Chemistry The Science in Context

Thomas R. Gilbert

Chapter 9

Molecular Geometry: Shape Determines Function - all with Video Answers

Educators

Chapter Questions

Problem 1

Two compounds with the same formula, $\mathrm{S}_{2} \mathrm{F}_{2},$ have been isolated. The structures in Figure P9.1 show the arrangements of the atoms in these different compounds. Can these two compounds be distinguished by their dipole moments?

David Collins

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Problem 2

Could you distinguish between the two structures of $\mathrm{N}_{2} \mathrm{H}_{2}$ shown in Figure P9.2 by the magnitude of their dipole moments?

David Collins

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Problem 3

Which of the molecules shown in Figure P9.3 are planar; that is, all atoms are in a single plane? Are there delocalized $\pi$ electrons in any of these molecules?

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Problem 4

Which of the molecules shown in Figure P9.4 is not planar? Are there delocalized $\pi$ electrons in any of these molecules?

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Problem 5

Use the MO diagram in Figure P9.5 to predict whether $\mathrm{O}_{2}^{+}$ has more or fewer electrons in antibonding molecular orbitals than $\mathrm{O}_{2}^{2+}.$

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Problem 6

Under appropriate conditions, $I_{2}$ can be oxidized to $I_{2}^{+}$ which is bright blue. The corresponding anion, $I_{2}^{-}$, is not known. Use the molecular orbital diagram in Figure $\mathrm{P} 9.6$ to explain why $\mathrm{I}_{2}^{+}$ is more stable than $\mathrm{I}_{2}^{-}$.

David Collins

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Problem 7

The molecular geometry of $\operatorname{Re} \mathrm{F}_{7}$ is an uncommon structure called a pentagonal bipyramid, which is shown in Figure P9.7. What are the bond angles in a pentagonal bipyramid?

David Collins

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Problem 8

Use representations $[\mathrm{A}]$ through $[\mathrm{I}]$ in Figure $\mathrm{P} 9.8$ to answer questions a-f.
a. Which representations depict orbital overlap?
b. Which molecules contain $\pi$ electrons?
c. Which molecules contain delocalized $\pi$ electrons?
d. Identify all the functional groups present in each molecule that contains one or more functional groups.
e. Look at $[\mathrm{C}],[\mathrm{F}],$ and $[\mathrm{I}] .$ Which ones, if any, are polar?
f. Which molecules contain $s p^{2}$ hybridized oxygen atoms? Which contain $s p^{3}$ hybridized oxygen atoms?

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Problem 9

Why is the shape of a molecule determined by repulsions between electron pairs and not by repulsions between nuclei?

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Problem 10

Do all resonance forms of a molecule have the same molecular geometry? Explain your answer.

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Problem 11

How can $\mathrm{SO}_{3}$ and $\mathrm{BF}_{3}$ have different numbers of bonds but the same trigonal planar geometry?

David Collins

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Problem 12

Account for the range of bond angles from less than $100^{\circ}$ to $180^{\circ}$ in triatomic molecules.

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Problem 13

In a molecule of ammonia, why is the repulsion between the lone pair and a bonding pair of electrons on nitrogen greater than the repulsion between two N-H bonding pairs?

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Problem 14

Why is it important to draw a correct Lewis structure for a molecule before predicting its geometry?

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Problem 15

Why does the seesaw structure have lower energy than a trigonal pyramidal structure derived by removing an axial atom from a trigonal bipyramidal $\mathrm{AB}_{5}$ molecule?

David Collins

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Problem 16

Which geometry do you predict will have lower energy: a square pyramid or a trigonal bipyramid? Why?

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Problem 17

Arrange the following molecular geometries in order of increasing bond angle: (a) trigonal planar; (b) octahedral; (c) tetrahedral.

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Problem 18

Arrange the following molecular geometries in order of increasing bond angle: (a) square planar; (b) tetrahedral; (c) square pyramidal.

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Problem 19

Which of the molecular geometries discussed in this chapter have more than one characteristic bond angle?

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Problem 20

Which molecular geometries for molecules of the general formula $\mathrm{AB}_{x}(x=2 \text { to } 6$ ) discussed in this chapter have the same bond angles when lone pairs replace one or more atoms?

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Problem 21

Which of the following molecular geometries does not lead to linear triatomic molecules after the removal of one or more atoms? (a) tetrahedral; (b) octahedral; (c) T-shaped

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Problem 22

Which of the following molecular geometries does not lead to linear triatomic molecules after the removal of one or more atoms? (a) trigonal bipyramidal; (b) seesaw; (c) trigonal planar

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Problem 23

Describe the molecular geometries that result from replacing one atom with a lone pair of electrons in an $\mathrm{AB}_{7}$ molecule with a pentagonal bipyramidal geometry.

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Problem 24

Which atoms would you have to remove from the cubic $A B_{8}$ molecule shown in Figure P9.24 to create a geometry that approximates an octahedron?

