Squae pyramidal Vs tripgonal bipyramid......Polarity
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There are two possible shapes for PCl5 i.e tripgonal bipyramidal and square pyramidal. The first one is non-polar overall despite the presence of polar P-Cl bonds.
But what about square pyramidal. The dipoles do not cancel out each other so it overall polar shape. Can you through some light on this issue.
Regards.
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Originally posted by Kahynickel:
There are two possible shapes for PCl5 i.e tripgonal bipyramidal and square pyramidal. The first one is non-polar overall despite the presence of polar P-Cl bonds.
But what about square pyramidal. The dipoles do not cancel out each other so it overall polar shape. Can you through some light on this issue.
If PCl5 were square pyramidal (which it is not), then yes it would be polar. But the square pyramidal molecular/ionic geometry is based on the octahedral electron geometry, which requires 6 electron charge clouds (eg. 5 bond pairs and 1 lone pair).In PCl5 (liquid and gaseous states), the P atom has 5 bond pairs and 0 lone pairs (since PCl5 is a neutral molecule with no net ionic charge which implies all atoms have no formal charges which accordingly implies that the P atom has 5 electrons from 5 bond pairs, as P is a Grp V element). Hence the PCl5 molecule has the trigonal bipyramidal (electron and molecular) geometry.
In the mechanism for forming the solid state PCl5 (from the liquid state), a Cl- ion is eliminated from one PCl5 molecule, to nucleophilically add onto the electrophilic P atom of a neighbouring PCl5 molecule, generating the PCl4+ cation (with tetrahedral ionic geometry) and the PCl6- anion (with octahedral ionic geometry).
Therefore in accordance to their geometries, all 3 species, ie. the trigonal bipyramidal PCl5 molecule, the tetrahedral PCl4+ cation, and the octahedral PCl6- anion, are all non-polar species.
image credits : http://en.wikipedia.org/wiki/Phosphorus_pentachloride