Vsepr & Hybridisation
Which statement best explains why PF5 is stable while NF5 is not?
Select the correct option:
Solution
Phosphorus can expand octet using available d orbitals effectively; nitrogen cannot due to absence of low-energy d orbitals
- Valence Shells:
- Nitrogen is in the 2nd period: Electron configuration [He]2s22p3. It has no d orbitals in its valence shell.
- Phosphorus is in the 3rd period: Electron configuration [Ne]3s23p3. It has vacant, low-energy 3d orbitals.
- Octet Expansion: To form 5 covalent bonds, an atom must accommodate 10 electrons in its valence shell (expanded octet).
- Outcome: Phosphorus can promote an electron to the 3d orbital and form sp3d bonds. Nitrogen is strictly limited by the 'Octet Rule' and cannot form 5 bonds.
- Sterics: Additionally, Nitrogen is so small that having 5 large atoms around it would cause extreme steric repulsion.
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About This Question
- Subject
- chemistry
- Chapter
- chemical bonding and molecular structure
- Topic
- vsepr & hybridisation
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Phosphorus can expand octet using available d orbitals effectively; nitrogen cannot due to absence of low-energy d orbitals
- Valence Shells:
- Nitrogen is in the 2nd period: Electron configuration [He]2s22p3. It has no d orbitals in its valence shell.
- Phosphorus is in the 3rd period: Electron configuration [Ne]3s23p3. It has vacant, low-energy 3d orbitals.
- Octet Expansion: To form 5 covalent bonds, an atom must accommodate 10 electrons in its valence shell (expanded octet).
- Outcome: Phosphorus can promote an electron to the 3d orbital and form sp3d bonds. Nitrogen is strictly limited by the 'Octet Rule' and cannot form 5 bonds.
- Sterics: Additionally, Nitrogen is so small that having 5 large atoms around it would cause extreme steric repulsion.
This medium difficulty chemistry question is from the chapter chemical bonding and molecular structure, covering the topic of vsepr & hybridisation. It appeared in the 2025 exam.
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