Based on formal charges, which of the following is the best Lewis electron-dot diagram for the nitrate ion, NO_3^-?

• A. A structure with three single bonds between N and each O atom, and a formal charge of +2 on N and -1 on each O.
• B. A structure with one triple bond between N and one O, and two single bonds to the other O atoms, with formal charges of -2 on N and +1 on the triply bonded O.
• C. A structure with three double bonds between N and each O atom, with all atoms having a formal charge of 0.
• D. A structure with one double bond between N and one O, and two single bonds to the other O atoms, with formal charges of +1 on N and -1 on each singly bonded O.

Answer: (D)

Verified step by step guidance

1. Step 1: Determine the total number of valence electrons available for the nitrate ion (NO_3^-). Nitrogen has 5 valence electrons, each oxygen has 6, and the ion has an extra electron due to the negative charge. Calculate the total as: \$5 + 3 \times 6 + 1$.
2. Step 2: Draw a skeletal structure with nitrogen as the central atom bonded to three oxygen atoms. Initially, connect each oxygen to nitrogen with a single bond.
3. Step 3: Distribute the remaining valence electrons to complete the octets of the oxygen atoms first, then place any leftover electrons on nitrogen.
4. Step 4: Calculate the formal charges for each atom using the formula: \(\text{Formal charge} = \text{Valence electrons} - \text{Nonbonding electrons} - \frac{1}{2} \times \text{Bonding electrons}\). This helps identify if the structure is reasonable.
5. Step 5: Adjust the bonding by converting one of the N–O single bonds to a double bond to reduce formal charges, aiming for the structure where nitrogen has a +1 formal charge, the double-bonded oxygen has 0, and the singly bonded oxygens have -1 each, which matches the best Lewis structure for NO_3^-.