For the Lewis structure of OCN, you should take formal charges into account to find the best Lewis structure for the molecule.

For the Lewis structure of OCN, you should take formal charges into account to find the best Lewis structure for the molecule. Assign formal charges above each atom in each structure and select the best Lewis structure. (12) Formal Charges: O-C=N: :0-C-N: :O=C-N: Explain your selection for the best choice_
VIII The cyanate ion, OCN, has three resonance structures shown below. For the Lewis structure of OCN, you should take formal charges into account to find the best Lewis structure for the molecule. Assign formal charges above each atom in each structure and select the best Lewis structure. (12) Formal Charges: O-C=N: :0-C-N: :O=C-N: Explain your selection for the best choice_

The Correct Answer and Explanation is:

Resonance Structures:

1. O–C≡N⁻
2. ⁻O–C≡N
3. O=C=N⁻

Let’s assign formal charges to each atom in these structures.
(Recall: Formal charge = [valence electrons] – [non-bonding electrons] – [1/2 bonding electrons])

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Structure 1: O–C≡N⁻

• Oxygen (O): 6 valence e⁻ – 6 nonbonding e⁻ – 1 bond = –1
• Carbon (C): 4 valence e⁻ – 0 lone pairs – 4 bonds = 0
• Nitrogen (N): 5 valence e⁻ – 2 nonbonding e⁻ – 3 bonds = 0

Formal Charges:
O (–1)  C (0)  N (0)

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Structure 2: ⁻O–C≡N

• Oxygen (O): 6 valence e⁻ – 6 nonbonding e⁻ – 1 bond = –1
• Carbon (C): 4 valence e⁻ – 0 lone pairs – 4 bonds = 0
• Nitrogen (N): 5 valence e⁻ – 0 lone pairs – 4 bonds = +1

Formal Charges:
O (–1)  C (0)  N (+1)

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Structure 3: O=C=N⁻

• Oxygen (O): 6 valence e⁻ – 4 nonbonding e⁻ – 2 bonds = 0
• Carbon (C): 4 valence e⁻ – 0 lone pairs – 4 bonds = 0
• Nitrogen (N): 5 valence e⁻ – 4 nonbonding e⁻ – 1 bond = –1

Formal Charges:
O (0)  C (0)  N (–1)

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Best Lewis Structure: O=C=N⁻

This structure is the most stable because:

1. All atoms have formal charges as close to zero as possible.
2. The negative charge is on the more electronegative atom (nitrogen), which is preferred.
3. There is no formal charge separation, unlike Structure 2 where both a negative and positive formal charge appear.

Thus, based on formal charge minimization and electronegativity considerations, O=C=N⁻ is the best Lewis structure for the cyanate ion (OCN⁻). This structure contributes most to the resonance hybrid and represents the most stable configuration of electrons for the ion.