Chapter 10, Problem 10.34QE

(a)

Interpretation Introduction

Interpretation:

Lewis structure for ${\text{ClC(O)NH}}_{\text{2}}$ has to be written and also the skeleton structure has to be deduced from the formula.

Concept Introduction:

Lewis structure is used for predicting the shape of molecules.  From the steric number obtained in a Lewis structure, the molecular geometry can be predicted.  VSEPR model can predict the shape of molecules considering their Lewis structure.  Certain rules has to be followed in for the VSEPR model.

• The molecule will have a shape where there is minimal electrostatic repulsion between the valence‑shell electron pairs.
• The forces of repulsion between two lone pairs of electrons will be higher than the repulsion between lone pair and bond pair of electrons.  This in turn will be higher than the bond pair‑bond pair of electrons.

Explanation of Solution

Lewis structure for ${\text{ClC(O)NH}}_{\text{2}}$:

The total number of valence electrons present in ${\text{ClC(O)NH}}_{\text{2}}$ is calculated as follows;

    $\begin{array}{c}\text{Total}\text{number}\text{of}\text{valence}\text{electrons}=(1\times 7)+(1\times 4)+(1\times 6)+(1\times 5)+(2\times 1)\\ =7+4+6+5+2\\ =24\end{array}$

The skeletal structure can be drawn considering the formula as shown below;

Ten electrons are used up in the skeletal structure.  Among the remaining fourteen valence-electrons, six are placed over chlorine atom and six are placed over oxygen atom.  Two electrons are placed over nitrogen atom.

Thus the Lewis structure of ${\text{ClC(O)NH}}_{\text{2}}$ is drawn as shown;

Bond Angles:

There is a carbon atom and a nitrogen atom as central atom in the Lewis structure.  The steric number of the central atom can be used to predict the bond angles of the central atoms.

Steric number for carbon atom:

The number of lone pair of electrons on carbon atom is zero while the number of atoms that are bonded to carbon is three.  Therefore, steric number can be calculated as shown below;

    $\begin{array}{c}\text{Steric}\text{number}=0+3\\ =3\end{array}$

As the steric number is three, and only bonding pair of electrons are present, the arrangement is trigonal planar and the bond angle will be $\text{120}\text{°}$.

Steric number for nitorgen atom:

The number of lone pair of electrons on nitrogen atom is one while the number of atoms that are bonded to nitrogen is three.  Therefore, steric number can be calculated as shown below;

    $\begin{array}{c}\text{Steric}\text{number}=1+3\\ =4\end{array}$

As the steric number is four, the arrangement is tetrahedral and the bond angle will be $\text{109}\text{.5}\text{°}$.

(b)

Interpretation Introduction

Interpretation:

Lewis structure for ${\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ has to be written and also the skeleton structure has to be deduced from the formula.

Concept Introduction:

Refer part (a).

Explanation of Solution

Lewis structure for ${\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$:

The total number of valence electrons present in ${\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ is calculated as follows;

    $\begin{array}{c}\text{Total}\text{number}\text{of}\text{valence}\text{electrons}=(6\times 1)+(2\times 6)+(2\times 4)\\ =6+12+8\\ =26\end{array}$

The skeletal structure can be drawn considering the formula as shown below;

Eighteen electrons are used up in the skeletal structure.  Among the remaining eight valence-electrons, four are placed over oxygen atom each.  Thus the Lewis structure for ${\text{HOCH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{OH}$ is drawn as shown;

Bond Angles:

There are two carbon atoms as central atoms in the Lewis structure.  The steric number of the central atom can be used to predict the bond angles of the central atoms.

Steric number for carbon atom:

The number of lone pair of electrons on carbon atom is zero while the number of atoms that are bonded to carbon is four.  Therefore, steric number can be calculated as shown below;

    $\begin{array}{c}\text{Steric}\text{number}=0+4\\ =4\end{array}$

As the steric number is four, the arrangement is tetrahedral and the bond angle will be $\text{109}\text{.5}\text{°}$.

(c)

Interpretation Introduction

Interpretation:

Lewis structure for $\text{NCCN}$ has to be written and also the skeleton structure has to be deduced from the formula.

Concept Introduction:

Refer part (a).

Explanation of Solution

Lewis structure for $\text{NCCN}$:

The total number of valence electrons present in $\text{NCCN}$ is calculated as follows;

    $\begin{array}{c}\text{Total}\text{number}\text{of}\text{valence}\text{electrons}=(2\times 5)+(2\times 4)\\ =10+8\\ =18\end{array}$

The skeletal structure can be drawn considering the formula as shown below;

Six electrons are used up in the skeletal structure.  Among the remaining twelve valence-electrons, six are placed over nitrogen atom each.  Thus the Lewis structure for $\text{NCCN}$ is drawn as shown;

Bond Angles:

There are two carbon atoms as central atoms in the Lewis structure.  The steric number of the central atom can be used to predict the bond angles of the central atoms.

Steric number for carbon atom:

The number of lone pair of electrons on carbon atom is zero while the number of atoms that are bonded to carbon is two.  Therefore, steric number can be calculated as shown below;

    $\begin{array}{c}\text{Steric}\text{number}=0+2\\ =2\end{array}$

As the steric number is two, the arrangement is linear and the bond angle will be $\text{180}\text{°}$.