Bond angles of PF3 and PCl3

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.

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:-

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