A student proposes the following Lewis structure for the nitronium NO2+ ion. =N= Assign formal charge to each atom in the student’s Lewis structure. atom formal charge left 0 N right 0
The Correct Answer and Explanation is:
Correct Answer:
| atom | formal charge |
| left O | 0 |
| N | +1 |
| right O | 0 |
Explanation:
To assign a formal charge to each atom in the Lewis structure, we use the following formula:
Formal Charge = (Valence Electrons) – (Non-bonding Electrons) – (1/2 * Bonding Electrons)
First, we determine the number of valence electrons for each element from its position on the periodic table. Oxygen (O) is in Group 16, so it has 6 valence electrons. Nitrogen (N) is in Group 15, so it has 5 valence electrons.
1. Left Oxygen Atom:
In the provided structure, the left oxygen atom has 4 non-bonding electrons (two lone pairs) and participates in a double bond with nitrogen, which contains 4 bonding electrons.
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- Formal Charge = 6 – 4 – ½(4) = 6 – 4 – 2 = 0
2. Central Nitrogen Atom:
- Valence electrons for N = 5
- Non-bonding electrons = 0 (there are no lone pairs on the nitrogen atom)
- Bonding electrons = 8 (from two double bonds, one to each oxygen atom)
- Formal Charge = 5 – 0 – ½(8) = 5 – 4 = +1
3. Right Oxygen Atom:
- This atom is structurally identical to the left oxygen atom.
- Valence electrons for O = 6
- Non-bonding electrons = 4 (from two lone pairs)
- Bonding electrons = 4 (from the double bond)
- Formal Charge = 6 – 4 – ½(4) = 6 – 4 – 2 = 0
Finally, we can check our work. The sum of the formal charges of all atoms in an ion must equal the overall charge of the ion. In this case, the sum is 0 (for the left O) + (+1) (for N) + 0 (for the right O) = +1. This matches the +1 charge of the nitronium ion, confirming our assignments are correct.Formal Charge = 6 (valence) – 4 (non-bonding) – (1/2 * 4) (bonding)
- Formal Charge = 6 – 4 – 2 = 0
2. Central Nitrogen Atom:
The central nitrogen atom has no non-bonding electrons (no lone pairs). It forms two double bonds, one with each oxygen atom, for a total of 8 bonding electrons.
- Formal Charge = 5 (valence) – 0 (non-bonding) – (1/2 * 8) (bonding)
- Formal Charge = 5 – 0 – 4 = +1
3. Right Oxygen Atom:
The right oxygen atom is structurally identical to the left one. It has 4 non-bonding electrons and 4 bonding electrons from its double bond with nitrogen.
- Formal Charge = 6 (valence) – 4 (non-bonding) – (1/2 * 4) (bonding)
- Formal Charge = 6 – 4 – 2 = 0
As a final check, the sum of all formal charges in the ion should equal its
