Which of the following statements correctly describes the resonance structures of the nitrite ion, NO_2^-?

• A. NO_2^- does not exhibit resonance because all bonds are equivalent and there is no delocalization of electrons.
• B. NO_2^- has three major resonance structures, each with a different atom carrying the negative charge.
• C. NO_2^- has only one resonance structure, with both N–O bonds being single bonds and the negative charge localized on one oxygen atom.
• D. NO_2^- has two major resonance structures, each with one N–O single bond and one N=O double bond, with the negative charge delocalized over both oxygen atoms.

Answer: (D)

Verified step by step guidance

1. Recall that resonance structures are different Lewis structures for the same molecule that differ only in the placement of electrons, not the arrangement of atoms.
2. Draw the Lewis structure of the nitrite ion (NO_2^-), noting that nitrogen is the central atom bonded to two oxygen atoms, and the ion carries an overall negative charge.
3. Determine the total number of valence electrons: nitrogen contributes 5, each oxygen contributes 6, and there is one extra electron due to the negative charge, summing to 18 valence electrons.
4. Construct possible resonance structures by placing one N=O double bond and one N–O single bond in each structure, and then switch the positions of the double and single bonds between the two oxygens to generate two major resonance forms.
5. Recognize that the negative charge is delocalized over the two oxygen atoms because the resonance structures show the negative charge on different oxygens, which explains the equivalence of the N–O bonds in the actual ion.