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Chapter 6: Problem 71

Draw a combined Lewis dot, molecular-shape diagram for each of the following species. Name each shape, and indicate whether the molecule or ion has a dipole moment. If so, draw the dipole moment vector. (Hint: See problem statement and hint for Problem 6.69.) (a) \(\mathrm{CHBr}_{3}\) (b) \(\mathrm{NF}_{3}\) (c) \(\mathrm{ClO}_{3}^{-}\) (d) \(\mathrm{CS}_{2}\)

Short Answer

Expert verified
(a) \(\mathrm{CHBr}_{3}\): Tetrahedral molecular shape. It has a net dipole moment, with the dipole moment vector pointing towards the Bromine atoms. (b) \(\mathrm{NF}_{3}\): Trigonal pyramidal molecular shape. It has a net dipole moment, with the dipole moment vector pointing towards the Fluorine atoms. (c) \(\mathrm{ClO}_{3}^{-}\): Trigonal pyramidal molecular shape. It has a net dipole moment, with the dipole moment vector pointing towards the Oxygen atoms. (d) \(\mathrm{CS}_{2}\): Linear molecular shape. It has no net dipole moment as the bond dipoles cancel each other out.

Step by step solution

01

Draw the Lewis dot structure

Carbon has 4 valence electrons, and each Bromine has 7 valence electrons. The resulting Lewis dot structure will have Carbon in the center, bonded to each of the 3 Bromine atoms with single bonds. There will be 3 lone pairs on each Bromine atom.
02

Determine electron-domain geometry and molecular shape

The central atom, Carbon, has four electron domains (three single bonds and one lone pair). According to the VSEPR theory, this gives us a tetrahedral electron-domain geometry. Since all the electron domains are involved in bonding, the molecular shape is also tetrahedral.
03

Dipole moment and dipole moment vector

The \(\mathrm{C-H}\) bond is nonpolar, while the C-Br bonds are polar due to the difference in electronegativity between Carbon and Bromine atoms. Since the molecular shape is tetrahedral, the three C-Br bond dipoles will not cancel out, resulting in a net dipole moment for the molecule. The dipole moment vector is pointing towards the negative end, which is pointing towards the three Bromine atoms. (b) \(\mathrm{NF}_{3}\)
04

Draw the Lewis dot structure

Nitrogen has 5 valence electrons, and each Fluorine atom has 7 valence electrons. The Lewis dot structure has Nitrogen in the center, bonded to each of the 3 Fluorine atoms with single bonds. There will be 3 lone pairs on each Fluorine atom, and one lone pair on Nitrogen.
05

Determine electron-domain geometry and molecular shape

The central atom, Nitrogen, has four electron domains (three single bonds and one lone pair). According to the VSEPR theory, this gives us a tetrahedral electron-domain geometry. Since one of the electron domains is a lone pair, the molecular shape is trigonal pyramidal.
06

Dipole moment and dipole moment vector

The N-F bonds are polar due to the difference in electronegativity between Nitrogen and Fluorine atoms. The molecular shape is trigonal pyramidal, so the bond dipoles will not cancel each other out, resulting in a net dipole moment for the molecule. The dipole moment vector is pointing towards the negative end, which is pointing towards the three Fluorine atoms. (c) \(\mathrm{ClO}_{3}^{-}\)
07

Draw the Lewis dot structure

Chlorine has 7 valence electrons, and each Oxygen atom has 6 valence electrons. In addition, there is 1 extra electron due to negative charge. The Lewis dot structure has Chlorine in the center, bonded to each of the 3 Oxygen atoms with single bonds. There will be 3 lone pairs on each Oxygen atom and 3 lone pairs on Chlorine.
08

Determine electron-domain geometry and molecular shape

The central atom, Chlorine, has four electron domains (three single bonds and one lone pair). According to the VSEPR theory, this gives us a tetrahedral electron-domain geometry. Since one of the electron domains is a lone pair, the molecular shape is trigonal pyramidal.
09

Dipole moment and dipole moment vector

The Cl-O bonds are polar due to the difference in electronegativity between Chlorine and Oxygen atoms. The molecular shape is trigonal pyramidal, so the bond dipoles will not cancel each other out, resulting in a net dipole moment for the ion. The dipole moment vector is pointing towards the negative end, which is pointing towards the three Oxygen atoms. (d) \(\mathrm{CS}_{2}\)
10

Draw the Lewis dot structure

Carbon has 4 valence electrons, and each Sulfur atom has 6 valence electrons. The Lewis dot structure has Carbon in the center, double bonded to each of the 2 Sulfur atoms. There will be 2 lone pairs on each Sulfur atom.
11

Determine electron-domain geometry and molecular shape

The central atom, Carbon, has two electron domains (two double bonds). According to the VSEPR theory, this gives us a linear electron-domain geometry. Since all the electron domains are involved in bonding, the molecular shape is also linear.
12

Dipole moment and dipole moment vector

The C-S bonds are polar due to the difference in electronegativity between Carbon and Sulfur atoms. However, the molecular shape is linear, so the bond dipoles will cancel each other out, resulting in no net dipole moment for the molecule. There is no dipole moment vector for this molecule.

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Most popular questions from this chapter

Consider the \(\mathrm{CH}_{3}\) anion. (a) Draw and name its three-dimensional shape and indicate the predicted values of its bond angles. (b) Explain how the structure of this anion would compare with that of \(\mathrm{NH}_{3}\) and why both would have bond angles that are less than ideal.

$$ \mathrm{C}_{2} \mathrm{Cl}_{2} \text { , which is connected } \mathrm{Cl}-\mathrm{C}-\mathrm{C}-\mathrm{Cl} . $$

Is chloroform, \(\mathrm{CHCl}_{3}\), a polar molecule? If it is, draw the dipole moment vector for the entire molecule and show where the \(\delta+\) and \(\delta-\) regions of the molecule are.

Consider the molecule \(\mathrm{SiCl}_{4}\). (a) Draw the dot diagram. (b) Draw the molecule's three-dimensional shape, and label the numeric value of all bond angles. (c) What is the shape of this molecule? (d) Draw in the individual bond dipole moments. (e) Is the molecule polar? If yes, draw the molecular dipole moment vector.

Consider \(\mathrm{SO}_{2}\) and \(\mathrm{CO}_{2}\). Both have polar covalent bonds. One of these molecules is polar and the other is nonpolar. Which is which and why?
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