Which of the following Lewis dot structures best represents the nitrate ion, NO_3^-?

• A. A central nitrogen atom bonded to three oxygen atoms, all with double bonds, and no formal charges on any atom.
• B. A central nitrogen atom bonded to three oxygen atoms, all with single bonds, and the nitrogen atom carrying a negative formal charge.
• C. A central nitrogen atom bonded to two oxygen atoms with double bonds and one oxygen atom with a single bond, with the nitrogen atom carrying a positive formal charge.
• D. A central nitrogen atom bonded to three oxygen atoms, with one double bond and two single bonds, and each singly bonded oxygen carrying a negative formal charge. All atoms have complete octets.

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 extra negative charge adds 1 more electron. So, total electrons = 5 + (3 × 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 to satisfy the octet rule for the oxygen atoms first, placing lone pairs on oxygens to complete their octets.
4. Step 4: Check the formal charges on each atom. To minimize formal charges and satisfy the octet rule, convert one of the nitrogen-oxygen single bonds into a double bond. This reduces the formal charge on nitrogen and one oxygen.
5. Step 5: Confirm that the final Lewis structure has one nitrogen-oxygen double bond, two nitrogen-oxygen single bonds, with the singly bonded oxygens carrying negative formal charges, nitrogen carrying a positive formal charge, and all atoms having complete octets.