?(i mean in chemistry, you can only predict, but hey given an observation, you use what you know then to explain that phenomenon)
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phenomenon.ahmad
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(Original post by shengoc)
ermm, permanent dipole is just one type of intermolecular forces, isnt it?

for simple covalent molecules, mp and bp is dependent on combinations of ALL intermolecular forces, isn't it?

if so, what other intermolecular forces could be present that could help explain this phenomenon ?(i mean in chemistry, you can only predict, but hey given an observation, you use what you know then to explain that phenomenon)
Sorry for the noobiness but at a levels, i've only been taught about permanent dipole force that is relevant to the given scenario. So what other forces are responsible?

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shengoc
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(Original post by phenomenon.ahmad)
Sorry for the noobiness but at a levels, i've only been taught about permanent dipole force that is relevant to the given scenario. So what other forces are responsible?

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this, http://www.chemguide.co.uk/atoms/bonding/vdw.html
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phenomenon.ahmad
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Ok thanks for your help

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Surodeep
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PCl5 ,in the solid form, exists as a salt in the form [PCl4] [PCl6]-rather than being in the trigonal bipyramidal form.This makes it a crystalline white solid. As far as boiling point is concerned, PCl3 does have a lower boining point than PCl5 because of the greater polarity as PCl3 has a trigonal pyramidal structure with a net dipole moment while PCl5 is non polar.
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