Which of the following best represents the resonance hybrid of the nitrate ion (NO_3^-)?

• A. A structure with two double bonds and one single bond, with negative charge on the nitrogen atom.
• B. A structure with three equivalent N–O bonds and the negative charge delocalized over all three oxygen atoms.
• C. A structure with three single bonds and the negative charge localized on the nitrogen atom.
• D. A structure with one double bond and two single bonds, with negative charge localized on one oxygen atom.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand what a resonance hybrid represents. It is a structure that shows the delocalization of electrons across multiple atoms, combining all resonance forms into one depiction where bonds and charges are spread out rather than localized.
2. Step 2: Recall the Lewis structure of the nitrate ion (NO_3^-). It has one nitrogen atom bonded to three oxygen atoms, with an overall negative charge. The nitrogen typically forms bonds with the oxygens, and the negative charge is distributed among the oxygens.
3. Step 3: Consider the resonance structures of NO_3^-. There are multiple valid Lewis structures where the double bond between nitrogen and oxygen shifts among the three oxygen atoms, and the negative charge moves accordingly. This means no single bond or charge is fixed on one atom.
4. Step 4: The resonance hybrid is best represented by showing three equivalent N–O bonds of equal length and strength, indicating partial double bond character in all three bonds, and the negative charge is delocalized over all three oxygen atoms rather than localized on one atom.
5. Step 5: Therefore, the correct resonance hybrid structure is the one with three equivalent N–O bonds and the negative charge delocalized over all three oxygen atoms, reflecting the true electronic structure of the nitrate ion.