Chapter 1, Problem 1.7P

Draw a Lewis structure for each ion.

a. ${\text{CH}}_3{\text{O}}^{-}$ b. ${\text{HC}}_{\text{2}}^{-}$ c. ${\left({\text{CH}}_{\text{3}}{\text{NH}}_{\text{3}}\right)}^{+}$ d. ${\left({\text{CH}}_{\text{3}}\text{NH}\right)}^{-}$

Interpretation Introduction

(a)

Interpretation: The Lewis structure for ${\text{CH}}_{\text{3}}{\text{O}}^{-}$ is to be drawn.

Concept Introduction: Lewis structures are electron dot representations for molecules. These structures show the bonding between the atoms or molecules and the lone pairs of electrons. The arrangement of valence electrons among the atoms in a molecule is represented by its Lewis structure.

Answer to Problem 1.7P

The Lewis structure for ${\text{CH}}_{\text{3}}{\text{O}}^{-}$ is shown in Figure 2.

Explanation of Solution

In the given molecular formula, ${\text{CH}}_{\text{3}}{\text{O}}^{-}$, the atoms are arranged as,

Figure 1

The total valence electrons in ${\text{CH}}_{\text{3}}{\text{O}}^{-}$ are,

$\begin{array}{l}\left(\text{1C}\times {\text{4e}}^{-}\right)+\left(\text{3H}\times {\text{1e}}^{-}\right)+\left(\text{1O}\times 6{\text{e}}^{-}\right)+1{\text{e}}^{-}(\text{negative}\text{charge})\\ =4{\text{e}}^{-}+3{\text{e}}^{-}+6{\text{e}}^{-}+1{\text{e}}^{-}\\ =14{\text{e}}^{-}\end{array}$

The bonds and lone pairs are added to form $\text{C}-\text{C, C}-\text{H, C}-\text{O}$ bonds. The Lewis structure for ${\text{CH}}_{\text{3}}{\text{O}}^{-}$ is shown below.

Figure 2

Conclusion

The Lewis structure for ${\text{CH}}_{\text{3}}{\text{O}}^{-}$ is shown in Figure 2.

Interpretation Introduction

(b)

Interpretation: The Lewis structure for ${\text{HC}}_{\text{2}}^{-}$ is to be drawn.

Concept Introduction: Lewis structures are electron dot representations for molecules. These structures show the bonding between the atoms or molecules and the lone pairs of electrons. The arrangement of valence electrons among the atoms in a molecule is represented by its Lewis structure.

Answer to Problem 1.7P

The Lewis structure of ${\text{HC}}_{\text{2}}^{-}$ is shown in Figure 5.

Explanation of Solution

In the given molecular formula, ${\text{HC}}_{\text{2}}^{-}$, the atoms are arranged as,

Figure 3

The total valence electrons in ${\text{HC}}_{\text{2}}^{-}$ are,

$\begin{array}{l}\left(\text{2C}\times {\text{4e}}^{-}\right)+\left(\text{1H}\times {\text{1e}}^{-}\right)+1{\text{e}}^{-}(\text{negative}\text{charge})\\ =8{\text{e}}^{-}+1{\text{e}}^{-}+1{\text{e}}^{-}\\ =10{\text{e}}^{-}\end{array}$

The bonds and lone pairs are added to form $\text{C}-\text{C}$ and $\text{C}-\text{H}$ bonds but one $\text{C}$ has incomplete octet. Lone pairs is converted into bond pairs which forms triple bond as given below

Figure 4

The Lewis structure for ${\text{HC}}_{\text{2}}^{-}$ is shown below.

Figure 5

Conclusion

The Lewis structure of ${\text{HC}}_{\text{2}}^{-}$ is shown in Figure 5.

Interpretation Introduction

(c)

Interpretation: The Lewis structure for ${{\text{(CH}}_{\text{3}}{\text{NH}}_{\text{3}}\text{)}}^{\text{+}}$ is to be drawn.

Concept Introduction: Lewis structures are electron dot representations for molecules. These structures show the bonding between the atoms or molecules and the lone pairs of electrons. The arrangement of valence electrons among the atoms in a molecule is represented by its Lewis structure.

Answer to Problem 1.7P

The Lewis structure of ${{\text{(CH}}_{\text{3}}{\text{NH}}_{\text{3}}\text{)}}^{\text{+}}$ is shown Figure 7.

Explanation of Solution

In the given molecular formula, ${{\text{(CH}}_{\text{3}}{\text{NH}}_{\text{3}}\text{)}}^{\text{+}}$, the atoms are arranged as,

Figure 6

The total valence electrons in ${{\text{(CH}}_{\text{3}}{\text{NH}}_{\text{3}}\text{)}}^{\text{+}}$ are,

$\begin{array}{l}\left(\text{1C}\times {\text{4e}}^{-}\right)+\left(\text{6H}\times {\text{1e}}^{-}\right)+\left(\text{1N}\times 5{\text{e}}^{-}\right)-1{\text{e}}^{-}(\text{positive}\text{charge})\\ =4{\text{e}}^{-}+6{\text{e}}^{-}+5{\text{e}}^{-}-1{\text{e}}^{-}\\ =14{\text{e}}^{-}\end{array}$

The bonds and lone pairs are added to form $\text{C}-\text{N, C}-\text{H, N}-\text{H}$ bonds. The Lewis structure for ${{\text{(CH}}_{\text{3}}{\text{NH}}_{\text{3}}\text{)}}^{\text{+}}$ is shown below.

Figure 7

Conclusion

The Lewis structure of ${{\text{(CH}}_{\text{3}}{\text{NH}}_{\text{3}}\text{)}}^{\text{+}}$ is shown Figure 7.

Interpretation Introduction

(d)

Interpretation: The Lewis structure for ${{\text{(CH}}_{\text{3}}\text{NH)}}^{-}$ is to be drawn.

Concept Introduction: Lewis structures are electron dot representations for molecules. These structures show the bonding between the atoms or molecules and the lone pairs of electrons. These structures can be drawn for any covalently bonded molecules.

Answer to Problem 1.7P

The Lewis structure of ${{\text{(CH}}_{\text{3}}\text{NH)}}^{-}$ is shown in Figure 9.

Explanation of Solution

The given molecular formula, ${{\text{(CH}}_{\text{3}}\text{NH)}}^{-}$ in which atoms are arranged as,

Figure 8

The total valence electrons in ${{\text{(CH}}_{\text{3}}\text{NH)}}^{-}$ are,

$\begin{array}{l}\left(\text{1C}\times {\text{4e}}^{-}\right)+\left(\text{4H}\times {\text{1e}}^{-}\right)+\left(\text{1N}\times 5{\text{e}}^{-}\right)+1{\text{e}}^{-}(\text{negative}\text{charge})\\ =4{\text{e}}^{-}+4{\text{e}}^{-}+5{\text{e}}^{-}+1{\text{e}}^{-}\\ =14{\text{e}}^{-}\end{array}$

The bonds and lone pairs are added to form $\text{C-N, C-H, N-H}$ bonds. The Lewis structure for ${{\text{(CH}}_{\text{3}}\text{NH)}}^{-}$ is shown below.

Figure 9

Conclusion

The Lewis structure of ${{\text{(CH}}_{\text{3}}\text{NH)}}^{-}$ is shown in Figure 9.