Question

Using the VSEPR theory, what would you predict the shape of the PCI3 molecule to be?

Answer 1

`"Trigonal pyramidal..............."`

Explanation:

There are 4 regions of electron density around the central phosphorus atom: `3xxP-Cl` bonds, and one phosphorus-centred lone pair. These adopt a tetrahedral geometry as the shape which minimizes electron-pair interactions. But because we describe molecular geometry on the basis of bonding pairs of electrons, symmetry descends to trigonal pyramidal.

Because `ddotP` has a lone pair, which is close to the phosphorus atom, `/_Cl-P-Cl` should be somewhat compressed from `109.5^@`.