Draw the Lewis Dot Structure for the nitrite anion, NO2- : 2. Does the nitrite ion above have more than one resonance structure? [ Yes / No ] 3. Using your VSEPR table, determine the molecular shape and ideal bond angle of this ion. Molecular Shape
The Correct Answer and Explanation is:
Lewis Dot Structure for the Nitrite Anion (NO₂⁻)
To draw the Lewis structure of the nitrite anion (NO₂⁻), follow these steps:
- Step 1: Count the total number of valence electrons:
- Nitrogen (N) is in group 15, so it has 5 valence electrons.
- Each oxygen (O) is in group 16, so each oxygen has 6 valence electrons.
- The negative charge indicates an extra electron, so add 1 electron.
- Total electrons = 5 (N) + 2(6 for each O) + 1 (for the negative charge) = 18 valence electrons.
- Step 2: Arrange the atoms:
- Nitrogen is the central atom, with two oxygen atoms bonded to it.
- Step 3: Create bonds:
- Start by drawing single bonds between nitrogen and each oxygen atom. This uses 4 electrons (2 electrons per bond).
- Step 4: Fill in the lone pairs:
- After drawing the bonds, the remaining 14 electrons are used to complete the octets of the oxygen atoms. Each oxygen will have 6 more electrons to satisfy the octet rule (since the O atoms already share 2 electrons with N via the bond).
- Step 5: Check if the nitrogen atom satisfies the octet rule:
- Nitrogen will have only 4 electrons from the bonds, so it needs 4 more to complete its octet. To achieve this, you will convert one lone pair from an oxygen into a second bond with nitrogen.
- Step 6: Finalize the structure:
- You end up with one double bond between nitrogen and one oxygen, and a single bond between nitrogen and the other oxygen, with one lone pair on each oxygen.
The Lewis structure would look like this:
mathematicaCopyEdit O
||
N ← (with a lone pair)
O⁻
2. Does the nitrite ion have more than one resonance structure?
Yes, the nitrite ion has more than one resonance structure. There are two possible resonance forms in which the position of the double and single bonds between nitrogen and the oxygen atoms can be swapped, while maintaining the overall charge distribution.
- In one resonance structure, nitrogen is double-bonded to one oxygen and single-bonded to the other oxygen (which has a negative charge).
- In the other resonance structure, the positions of the double and single bonds are reversed.
This indicates that the nitrite ion does not have a fixed arrangement but rather a resonance hybrid where the electrons are delocalized.
3. Molecular Shape and Bond Angles
Using the VSEPR (Valence Shell Electron Pair Repulsion) theory, the shape of the nitrite ion (NO₂⁻) can be determined:
- Electron domains: There are two bonding pairs of electrons (one from each oxygen) and one lone pair on nitrogen. This gives three electron domains around the nitrogen atom.
- Molecular geometry: With three electron domains, the molecular shape of the nitrite ion is bent (similar to the structure of water).
- Bond angles: The ideal bond angle for a bent molecule is approximately 120°, although the exact bond angle can be slightly less due to the lone pair of electrons which repels the bonding pairs slightly more.
Explanation:
The VSEPR model predicts that the lone pair on nitrogen will push the two oxygen atoms closer together, resulting in a bent shape. This shape minimizes the repulsion between the electron pairs, ensuring the most stable configuration. The bond angles in the bent configuration are typically slightly less than 120°, as the lone pair exerts more repulsion compared to bonding pairs.
