How many stable Lewis resonance structures does the Nitrate ion ( NO3 _ ) have? 3 2 4
The Correct Answer and Explanation is:
Correct Answer: 3
The nitrate ion (NO₃⁻) has 3 stable Lewis resonance structures.
Explanation:
The nitrate ion consists of one nitrogen atom centrally bonded to three oxygen atoms. The ion carries a -1 overall charge. To determine the number of resonance structures, we must consider how the electrons can be arranged around the nitrogen and oxygen atoms while following the rules of covalent bonding and achieving full octets.
Step 1: Count valence electrons
- Nitrogen (N) has 5 valence electrons.
- Each oxygen (O) atom has 6 valence electrons.
- There are 3 oxygen atoms: 3 × 6 = 18 electrons.
- The ion carries a -1 charge, which means we add 1 more electron.
Total valence electrons = 5 + 18 + 1 = 24 electrons
Step 2: Draw a skeletal structure
The central nitrogen atom is single-bonded to each of the three oxygen atoms.
Step 3: Distribute electrons to complete octets
After placing single bonds (which account for 6 electrons), 18 electrons remain. These are distributed to give all atoms full octets. However, to minimize formal charges and properly represent the bonding, one of the nitrogen-oxygen bonds should be a double bond.
Step 4: Draw resonance structures
There are three possible ways to place the double bond between nitrogen and one of the three oxygen atoms. Each oxygen can, in turn, form a double bond with nitrogen while the other two remain single-bonded and carry a negative formal charge.
Therefore, there are 3 resonance structures, each showing the double bond in a different position.
Summary:
- Nitrate ion has 3 resonance structures
- Each structure has one N=O double bond and two N–O single bonds
- The actual structure is a hybrid, with bond lengths between those of single and double bonds
This delocalization of electrons contributes to the stability of the nitrate ion.
