Phosphorus commonly exhibits valencies of 3 and 5, depending on its bonding state and the compound formed.
Variable Valency of Phosphorus:
Valency 3 (Common):
- Compounds: PCl₃, PH₃, P₂O₃
- Uses three unpaired p-electrons
- Ground state configuration
- Example: PH₃ (phosphine)
Valency 5 (Common):
- Compounds: PCl₅, P₂O₅, H₃PO₄
- Uses expanded octet with d-orbitals
- Excited state configuration
- Example: PCl₅ (phosphorus pentachloride)
Electronic Basis:
- Ground state: 3s² 3p³ (3 unpaired electrons)
- Excited state: 3s¹ 3p³ 3d¹ (5 unpaired electrons)
- Period 3 element: can expand beyond octet
Key Takeaways:
- Most common valencies: 3 and 5
- Valency 3: lower oxidation states
- Valency 5: higher oxidation states, d-orbital involvement
- Variable valency due to available d-orbitals