Which of the following is the best Lewis structure for the nitrate ion, NO3^-?

• A. A central N atom triple-bonded to one O atom and single-bonded to two O atoms, with no formal charges.
• B. A central N atom double-bonded to one O atom and single-bonded to two O atoms, each single-bonded O atom bearing a negative formal charge; all atoms have complete octets.
• C. A central N atom single-bonded to three O atoms, each O atom bearing a negative formal charge; all atoms have complete octets.
• D. A central N atom double-bonded to all three O atoms, with no formal charges.

Answer: (B)

Verified step by step guidance

1. Step 1: Determine the total number of valence electrons available for the nitrate ion (NO3^-). Nitrogen has 5 valence electrons, each oxygen has 6, and the ion has an extra electron due to the negative charge. Calculate the sum: \$5 + 3 \times 6 + 1$.
2. Step 2: Draw a skeletal structure with nitrogen as the central atom bonded to three oxygen atoms. Connect each oxygen to nitrogen with single bonds initially.
3. Step 3: Distribute the remaining valence electrons as lone pairs on the oxygen atoms to complete their octets. Remember that each bond counts as 2 electrons.
4. Step 4: Check the formal charges on each atom using the formula: \(\text{Formal charge} = \text{Valence electrons} - \text{Nonbonding electrons} - \frac{1}{2} \times \text{Bonding electrons}\). Adjust bonds (e.g., form double bonds) to minimize formal charges and ensure all atoms have complete octets.
5. Step 5: Compare the possible Lewis structures by their formal charges and octet completion. The best Lewis structure will have formal charges minimized and placed on the most electronegative atoms, with all atoms having complete octets.