Why does pf3 have greater bond angle than ph3 but nf3 has lesser bond angle than nh3?

Question

Answer

In PH3 , bonds are formed by pure orbitals and not hybrid orbitals i.e. px,py,pz orbitals bond with hydrogen atoms so bond angle is 90°, while in PF3, NH3 , & NF3 ,bonde are formed by hybrid orbitals

Answer

In nh3 nitrogen is more electronegative so it will attract electrons towards it, as a result repulsion occurs so bond angle is more. And in Nf3 fluorine is more electronegative so repulsion will be less and bond angle is also lesser than nh3. But in case of pf3 back bonding is possible so bond angle is more than ph3.

Answer

Introduction:
The bond angle in a molecule is determined by the repulsion between the electron pairs around the central atom. This repulsion is governed by the arrangement of these electron pairs, which can be influenced by factors such as electronegativity, the size of the atoms, and the number of lone pairs present. In the case of PF3 and PH3, the bond angle differs due to the electronegativity of the central atom. Similarly, in NF3 and NH3, the bond angle differs due to the presence of lone pairs on the central atom.

Bond Angle in PF3:
In PF3, the central atom is phosphorus, which is more electronegative than hydrogen. This means that the electron pairs in PF3 are more strongly attracted towards phosphorus compared to PH3. As a result, the electron pairs in PF3 are pushed closer to the central atom, leading to a smaller bond angle. The repulsion between the electron pairs is stronger, resulting in a larger bond angle. Therefore, PF3 has a greater bond angle compared to PH3.

Bond Angle in NF3:
In NF3, the central atom is nitrogen, which is more electronegative than hydrogen. Similar to PF3, the electron pairs in NF3 are more strongly attracted towards nitrogen compared to NH3. However, in this case, the bond angle is smaller in NF3 compared to NH3. The key factor here is the presence of a lone pair on the central atom in NF3. The lone pair occupies more space compared to a bonding pair, exerting greater repulsion on the bonding pairs. This repulsion pushes the bonding pairs closer together, resulting in a smaller bond angle. Therefore, NF3 has a smaller bond angle compared to NH3.

Summary:
- The bond angle in a molecule is influenced by factors such as electronegativity, atomic size, and the presence of lone pairs.
- PF3 has a greater bond angle than PH3 because the more electronegative central atom in PF3 attracts the electron pairs more strongly, pushing them closer together.
- NF3 has a smaller bond angle than NH3 due to the presence of a lone pair on the central atom. The lone pair exerts greater repulsion on the bonding pairs, resulting in a smaller bond angle.

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