Chapter 8, Problem 33PS

Three resonance structures are possible for dinitrogen monoxide, N₂O.

1. (a) Draw the three resonance structures.
2. (b) Calculate the formal charge on each atom in each resonance structure.
3. (c) Based on formal charges and electronegativity, predict which resonance structure is the most reasonable.

Interpretation Introduction

Interpretation:

The three resonance structure of $N_{2}O$ has to be drawn.

Concept Introduction:

Resonance structures: A molecule or ion which show more than structure but none of them are accurately correct show the known property of that molecule, and can lie between the canonical structure is known as resonance or canonical or contributing structure.

Explanation of Solution

The three resonance structure is drawn

Interpretation Introduction

Interpretation:

Formal charge on each atom in each resonance structure has to be calculated.

Concept Introduction:

Formal charge: It is the electrostatic charge that would reside on an atom in a molecule or polyatomic ion if all bonding electron are shared equally between pairs of atoms.

Formal charge calculation: The formal charge for atom in a molecule or ion is calculated based on the Lewis structure of the molecule or ion by following the given equation below:

- Number of valence electrons

- Number of non-bonding electrons

- Number of bonding electrons

Explanation of Solution

The formal charges can be calculated as follows.

For resonance structure A is given below,

Formal charge on nitrogen$1$ can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(1\right)=5\\ Numberofnon-bondingelectrons=4\\ Numberofbondingelectrons=4\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}\text{5}\text{-}4\text{-}\frac{4}{\text{2}}\\ \text{=}-1\end{array}$

Formal charge on nitrogen$2$ can be calculated as follows.

 $\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(2\right)=5\\ Numberofnon-bondingelectrons=0\\ Numberofbondingelectrons=8\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}5\text{-}0\text{-}\frac{8}{\text{2}}\\ \text{=}+1\end{array}$

Formal charge on oxygen can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonO=6\\ Numberofnon-bondingelectrons=4\\ Numberofbondingelectrons=4\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}6\text{-}4\text{-}\frac{4}{\text{2}}\\ \text{=}\text{0}\end{array}$

For resonance structure B is given below,

Formal charge on nitrogen$1$ can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(1\right)=5\\ Numberofnon-bondingelectrons=2\\ Numberofbondingelectrons=6\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}\text{5}\text{-}2\text{-}\frac{6}{\text{2}}\\ \text{=}0\end{array}$

Formal charge on nitrogen$2$ can be calculated as follows.

 $\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(2\right)=5\\ Numberofnon-bondingelectrons=0\\ Numberofbondingelectrons=8\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}5\text{-}0\text{-}\frac{8}{\text{2}}\\ \text{=}+1\end{array}$

Formal charge on oxygen can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonO=6\\ Numberofnon-bondingelectrons=6\\ Numberofbondingelectrons=2\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}6\text{-}6\text{-}\frac{2}{\text{2}}\\ \text{=}-1\end{array}$

For resonance structure C, is given below,

Formal charge on nitrogen$1$ can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(1\right)=5\\ Numberofnon-bondingelectrons=6\\ Numberofbondingelectrons=2\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}\text{5}\text{-}6\text{-}\frac{2}{\text{2}}\\ \text{=}-2\end{array}$

Formal charge on nitrogen$2$ can be calculated as follows.

 $\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(2\right)=5\\ Numberofnon-bondingelectrons=0\\ Numberofbondingelectrons=8\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}5\text{-}0\text{-}\frac{8}{\text{2}}\\ \text{=}+1\end{array}$

Formal charge on oxygen can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonO=6\\ Numberofnon-bondingelectrons=2\\ Numberofbondingelectrons=6\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}6\text{-}2\text{-}\frac{6}{\text{2}}\\ \text{=}+1\end{array}$

Interpretation Introduction

Interpretation:

From the resonance structure drawn, the most reasonable structure has to be identified.

Concept Introduction:

Formal charge: It is the electrostatic charge that would reside on an atom in a molecule or polyatomic ion if all bonding electron are shared equally between pairs of atoms.

Formal charge calculation: The formal charge for atom in a molecule or ion is calculated based on the Lewis structure of the molecule or ion by following the given equation below:

- Number of valence electrons

- Number of non-bonding electrons

- Number of bonding electrons

Resonance structures:

A molecule or ion which show more than structure but none of them are accurately correct show the known property of that molecule, and can lie between the canonical structure is known as resonance or canonical or contributing structure.

Explanation of Solution

The three resonance structure is drawn

1. (a) The formal charges can be calculated as follows.

For resonance structure A

Formal charge on nitrogen$1$ can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(1\right)=5\\ Numberofnon-bondingelectrons=4\\ Numberofbondingelectrons=4\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}\text{5}\text{-}4\text{-}\frac{4}{\text{2}}\\ \text{=}-1\end{array}$

Formal charge on nitrogen$2$ can be calculated as follows.

 $\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(2\right)=5\\ Numberofnon-bondingelectrons=0\\ Numberofbondingelectrons=8\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}5\text{-}0\text{-}\frac{8}{\text{2}}\\ \text{=}+1\end{array}$

Formal charge on oxygen can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonO=6\\ Numberofnon-bondingelectrons=4\\ Numberofbondingelectrons=4\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}6\text{-}4\text{-}\frac{4}{\text{2}}\\ \text{=}\text{0}\end{array}$

For resonance structure B

Formal charge on nitrogen$1$ can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(1\right)=5\\ Numberofnon-bondingelectrons=2\\ Numberofbondingelectrons=6\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}\text{5}\text{-}2\text{-}\frac{6}{\text{2}}\\ \text{=}0\end{array}$

Formal charge on nitrogen$2$ can be calculated as follows.

 $\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(2\right)=5\\ Numberofnon-bondingelectrons=0\\ Numberofbondingelectrons=8\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}5\text{-}0\text{-}\frac{8}{\text{2}}\\ \text{=}+1\end{array}$

Formal charge on oxygen can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonO=6\\ Numberofnon-bondingelectrons=6\\ Numberofbondingelectrons=2\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}6\text{-}6\text{-}\frac{2}{\text{2}}\\ \text{=}-1\end{array}$

For resonance structure C

Formal charge on nitrogen$1$ can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(1\right)=5\\ Numberofnon-bondingelectrons=6\\ Numberofbondingelectrons=2\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}\text{5}\text{-}6\text{-}\frac{2}{\text{2}}\\ \text{=}-2\end{array}$

Formal charge on nitrogen$2$ can be calculated as follows.

 $\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonN\left(2\right)=5\\ Numberofnon-bondingelectrons=0\\ Numberofbondingelectrons=8\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}5\text{-}0\text{-}\frac{8}{\text{2}}\\ \text{=}+1\end{array}$

Formal charge on oxygen can be calculated as follows.

$\text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}$

$\begin{array}{c}NumberofvalenceelectronsonO=6\\ Numberofnon-bondingelectrons=2\\ Numberofbondingelectrons=6\end{array}$

$\begin{array}{l}\therefore \text{Formal}\text{Charge}\text{=}{\text{N}}_{\text{valence}}\text{-}{\text{N}}_{\text{non-bond}}\text{-}\frac{{\text{N}}_{\text{bond}}}{\text{2}}\\ \text{=}6\text{-}2\text{-}\frac{6}{\text{2}}\\ \text{=}+1\end{array}$

Thus from the formal charge given above, the Structure B is most reasonable