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Problem 25

Determine the molecular geometries of the following molecules: (a) $\mathrm{GeH}_{4}$; (b) $\mathrm{PH}_{3} ;$ (c) $\mathrm{H}_{2} \mathrm{S} ;$ (d) $\mathrm{CHCl}_{3}$

David Collins

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Problem 26

Determine the molecular geometries of the following molecules and ions: (a) $\mathrm{NO}_{3}^{-} ;$ (b) $\mathrm{NO}_{4}^{3-}$ (c) $\mathrm{S}_{2} \mathrm{O} ;$ (d) $\mathrm{NF}_{3}$

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Problem 27

Determine the bond angles in the following ions:
(a) $\mathrm{NH}_{4}^{+}$
(b) $\mathrm{SO}_{3}^{2-} ;$
(c) $\mathrm{NO}_{2}^{-} ;$
(d) $\mathrm{XeF}_{5}^{+}$

David Collins

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Problem 28

Determine the bond angles in the following ions:
(a) $\mathrm{SCN}^{-}$
(b) $\mathrm{BF}_{2}^{+} ;$
(c) $\mathrm{ICl}_{2}^{-} ;$
(d) $\mathrm{PO}_{3}^{3-}$

David Collins

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Problem 29

Determine the geometries of the following ions:
(a) $\mathrm{S}_{2} \mathrm{O}_{3}^{2-}$
(b) $\mathrm{PO}_{4}^{3-} ;$
(c) $\mathrm{NO}_{3}^{-} ;$
(d) $\mathrm{NCO}^{-}$

David Collins

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Problem 30

Determine the geometries of the following molecules:
(a) $\mathrm{ClO}_{2} ;$ (b) $\mathrm{ClO}_{3} ;(\mathrm{c}) \mathrm{IF}_{3} ;(\mathrm{d}) \mathrm{SF}_{4}$

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Problem 31

Which of the following triatomic molecules, $\mathrm{O}_{3}, \mathrm{SO}_{2}$ $\mathrm{N}_{2} \mathrm{O}, \mathrm{S}_{2} \mathrm{O},$ and $\mathrm{CO}_{2},$ have the same molecular geometry?

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Problem 32

Which of the following species, $\mathrm{N}_{3}^{-}, \mathrm{O}_{3}, \mathrm{CO}_{2}, \mathrm{SCN}^{-}$ $\mathrm{CNO}^{-},$ and $\mathrm{NO}_{2}^{-},$ have the same molecular geometry?

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Problem 33

The anion $\mathrm{C}(\mathrm{CN})_{3}$. has a trigonal planar geometry about the central carbon atom. Draw Lewis structures for $\mathrm{C}(\mathrm{CN})_{3}^{-},$ including resonance forms, and determine which structure contributes the most to the bonding.

Massimo Antonelli

Massimo Antonelli

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Problem 34

The anion $\mathrm{C}\left(\mathrm{NO}_{2}\right)_{3}$ - has a trigonal planar geometry about the carbon atom. Draw Lewis structures for $\mathrm{C}\left(\mathrm{NO}_{2}\right)_{3}^{-}$ including resonance forms, and determine which structure contributes the most to the bonding.

David Collins

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Problem 35

The $C-N-C$ bond angles in tri(methyl)amine, $N\left(C H_{3}\right)_{3}$ are approximately 109 , whereas the $\mathrm{Si}-\mathrm{N}-$ Si bond angles in tri(silyl)amine, $\mathrm{N}\left(\mathrm{SiH}_{3}\right)_{3},$ are $120^{\circ},$ as shown in Figure P9.35. Explain the change in geometry when $\mathrm{Si}$ substitutes for C in this amine.

David Collins

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Problem 36

The geometry about nitrogen in $\mathrm{N}\left(\mathrm{CF}_{3}\right)_{3}$ and $\mathrm{N}\left(\mathrm{SCF}_{3}\right)_{3}$ is trigonal planar for both complexes, as shown in Figure P9.36. Draw Lewis structures for each that are consistent with the observed geometry. (Hint: For $\mathrm{N}\left(\mathrm{CF}_{3}\right)_{3}$ consider an ionic form $\left[\left(\mathrm{CF}_{3}\right)_{2} \mathrm{NCF}_{2}\right]^{+}[\mathrm{F}]^{-}$ )

David Collins

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Problem 37

For many years, it was believed that the noble gases could not form covalently bonded compounds. However, xenon reacts with fluorine and oxygen. Reaction between xenon tetrafluoride and fluoride ions produces the pentafluoroxenate anion: $$\mathrm{XeF}_{4}+\mathrm{F}^{-} \rightarrow \mathrm{XeF}_{5}^{-}$$ Draw Lewis structures for $\mathrm{XeF}_{4}$ and $\mathrm{XeF}_{5}^{-}$, and predict the geometry around xenon in $\mathrm{XeF}_{4} .$ The crystal structure of $\mathrm{XeF}_{5}^{-}$ compounds indicates a pentagonal bipyramidal orientation of valence pairs around Xe. Sketch the structure for $\mathrm{XeF}_{5}^{-}.$

David Collins

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Problem 38

The first compound containing a xenon-sulfur bond was isolated in $1998 .$ Draw a Lewis structure for HXeSH and determine its molecular geometry at Xe.

