The formal charge of phosphorus in PCl₅ is 0, while its oxidation state is +5.
Formal Charge Calculation: Formal charge = V - N - B/2
Where:
- V = valence electrons of P = 5
- N = non-bonding electrons = 0
- B = bonding electrons = 10 (5 bonds × 2 electrons)
Formal charge = 5 - 0 - 10/2 = 5 - 0 - 5 = 0
Oxidation State: Each Cl is more electronegative than P, so:
- Each P-Cl bond assigns both electrons to Cl
- P loses 5 electrons (one per bond)
- Oxidation state of P = +5
Important Distinction:
- Formal charge: 0 (electron bookkeeping assuming equal sharing)
- Oxidation state: +5 (considering electronegativity differences)
Key Takeaways:
- Formal charge ≠ oxidation state
- Formal charge of P in PCl₅ = 0
- Oxidation state of P in PCl₅ = +5
- Both concepts serve different purposes in chemistry