Show the possible resonance structures for nitrous oxide, N2O (the central atom is nitrogen). Indicate nonzero formal charges where they are present. Which resonance structure gives the best representation of this molecule?
The Correct Answer and Explanation is:
To draw the possible resonance structures of nitrous oxide (N₂O), where the central atom is nitrogen, we need to consider the bonding and the formal charges in the molecule. N₂O is composed of two nitrogen atoms and one oxygen atom, and the central atom, as per the question, is nitrogen.
Possible Resonance Structures:
- First Structure:
- The molecule consists of a N=N=O bond. The first nitrogen atom (leftmost) has a single bond to the second nitrogen, which in turn has a double bond to oxygen.
- Formal charges: The leftmost nitrogen (N) has a formal charge of +1, and the oxygen (O) has a formal charge of -1.
- The second nitrogen (central nitrogen) has no formal charge.
- Second Structure:
- The molecule consists of a N≡N–O bond, where the first nitrogen (leftmost) is triple-bonded to the second nitrogen, and the second nitrogen is single-bonded to oxygen.
- Formal charges: The leftmost nitrogen (N) has no formal charge, and the oxygen (O) has a formal charge of -1. The second nitrogen (N) now has a +1 formal charge.
- Third Structure:
- The molecule consists of a N=N–O with lone pairs, where the oxygen atom is double-bonded to the second nitrogen, and there are lone pairs on nitrogen.
- Formal charges: The first nitrogen (N) has a formal charge of +1, while the oxygen (O) has a formal charge of -1.
Best Representation of N₂O:
Among the resonance structures, the second structure is the most stable and gives the best representation of N₂O. Here’s why:
- It minimizes the formal charges across the atoms. The left nitrogen (N) has no charge, and the right nitrogen (N) carries a +1 charge while the oxygen (O) has a -1 charge, which is more favorable compared to the other two structures.
- In general, the most stable resonance structure is the one where the formal charges are minimized and spread as evenly as possible across the atoms.
This resonance structure better reflects the actual bonding in N₂O, which has a linear molecular shape and bond order close to 2 for the N-N bond and 2 for the N-O bond, consistent with the experimental data on bond lengths.
