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PH3 and PF3 are pyramidal in shap with one lone pair on P. But PF3 has greater bond angle than PH3... why...???

PH3 and PF3 are pyramidal in shap with one lone pair on P. But PF3 has greater bond angle than PH3... why...???

Grade:12

1 Answers

Aman Bansal
592 Points
12 years ago

Dear Abhijat,

Both NH3 and NF3 are pyramidal in shape with one lone pair on N. However F has higher electronegativity than H, the electron pair is attracted more towards F in NF3 i.e. the bond pairs of electrons are away from N or in other words distance between bond pairs ion is more. Hence repulsion between bond pairs in NF3 is less than NH3. Hence the lone pair repels the bond pairs of NF3 more than it does in NH3. As a result, the bond angle decreases to 102.4°. Whereas in NH3 it decreases to 107.3° only.
PH3 and PF3 are also pyramidal in shape with one lone pair on P. But PF3 has greater bond angle than PH3 (opposite to NH­3 and NF3). This is due to resonance in PF3, leading to partial double bond character as shown below
As result repulsions between P – F bonds are large and hence the bond angle is large. There is no possibility of formation of double bonds in PH3.
l.

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