Chapter 13, Problem 28E

Interpretation Introduction

(a)

Interpretation:

The electron-pair geometry for each carbon and nitrogen atoms in the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is to be explained and the Lewis diagram for the molecule is to be drawn.

Concept introduction:

The electron pairs in Lewis diagrams repel each other in real molecule and thus they distribute themselves in positions around the central atoms which are far away from one another. This arrangement of electron pairs is called electron-pair geometry. The electron pairs may be shared in covalent bond, or they may be lone pairs.

Answer to Problem 28E

The Lewis diagram for the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is shown below.

The electron pair geometry for the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ is tetrahedral, for the carbon $\left(\text{C}=\text{O}\right)$ is trigonal planar and for the nitrogen atom is tetrahedral.

Explanation of Solution

To write the Lewis diagram for a compound first the number of valence electrons is to be calculated. In the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$, each carbon has four valence electrons, each hydrogen has one valence electron, oxygen has six valence electrons, and nitrogen has five valence electrons. The total number of valence electron for the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is calculated below.

$\begin{array}{rll}\text{Total}\text{number}\text{of}\text{valence}\text{electron}& =& \left(2\times 4+5\times 1+6+5\right)e^{-}\\ & =& 24e^{-}\end{array}$

In the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$, carbon atom is bonded with hydrogen, oxygen, and nitrogen atoms. In Lewis diagram, each electron is placed around the atom such that the octet rule is obeyed. Therefore, the Lewis diagram of ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is shown below.

Figure 1

The electron-pair geometry depends on the number of electron pairs around the central atoms. In the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$, there are four electron-pairs around the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ and nitrogen atoms, and there are three electron-pairs around the carbon $\left(\text{C}=\text{O}\right)$. Therefore, the electron pair geometry for the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ is tetrahedral, for the carbon $\left(\text{C}=\text{O}\right)$ is trigonal planar and for the nitrogen atom is tetrahedral.

Conclusion

The Lewis diagram for the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is shown in the Figure 1. The electron pair geometry for the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ is tetrahedral, for the carbon $\left(\text{C}=\text{O}\right)$ is trigonal planar and for the nitrogen atom is tetrahedral.

Interpretation Introduction

(b)

Interpretation:

The molecular geometry predicted by the valence shell electron-pair repulsion theory for each carbon and nitrogen atoms in the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is to be explained and the Lewis diagram for the molecule is to be drawn.

Concept introduction:

Molecular geometry is the precise term that is used to describe the shape of molecules and arrangement of atoms around the central atom. The molecular geometry of a molecule is predicted by valence shell electron-pair repulsion theory or in short VSEPR theory. VSEPR theory applies to substances in which a second period element is bonded to two, three, four, or other atoms.

Answer to Problem 28E

The Lewis diagram for the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is shown below.

The molecular geometry for the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ is tetrahedral, for the carbon $\left(\text{C}=\text{O}\right)$ is trigonal planar and for the nitrogen atom is trigonal pyramidal.

Explanation of Solution

To write the Lewis diagram for a compound first the number of valence electrons is to be calculated. In the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$, each carbon has four valence electrons, each hydrogen has one valence electron, oxygen has six valence electrons, and nitrogen has five valence electrons. The total number of valence electron for the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is calculated below.

$\begin{array}{rll}\text{Total}\text{number}\text{of}\text{valence}\text{electron}& =& \left(2\times 4+5\times 1+6+5\right)e^{-}\\ & =& 24e^{-}\end{array}$

In the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ carbon atom is bonded with hydrogen, oxygen, and nitrogen atoms. In Lewis diagram each electron is placed around the atom such that the octet rule is obeyed. Therefore, the Lewis diagram of ${\text{CH}}_3{\text{CONH}}_{\text{2}}$ is shown below.

Figure 1

The molecular geometry depends on the number of electron pairs as well as number of lone-pair electrons on the central atoms. In the molecule ${\text{CH}}_3{\text{CONH}}_{\text{2}}$, there are four electron-pairs around the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ and nitrogen atoms, and there are three electron-pairs around the carbon $\left(\text{C}=\text{O}\right)$. Due to the presence of lone-pair of electrons on the nitrogen atom the geometry becomes distort and changes to the trigonal pyramidal. Therefore, the molecular geometry for the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ is tetrahedral, for the carbon $\left(\text{C}=\text{O}\right)$ is trigonal planar and for the nitrogen atom is trigonal pyramidal.

Conclusion

The Lewis diagram for the molecule ${\text{CH}}_{\text{3}}{\text{CH}}_2\text{COOH}$ is shown in the Figure 1. The molecular geometry for the carbon $\left(-{\text{CH}}_{\text{3}}\right)$ is tetrahedral, for the carbon $\left(\text{C}=\text{O}\right)$ is trigonal planar and for the nitrogen atom is trigonal pyramidal.