Which of the following is the correct Lewis dot structure for the isocyanate ion, OCN^-?

• A. O with two lone pairs, single bond to C, double bond to N with three lone pairs; overall negative charge on N
• B. O with one lone pair, double bond to C, double bond to N with two lone pairs; overall negative charge on C
• C. O with two lone pairs, triple bond to C, single bond to N with two lone pairs; overall negative charge on N
• D. O with three lone pairs, single bond to C, triple bond to N with one lone pair; overall negative charge on O

Answer: (C)

Verified step by step guidance

1. Step 1: Determine the total number of valence electrons for the isocyanate ion (OCN⁻). Oxygen has 6 valence electrons, carbon has 4, nitrogen has 5, and the negative charge adds 1 extra electron. So, total valence electrons = 6 + 4 + 5 + 1 = 16 electrons.
2. Step 2: Arrange the atoms in a reasonable skeletal structure. For OCN⁻, the common arrangement is O–C–N, with carbon in the center because it can form multiple bonds easily.
3. Step 3: Distribute electrons to satisfy the octet rule for each atom, starting by placing single bonds between atoms (each bond counts as 2 electrons), then add lone pairs to complete octets. Remember to account for the total 16 valence electrons.
4. Step 4: Consider multiple bonding (double or triple bonds) to ensure all atoms have complete octets and the total number of electrons matches 16. Adjust bonds between O, C, and N accordingly.
5. Step 5: Assign formal charges to each atom using the formula: \(\text{Formal charge} = \text{Valence electrons} - \text{Nonbonding electrons} - \frac{1}{2} \times \text{Bonding electrons}\). The best Lewis structure minimizes formal charges and places the negative charge on the most electronegative atom.