Question

In NO₃⁻ ion, the number of bond pairs and lone pairs of electrons on nitrogen atom are

• A. 2, 2
• B. 3, 1
• C. 1, 3
• D. 4, 0

Hint:

Key Exam Tip:
For resonance structures, consider one valid Lewis structure to determine hybridization and formal charges. Nitrogen in $\text{NO}_3^-$ forms 4 electron groups (bonds) around it, indicating 4 bond pairs and 0 lone pairs.

Answer 1

The Correct Option is D

To find the bond pairs and lone pairs on the nitrogen atom in $\text{NO}_3^-$, we draw its Lewis structure.
1. Total valence electrons: N (5) + 3×O (6) + charge (1) = 5 + 18 + 1 = 24.
2. Central atom is N. Connect N to 3 O atoms with single bonds (uses 6 electrons).
3. Distribute remaining 18 electrons as lone pairs on O atoms to satisfy their octets (3 lone pairs per O, $3 \times 6 = 18$ electrons).
4. Check octet for N: N currently has only 6 electrons (3 single bonds).
5. Form a double bond by moving one lone pair from an oxygen to form a double bond with N. This gives N an octet. In $\text{NO}_3^-$, resonance occurs, and the structure has one N=O bond and two N-O single bonds, or an average bond order.
6. Focusing on the nitrogen atom: it forms two single bonds and one double bond. Each single bond contributes one bond pair, and the double bond contributes two bond pairs. Thus, N has $1 + 1 + 2 = 4$ bond pairs.
7. Nitrogen has no lone pairs of electrons in this structure.
So, there are 4 bond pairs and 0 lone pairs on the nitrogen atom.
Final Answer: \(\boxed{D}\)