Draw Lewis structure(s) showing all possible equivalent resonance forms for the nitronium ion ( NO2+ ). Draw one structure per sketcher box, and separate any added sketcher boxes with the ↔ symbol. Do NOT show any ion charges in your drawings. Do not draw double bonds to oxygen unless they are needed for the central atom to obey the octet rule. NO2+ :
part b.) What is the bond order of the N – O bonds in the nitrite ion ? (enter a decimal number)
In which species (NO2- or NO2+) are the N-O bond(s) longer? _________nitrite ionnitronium ion
In which species (NO2- or NO2+) are the N-O bond(s) weaker? _________nitrite ionnitronium ion
The correct answer and explanation is :
Part A: Lewis Structures of NO₂⁺ (Nitronium Ion)
The nitronium ion (NO₂⁺) consists of a central nitrogen atom bonded to two oxygen atoms. To determine the resonance structures:
- Valence Electrons Calculation:
- Nitrogen (N) has 5 valence electrons.
- Oxygen (O) has 6 valence electrons × 2 = 12.
- The ion has a +1 charge, meaning 1 electron is lost.
- Total valence electrons = 5 + 12 – 1 = 16.
- Drawing the Lewis Structure:
- Place nitrogen in the center with two oxygens attached.
- To satisfy the octet rule, nitrogen forms two double bonds (N=O) with oxygen.
- There are no lone pairs on nitrogen.
- Each oxygen has two lone pairs.
- The formal charge on nitrogen is +1, and both oxygens have 0 formal charge.
- The molecule is linear (180° bond angle).
- Resonance Structures:
Since both N=O bonds are equivalent, the two resonance structures are: O=N⁺=O ↔ O=N⁺=O The resonance structures are identical because of the symmetrical arrangement.
Part B: Bond Order of N-O Bonds in NO₂⁻ (Nitrite Ion)
The nitrite ion (NO₂⁻) has one double bond (N=O) and one single bond (N–O) in resonance.
- Bond order formula:
[
\text{Bond Order} = \frac{\text{Total Number of Bonds}}{\text{Total Resonance Structures}}
]
Since nitrite has two resonance structures where the single and double bonds alternate: [
\text{Bond Order} = \frac{1 + 2}{2} = 1.5
] Bond Order of N–O in NO₂⁻ = 1.5.
Part C: Comparing Bond Length and Strength
- Which species has longer N-O bonds?
Answer: Nitrite ion (NO₂⁻)
- The higher the bond order, the shorter the bond.
- In NO₂⁺, the bond order is 2.0 (pure double bonds).
- In NO₂⁻, the bond order is 1.5 (between single and double bonds).
- Since NO₂⁻ has a lower bond order, it has longer bonds.
- Which species has weaker N-O bonds?
Answer: Nitrite ion (NO₂⁻)
- Stronger bonds have higher bond order.
- Since NO₂⁺ has bond order 2.0, its bonds are stronger.
- NO₂⁻ has bond order 1.5, meaning its bonds are weaker.
Explanation (300 Words)
The nitronium ion (NO₂⁺) is a linear molecule with two equivalent N=O double bonds, making it highly symmetrical. Because nitrogen has no lone pairs, it achieves a formal charge of +1, while both oxygens have a formal charge of 0. This results in a bond order of 2.0, meaning the N–O bonds are purely double bonds.
In contrast, the nitrite ion (NO₂⁻) is bent due to the presence of one lone pair on nitrogen. It has one single bond and one double bond, but because of resonance, both bonds are delocalized and effectively have an intermediate bond order of 1.5.
Bond length and bond strength are directly related to bond order:
- Higher bond order → Shorter, Stronger Bonds.
- Lower bond order → Longer, Weaker Bonds.
Since the nitronium ion (NO₂⁺) has a bond order of 2.0, its bonds are shorter and stronger than those in nitrite (NO₂⁻), which has a bond order of 1.5. This means that the N-O bonds in NO₂⁻ are longer and weaker compared to NO₂⁺.
These differences in bonding affect chemical reactivity:
- NO₂⁺ is an electrophile, often found in nitration reactions (e.g., electrophilic aromatic substitution).
- NO₂⁻ is a stable anion and acts as a Lewis base in coordination chemistry.
In summary:
- NO₂⁺ (Nitronium ion) has shorter, stronger bonds (bond order = 2.0).
- NO₂⁻ (Nitrite ion) has longer, weaker bonds (bond order = 1.5).