Covalent Bond

Question

The formal charge on the nitrogen atom in the nitrate ion (NO₃⁻) is:

RankGuru · Accepted Answer

1. **Draw the Lewis Structure of NO₃⁻**: Nitrogen is the central atom bonded to three oxygen atoms. One N=O double bond and two N–O single bonds (with negative formal charges on the singly-bonded oxygens) is one resonance structure. Total valence electrons = $5 + 3(6) + 1 = 24$.
2. **Apply the Formal Charge Formula**: $FC = V - N - \frac{B}{2}$, where V = valence electrons of free atom, N = non-bonding electrons, B = bonding electrons.
3. **Calculate for Nitrogen** (in the resonance structure with one double bond and two single bonds):
   - V = 5 (nitrogen has 5 valence electrons)
   - N = 0 (nitrogen has no lone pairs in this structure)
   - B = 8 (four bonds: one double + two single = 2 + 2 + 2 + 2 shared electrons)
   - $FC = 5 - 0 - \frac{8}{2} = 5 - 0 - 4 = +1$.
4. **Verify Charge Balance**: In each resonance structure, the doubly-bonded O has FC = 0, each singly-bonded O has FC = −1. Total: $(+1) + 0 + (-1) + (-1) = -1$, which matches the overall charge of NO₃⁻.
5. **Conclusion**: The formal charge on nitrogen in NO₃⁻ is **+1**, despite nitrogen being bonded to more electronegative oxygen atoms. Formal charge is a bookkeeping tool and does not represent actual electron density.

Covalent Bond

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