According to VSEPR theory, what is the shape of the PH3 molecule best described as?

1 Answer
anor277 · Aditya Banerjee.
Oct 8, 2016

The shape of phosphine is pyramidal; i.e. it is an analogue of ammonia.

Explanation:

There are 5+3 valence electrons for which to account; and this gives 4 electron pairs arranged the central phosphorus atom. These assume a tetrahedral geometry, however, one of the arms of the tetrahedron is a lone pair, and geometry descends to trigonal pyramidal with respect to phosphorus.

The ∠H−P−H ≅ 94∘, whereas that for ∠H−N−H≅105∘. This difference in bond angles between the homologues is not readily rationalized, and beyond the scope of even a third year inorganic chemist. This bond angle discrepancy is also observed for H2S versus H2O.

So, the shape is PYRAMIDAL :
![webelements.com](useruploads.socratic.org)

Hope it Helps :)

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