In case of PF3 the size of F is small and thus it approaches near to the central atom that is P.

as it approaches near to P there comes the repulsion between the bond pairs,

which widens the bond angle and makes it larger than in case of PCl3.

Here two types of forces are deployed

  1. Bond pair – lone pair repulsions
  2. Bond pair –bond pair repulsions.

In case of the PF3 , the bond pair- bond pair repulsions compensate the effect of lone pair-bond pair repulsions. Thus the bond angle is larger as it has to face lesser repulsion in case of P-F-P bond angle.

Structure of PF3

In case of PCl3 , the size of Cl is larger as compared to F. so in this case the bonds are longer and bond pairs have enough space between them. and the lone pair – bond pair repulsion plays a bigger role in deciding the bond angle . So the bond angle is decreased due to the compression of bonds by repulsion of lone pair. As shown below:-

Structure of PCl3

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