To determine the dominant resonance structure for NOCl (nitrosyl chloride), we need to calculate the formal charges for each atom in the possible resonance structures. The structure with the lowest formal charges and the negative charge on the most electronegative atom is usually the dominant one.
Step 1: Draw the Lewis Structures
NOCl has three possible resonance structures:
-
Structure 1: N is double-bonded to O and single-bonded to Cl.
N=O-Cl
-
Structure 2: N is single-bonded to O and double-bonded to Cl.
N-O=Cl
-
Structure 3: N is triple-bonded to O and single-bonded to Cl.
N≡O-Cl
Step 2: Calculate Formal Charges
The formal charge is calculated using the formula:
Formal Charge = Valence Electrons – (Non-bonding Electrons + 1/2 Bonding Electrons)
Structure 1: N=O-Cl
- N: 5 – (2 + 4/2) = 0
- O: 6 – (4 + 4/2) = 0
- Cl: 7 – (6 + 2/2) = 0
Structure 2: N-O=Cl
- N: 5 – (2 + 4/2) = 0
- O: 6 – (6 + 2/2) = -1
- Cl: 7 – (4 + 4/2) = +1
Structure 3: N≡O-Cl
- N: 5 – (1 + 6/2) = +1
- O: 6 – (2 + 6/2) = -1
- Cl: 7 – (6 + 2/2) = 0
Step 3: Determine the Dominant Structure
Based on the formal charges:
- Structure 1 has all formal charges equal to zero, which is ideal.
- Structure 2 has a negative charge on O and a positive charge on Cl, which is less favorable.
- Structure 3 has a positive charge on N and a negative charge on O, which is also less favorable.
Therefore, Structure 1 (N=O-Cl) is the dominant resonance structure for NOCl.