In the POF
molecule, the P atom is the central atom. a Draw a Lewis diagram for POF
in which all atoms have a formal charge of zero. b Draw a Lewis structure for POF
in which the octet rule is satisfied on all atoms and show all NONZERO formal charges on all atoms. c Based on formal charge, which is the best Lewis structure for the molecule?
In the POF
molecule, the P atom is the central atom. a Draw a Lewis diagram for POF
in which all atoms have a formal charge of zero. b Draw a Lewis structure for POF
in which the octet rule is satisfied on all atoms and show all NONZERO formal charges on all atoms. c Based on formal charge, which is the best Lewis structure for the molecule?
The Correct Answer and Explanation is:
Lewis Structure of POF (Phosphoryl Fluoride)
The molecule POF (phosphoryl fluoride) consists of phosphorus (P), oxygen (O), and fluorine (F), with phosphorus as the central atom.
a. Lewis diagram with formal charges of zero on all atoms
To achieve zero formal charges, phosphorus forms a double bond with oxygen and a single bond with fluorine:
..
O=P—F
..
- Oxygen has 2 lone pairs and is double bonded to P.
- Fluorine has 3 lone pairs and is single bonded to P.
- Phosphorus uses 10 valence electrons (an expanded octet is allowed for P).
Formal charge calculation:
- O: 6 valence − (4 non-bonding + 2 bonding) = 0
- F: 7 valence − (6 non-bonding + 1 bonding) = 0
- P: 5 valence − (0 non-bonding + 5 bonding) = 0
✅ All atoms have formal charge = 0
b. Lewis structure satisfying the octet rule on all atoms
To satisfy the octet rule (only 8 electrons around each atom), P must form only single bonds:
..
O–P–F
..
- Each atom obeys the octet rule (O and F with 3 lone pairs, P with two single bonds and one lone pair).
Formal charge calculation:
- O: 6 valence − (6 non-bonding + 1 bonding) = −1
- F: 7 valence − (6 non-bonding + 1 bonding) = 0
- P: 5 valence − (2 non-bonding + 2 bonding) = +1
So, the structure has:
- O: −1
- P: +1
- F: 0
c. Best Lewis structure based on formal charge
The best structure minimizes formal charges and places negative charges on the most electronegative atoms. Structure (a) has zero formal charges and allows phosphorus to expand its octet (which is valid for third-period elements like P). Structure (b) satisfies the octet rule but introduces nonzero formal charges (+1 on P, −1 on O), making it less stable.
✅ Conclusion:
Structure (a) — with a double bond between P and O and no formal charges — is the best Lewis structure for POF.
