Chapter 4, Problem 26E

Two variations of the octahedral geometry (see Table 4-1) are illustrated below.

Which of the compounds/ions Br₃⁻, ClF₃, XeF₄, SF₄, PF₅, ClF₅, and SF₆ have these molecular structures?

Interpretation Introduction

Interpretation: Interpretation: The molecular structure of given compound is to be predicted from given structures.

Concept introduction: Molecular structure is a three-dimensional shape of a molecule.

Bond angle is the angle between atoms of molecule.

To determine: The correct molecular structure of ${\text{Br}}_3{}^{-},{\text{ClF}}_3,{\text{XeF}}_4,{\text{SF}}_4,{\text{PF}}_5,{\text{ClF}}_5$ and ${\text{SF}}_4$(including bond angles) according to given structure.

Explanation of Solution

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The atomic number of bromine $\left(\text{Br}\right)$ is 35 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^{\text{6}}{\text{3d}}^{\text{10}}{\text{4s}}^{\text{2}}{\text{4p}}^{\text{5}}$

The valence electron of bromine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{3Br}\text{+}1e\text{=}\text{7}\times \text{3}\text{+}1\\ \text{=}2\text{2}\end{array}$

The Lewis structure of ${\text{Br}}_3{}^{-}$ is

Figure 1

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{7+1}{2}\\ =4\end{array}$

Refer to table (4-1)

The shape of compound is linear and bond angle is ${180}^0$

Explanation:

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The atomic number of (central atom) chlorine $\left(\text{Cl}\right)$ is 17 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^5$

The valence electron of chlorine is 7

The atomic number of fluorine $\left(\text{F}\right)$ is 9 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

The valence electron of fluorine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{3Cl}\text{+}\text{F}\text{=}\text{7}\times \text{3}\text{+}7\\ \text{=}28\end{array}$

The Lewis structure of ${\text{ClF}}_3$ is

’

Figure 2

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{7+3}{2}\\ =5\end{array}$

Refer to table (4-1)

The shape of compound is T-shape.

Explanation:

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The atomic number of central atom sulfur $\left(\text{S}\right)$ is 16 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^4$

The valence electron of sulfur is 6

The atomic number of fluorine $\left(\text{F}\right)$ is 9 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

The valence electron of fluorine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{S}\text{+}4\text{F}\text{=}6\text{+}4\times 7\\ \text{=}34\end{array}$

The Lewis structure of ${\text{SF}}_4$ is

Figure 3

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{6+4}{2}\\ =5\end{array}$

Refer to table (4-1)

The shape of compound is see-saw-shape.

Explanation:

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The central atom in ${\text{XeF}}_4$ is xenon $\left(\text{Xe}\right)$. The atomic number of xenon is 54 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^{\text{6}}{\text{3d}}^{\text{10}}{\text{4s}}^{\text{2}}{\text{4p}}^{\text{6}}{\text{4d}}^{\text{10}}{\text{5s}}^{\text{2}}{\text{5p}}^{\text{6}}$

The valence electron of xenon is 8

The atomic number of fluorine $\left(\text{F}\right)$ is 9 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

The valence electron of fluorine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{Xe}\text{+}4\text{F}\text{=}8\text{+}4\times 7\\ \text{=}36\end{array}$

The Lewis structure of ${\text{XeF}}_4$ is

Figure 4

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{8+4}{2}\\ =6\end{array}$

Refer to table (4-1)

Explanation:

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The central atom in ${\text{PF}}_5$ is phosphorous $\left(\text{P}\right)$. The electronic configuration of phosphorous is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^3$

The valence electron of phosphorous is 5

The atomic number of fluorine $\left(\text{F}\right)$ is 9 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

The valence electron of fluorine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{P}\text{+}5\text{F}\text{=}5\text{+}5\times 7\\ \text{=}40\end{array}$

The Lewis structure of ${\text{PF}}_5$ is

Figure 5

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{5+5}{2}\\ =5\end{array}$

Refer to table (4-1)

The shape of compound is trigonal bipyramidal shape.

Explanation:

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The atomic number of (central atom) chlorine $\left(\text{Cl}\right)$ is 17 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^5$

The valence electron of chlorine is 7

The atomic number of fluorine $\left(\text{F}\right)$ is 9 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

The valence electron of fluorine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{Cl}\text{+}5\text{F}\text{=}7\text{+}5\times 7\\ \text{=}42\end{array}$

The Lewis structure of ${\text{ClF}}_5$ is

Figure 6

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{7+5}{2}\\ =6\end{array}$

Refer to table (4-1)

The shape of compound is trigonal square pyramidal.

Explanation:

The steps are to be followed to determine the molecular structure is:

• Identify the central atom.
• Count its valence electrons.
• Add or subtract electrons for charge.
• Draw the Lewis structure.
• Divide the total number of electrons by 2 to find the number of electron pairs.
• Use this number to predict the shape.

The atomic number of central atom sulfur $\left(\text{S}\right)$ is 16 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^{\text{6}}{\text{3s}}^{\text{2}}{\text{3p}}^4$

The valence electron of sulfur is 6

The atomic number of fluorine $\left(\text{F}\right)$ is 9 and its electronic configuration is,

${\text{1s}}^{\text{2}}{\text{2s}}^{\text{2}}{\text{2p}}^5$

The valence electron of fluorine is 7

The total number of valence electrons is,

$\begin{array}{c}\text{S}\text{+}6\text{F}\text{=}6\text{+}6\times 7\\ \text{=}48\end{array}$

The Lewis structure of ${\text{SF}}_6$ is

Figure 7

The formula of number of electron pairs is

$X=\frac{V+M\pm C}{2}$

Where,

• $X$ is number of electron pairs
• $V$ is valence electrons of central atom
• $M$ is number of monovalent atoms
• $C$ is charge on compound

The number of electron pairs is

$\begin{array}{c}X=\frac{V+M\pm C}{2}\\ X=\frac{6+6}{2}\\ =6\end{array}$

Refer to table (4-1)

The shape of compound is octahedral.

Conclusion

The molecular structure describes the relative position of atoms in a molecule. The shape of ${\text{ClF}}_5$ and ${\text{XeF}}_{\text{4}}$ are square planner and square pyramidal shape.