Which Lewis structure for OCN1- has a formal charge of -1 on the most electronegative atom?
The correct answer and explanation is:
Correct Lewis Structure for OCN⁻ with Formal Charge of -1 on the Most Electronegative Atom
The correct Lewis structure of the cyanate ion (OCN⁻) that places a formal charge of -1 on oxygen (O), the most electronegative atom, is:
Structure:
O=C=N⁻
Formal Charge Calculation
Formal charge is calculated using the formula: Formal Charge=(Valence Electrons)−(Non-Bonding Electrons)−Bonding Electrons2\text{Formal Charge} = (\text{Valence Electrons}) – (\text{Non-Bonding Electrons}) – \frac{\text{Bonding Electrons}}{2}
Step 1: Count Valence Electrons
- Oxygen (O): 6 valence electrons
- Carbon (C): 4 valence electrons
- Nitrogen (N): 5 valence electrons
- Total electrons available: 6+4+5+1=166 + 4 + 5 + 1 = 16 (extra electron from the -1 charge)
Step 2: Lewis Structure with Formal Charges
- Single Bond Configuration (O-C≡N⁻)
- Oxygen: 6 valence electrons (6 lone pair electrons, 2 bonding electrons)
- Carbon: 4 valence electrons (0 lone pairs, 4 bonding electrons)
- Nitrogen: 5 valence electrons (2 lone pair electrons, 6 bonding electrons)
- Oxygen: 6−6−22=−16 – 6 – \frac{2}{2} = -1
- Carbon: 4−0−82=04 – 0 – \frac{8}{2} = 0
- Nitrogen: 5−2−62=05 – 2 – \frac{6}{2} = 0
Since oxygen is the most electronegative element in OCN⁻, it is most stable with the negative charge (-1).
Explanation
The cyanate ion (OCN⁻) consists of oxygen, carbon, and nitrogen. When drawing its Lewis structure, we must satisfy the octet rule for each atom while ensuring the most stable distribution of formal charges.
Since oxygen (O) is the most electronegative element in this ion, the most stable Lewis structure should place the -1 formal charge on oxygen rather than on carbon or nitrogen. To achieve this, the best structure has a single bond between oxygen and carbon, and a triple bond between carbon and nitrogen (O-C≡N⁻).
Why This Structure is the Best?
- Electronegativity Consideration
- Oxygen (3.5) is more electronegative than nitrogen (3.0) and carbon (2.5), meaning it more readily accepts a negative charge.
- Formal Charge Stability
- The oxygen atom gets the -1 charge, keeping the carbon and nitrogen atoms neutral, leading to a more stable structure.
- Octet Rule Compliance
- All atoms have complete octets in this configuration.
This structure ensures maximum stability while following the rules of formal charge minimization and electronegativity considerations.
Now, I’ll generate an image of the correct Lewis structure for OCN⁻ with formal charge distribution.
Here is the Lewis structure of the cyanate ion (OCN⁻), showing the correct formal charges with a single bond between oxygen and carbon and a triple bond between carbon and nitrogen. Let me know if you need any modifications or further explanations!
