Chapter 9, Problem 9.82QE

(a)

Interpretation Introduction

Interpretation:

The resonance structures with an octet about the central atom and a resonance structure that has minimum formal charges for the following structure has to be determined.

Concept Introduction:

A covalent bond is a bond that is formed from the mutual sharing of electrons between atoms. Lewis structures are representations of the covalent bond. In this, Lewis symbols show how the valence electrons are present in the molecule.

Steps to write Lewis structures are as follows:

1. The skeleton structure with single bonds between all bonded atoms has to be written

2. Sum the valence electrons of the atoms in the molecule.

(a) For cations, one electron is subtracted for each positive charge.

(b) For anions, one electron is added for each negative charge.

3. Subtract two electrons from total number of valence electrons for each bond in the skeleton structure.

4. Count the number of electrons required to satisfy the octet rule for each atom in the structure. If the number of electrons needed is less than the number remaining, add one bond for every two electrons needed between atoms to attain an octet.

5. The remaining electrons are placed as lone pairs on atoms that need them to satisfy the octet rule.

The formula to calculate formal charge of atom is,

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

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

Resonance structure comprises of two or more Lewis Structures that describes the arrangement of bond of a single species and include fractional bonds and fractional charges.

Answer to Problem 9.82QE

The resonance structure that has an octet around central atom is as follows:

The resonance structure that minimizes formal charge is as follows:

Explanation of Solution

The skeleton structure is as follows:

The resonance structures are as follows:

For structure I:

Substitute 6 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 $\text{S}$ atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{S}\right)=\left(6\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+2\end{array}$

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 II:

Substitute 6 for valence electrons, 0 for the number of lone pairs of electrons and 12 for the number of shared electrons in equation (1) to calculate the formal charge on $\text{S}$ atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{S}\right)=\left(6\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(12\right)\right)\\ =0\end{array}$

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, 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, 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.

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

Possible resonance structures are as follows:

Hence, structure I has an octet around central atom and structure II minimizes the formal charge.

(b)

Interpretation Introduction

Interpretation:

The resonance structures with an octet about the central atom and a resonance structure that has minimum formal charges for the following structure has to be determined.

Concept introduction:

Refer to part (a)

Answer to Problem 9.82QE

The resonance structure that has an octet around central atom is as follows:

The resonance structure that minimizes formal charge is as follows:

Explanation of Solution

The skeleton structure is as follows:

The possible resonance structures are as follows:

For structure I:

Substitute 7 for valence electrons, 4 for the number of lone pairs of electrons and 4 for the number of shared electrons in equation (1) to calculate the formal charge on $\text{Cl}$ atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{Cl}\right)=\left(7\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(8\right)\right)\\ =+3\end{array}$

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.

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

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, 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.

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

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 fourth oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_4\right)=\left(6\right)-\left(\left(6\right)+\left(\frac{1}{2}\right)\left(2\right)\right)\\ =-1\end{array}$

For structure II:

Substitute 7 for valence electrons, 0 for the number of lone pairs of electrons and 8 for the number of shared electrons in equation (1) to calculate the formal charge on $\text{Cl}$ atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left(\text{Cl}\right)=\left(7\right)-\left(\left(0\right)+\left(\frac{1}{2}\right)\left(14\right)\right)\\ =0\end{array}$

Substitute 6 for valence electrons, 4 for number of lone pairs of electrons and 4for 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, 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.

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

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 fourth oxygen atom.

  $\begin{array}{c}\text{Formal}\text{charge}\left({\text{O}}_4\right)=\left(6\right)-\left(\left(4\right)+\left(\frac{1}{2}\right)\left(4\right)\right)\\ =0\end{array}$

Possible resonance structures are as follows:

Hence, structure I has an octet around central atom and structure II minimizes the formal charge.