Answer :
Final answer:
The best Lewis structure for the nitrate anion (NO3-) includes a nitrogen center atom connected to three oxygen atoms, with one double bond and a delocalized negative charge. The nitrogen atom carries a +1 formal charge in this structure.
Explanation:
To draw the best Lewis structure for the nitrate anion (NO3-), we first count up the valence electrons, which are (1×5) from the nitrogen atom, (3×6) from the three oxygen atoms, plus an additional electron because of the negative charge, totaling 24 electrons. In the Lewis structure, nitrogen is in the center connected to three oxygen atoms. One of the oxygen atoms will form a double bond with the nitrogen, while the others will have single bonds. The negative charge is delocalized among the oxygen atoms through resonance, which means the actual molecule is an average of the three resonance structures.
When we determine the formal charges for the atoms in the nitrate ion, we find that when nitrogen has one double bond with an oxygen and two single bonds with the other oxygens, the most stable formal charge distribution is achieved. The formal charge on the nitrogen in each resonance structure is +1 on nitrogen (from 5 valence electrons normally, two lone pair electrons on the nitrogen, participating in one double and two single bonds), -1 on each singly bonded oxygen (from 6 valence electrons normally, participating in one single bond and carrying three lone pairs plus one extra electron due to the negative charge), and 0 on the double-bonded oxygen (from 6 valence electrons normally, participating in one double bond, and carrying two lone pairs). The overall charge of the ion remains at -1. Thus, nitrogen in the nitrate ion usually carries a +1 formal charge.
