Chapter 9, Problem 9.74QE

(a)

Interpretation Introduction

Interpretation:

The possible resonance structures for the following skeleton structure have to be determined. Also, the most important resonance structure has to be identified.

Concept Introduction:

The steps to draw the Lewis structure of the molecule are as follows:

Step 1: Find the central atom and place the other atoms around it. The atom in a compound that has the lowest group number or lowest electronegativity considered as the central atom.

Step 2: Estimate the total number of valence electrons.

Step 3: Connect the other atoms around the central atoms to the central atom with a single bond and lower the value of valence electrons by 2 of every single bond.

Step 4: Allocate the remaining electrons in pairs so that each atom can get 8 electrons.

The formula to calculate formal charge of the atom is as follows:

  $\text{Formal}\text{charge}=\left(\begin{array}{l}\text{number}\text{of}\\ \text{valence}\\ \text{electrons}\end{array}\right)-\left(\left(\begin{array}{l}\text{number}\text{of}\\ \text{lone pairs of}\\ \text{electrons}\end{array}\right)+\left(\frac{1}{2}\right)\left(\begin{array}{l}\text{number}\text{of}\\ \text{shared}\\ \text{electrons}\end{array}\right)\right)$        (1)

Some molecules and ions do not have one unique Lewis structure. The Lewis structures that differ only in the placement of multiple bonds are called resonance structures.

Resonance structures are defined as a set of two or more Lewis structures that collectively describe the electronic bonding. The actual bonding is an average of the bonding in the resonance structures. Also, not all resonance structures contribute equally in every case. Resonance structures that have high formal charges or that place charges of the same sign on adjacent atoms do not contribute to the bonding.

Answer to Problem 9.74QE

The possible resonance structures are as follows:

All resonance structures are equally important.

Explanation of Solution

The skeleton structure is as follows:

The resonance structures are as follows:

For structure I:

Substitute 5 for valence electrons, 0 for the number of lone pair of electrons and 8 for the number of shared electrons in equation (1) to calculate the formal charge on nitrogen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{N}\right)=\left(5\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+1\end{array}$

Substitute 6 for valence electrons, 4 for the number of lone pair of electrons and 4 for the number of shared electrons in equation (1) to calculate the formal charge on first oxygen atom connected to nitrogen

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_1\right)=\left(6\right)-\left(\left(4\right)+\left(\frac{1}{2}\right)\left(4\right)\right)\\ =0\end{array}$

Substitute 6 for valence electrons, 6 for the number of lone pair of electrons and 2for the number of shared electrons in equation (1) to calculate the formal charge on second oxygen atom connected to nitrogen

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_2\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

For structure II:

Substitute 5 for valence electrons, 0 for the number of lone pair of electrons and 8 for the number of shared electrons in equation (1) to calculate the formal charge on nitrogen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{N}\right)=\left(5\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+1\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pair of electrons and 2for the number of shared electrons in equation (1) to calculate the formal charge on first oxygen atom connected to nitrogen

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_1\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

Substitute 6 for valence electrons, 4 for number of lone pair of electrons and 4 for the number of shared electrons in equation (1) to calculate the formal charge on second oxygen atom connected to nitrogen

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_2\right)=\left(6\right)-\left(\left(4\right)+\left(\frac{1}{2}\right)\left(4\right)\right)\\ =0\end{array}$

Possible resonance structures are as follows:

All the structures have same formal charge. Also, the atoms that have charge are same in each structure. Therefore, all structures are equally important.

(b)

Interpretation Introduction

Interpretation:

The possible resonance structures for the following skeleton structure have to be determined. Also, the most important resonance structure has to be identified.

Concept Introduction:

Refer to part (a).

Answer to Problem 9.74QE

The possible resonance structures are as follows:

All the structures are equally important.

Explanation of Solution

The skeleton structure is,

The resonance structures are as follows:

For structure I:

Substitute 5 for valence electrons, 0 for number of lone pairs of electrons and 8 for the number of shared electrons in equation (1) to calculate the formal charge on nitrogen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{N}\right)=\left(5\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+1\end{array}$

Substitute 6 for valence electrons, 4 for number of lone pairs of electrons and 4 for the number of shared electrons in equation (1) to calculate the formal charge on first oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_1\right)=\left(6\right)-\left(\left(4\right)+\left(\frac{1}{2}\right)\left(4\right)\right)\\ =0\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pairs of electrons and 2 for the number of shared electrons in equation (1) to calculate the formal charge on second oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_2\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pairs of electrons and 2 for the number of shared electrons in equation (1) to calculate the formal charge on third oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_3\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

For structure II:

Substitute 5 for valence electrons, 0 for number of lone pairs of electrons and 8 for the number of shared electrons in equation (1) to calculate the formal charge on nitrogen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{N}\right)=\left(5\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+1\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pairs of electrons and 2 for the number of shared electrons in equation (1) to calculate the formal charge on first oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_1\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

Substitute 6 for valence electrons, 4 for number of lone pairs of electrons and 4 for the number of shared electrons in equation (1) to calculate the formal charge on second oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_2\right)=\left(6\right)-\left(\left(4\right)+\left(\frac{1}{2}\right)\left(4\right)\right)\\ =0\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pairs of electrons and 2 for the number of shared electrons in equation (1) to calculate the formal charge on third oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_3\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

For structure III:

Substitute 5 for valence electrons, 0 for number of lone pairs of electrons and 8 for the number of shared electrons in equation (1) to calculate the formal charge on nitrogen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{N}\right)=\left(5\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+1\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pairs of electrons and 2 for the number of shared electrons in equation (1) to calculate the formal charge on first oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_1\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

Substitute 6 for valence electrons, 6 for number of lone pairs of electrons and 2 for the number of shared electrons in equation (1) to calculate the formal charge on second oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_2\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

Substitute 6 for valence electrons, 4 for number of lone pairs of electrons and 4 for the number of shared electrons in equation (1) to calculate the formal charge on third oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_3\right)=\left(6\right)-\left(\left(4\right)+\left(\frac{1}{2}\right)\left(4\right)\right)\\ =0\end{array}$

The possible resonance structures are as follows:

All the structures have the same formal charge. Also, the atoms that have charge are same in each structure. Therefore, all structures are equally important.