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Problem 39

The Cl-O distances in $\mathrm{ClO}_{2}^{+}, \mathrm{ClO}_{2},$ and $\mathrm{ClO}_{2}^{-}$ are found to be $131 \mathrm{pm}, 147 \mathrm{pm},$ and $156 \mathrm{pm},$ respectively. The corresponding $\mathrm{O}-\mathrm{Cl}-\mathrm{O}$ bond angles are $122^{\circ}, 118^{\circ},$ and $110^{\circ} .$ Draw Lewis structures consistent with these data.

David Collins

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Problem 40

Complete the Lewis structures of $\mathrm{SCNCl}_{3}$ in Figure P9. $40 .$ Is the geometry around nitrogen the same in both molecules?

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Problem 41

Explain the difference between a polar bond and a polar molecule.

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Problem 42

Must a polar molecule contain polar covalent bonds? Why or why not?

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Problem 43

Can a nonpolar molecule contain polar covalent bonds?

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Problem 44

Compare the dipole moments of $\mathrm{CO}_{2}$ and OCS.

David Collins

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Problem 45

Consider the following molecules: (a) $\mathrm{CCl}_{4} ;$ (b) $\mathrm{CHCl}_{3}$ (c) $\mathrm{CO}_{2} ;$ (d) $\mathrm{H}_{2} \mathrm{S} ;$ (e) $\mathrm{SO}_{2}$
a. Which of them contain polar bonds?
b. Which are polar molecules?
c. Which are nonpolar molecules?

David Collins

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Problem 46

Molecules in Space Simple diatomic molecules detected in interstellar space include $\mathrm{CO}, \mathrm{CS}, \mathrm{SiO}, \mathrm{SiS}, \mathrm{SO},$ and NO. Arrange these molecules in order of increasing dipole moment on the basis of the location of the constituent elements in the periodic table, and then calculate the electronegativity differences from the data in Figure 8.6.

David Collins

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Problem 47

Freon Ban Compounds containing carbon, chlorine, and fluorine are known as Freons or chlorofluorocarbons (CFCs). Widespread use of these substances was banned because of their effect on the ozone layer in the upper atmosphere. Which of the following CFCs are polar and which are nonpolar? (a) Freon $11\left(\mathrm{CFCl}_{3}\right) ;$ (b) Freon 12 $\left(\mathrm{CF}_{2} \mathrm{Cl}_{2}\right) ;(\mathrm{c})$ Freon $113\left(\mathrm{Cl}_{2} \mathrm{FCCF}_{2} \mathrm{Cl}\right).$

David Collins

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Problem 48

Which of the following chlorofluorocarbons (CFCs) are polar and which are nonpolar? (a) Freon $\mathrm{C} 318$ (C $_{4} \mathrm{F}_{8}$, cyclic structure); (b) Freon $1113\left(\mathrm{C}_{2} \mathrm{ClF}_{3}\right) ;$ (c) $\mathrm{Cl}_{2} \mathrm{HCCClF}_{2}.$

David Collins

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Problem 49

Which molecule in each of the pairs in Figure P9.49 has the larger dipole moment?
(a)(FIGURE CAN'T COPY) (b)(FIGURE CAN'T COPY) (c)(FIGURE CAN'T COPY)

David Collins

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Problem 50

Which molecule in each of the following pairs has the larger dipole moment? (a) $\mathrm{BF}_{3}$ or $\mathrm{BCl}_{3} ;$ (b) $\mathrm{BCl}_{2} \mathrm{F}$ or $\mathrm{BClF}_{2}$

David Collins

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Problem 51

Aluminum chloride has the Lewis structure shown in Figure $\mathrm{P} 9.51$
a. What is the geometry about the aluminum atom?
b. Is $A l_{2} C l_{6}$ polar or nonpolar?

David Collins

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Problem 52

Cleaning Silicon Chips Nitrogen trifluoride, $\mathrm{NF}_{3}$, is used in the electronics industry to clean surfaces. NF $_{3}$ is also a potent greenhouse gas.
a. Draw the Lewis structure of $\mathrm{NF}_{3}$ and determine its molecular geometry.
b. $\mathrm{BF}_{3}$ and $\mathrm{NF}_{3}$ both have three covalently bonded fluorine atoms around a central atom. Do they have the same dipole moment?
c. Could BF $_{3}$ also behave as a greenhouse gas?

David Collins

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Problem 53

Describe in your own words the differences between sigma and pi bonds.

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Problem 54

Why aren't the orbitals on isolated atoms hybridized?

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Problem 55

The bond angles in $\mathrm{PF}_{3}$ are $97.8^{\circ}.$
a. Explain the size of this angle by using hybrid orbitals.
b. Explain the size of this angle without using hybrid orbitals.

David Collins

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Problem 56

What combination of $s, p,$ and $d$ orbitals would we need to form four $\sigma$ and two $\pi$ bonds to a sulfur atom?

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Problem 57

What is the hybridization of nitrogen in each of the following ions and molecules? (a) $\mathrm{NO}_{2}^{+} ;$ (b) $\mathrm{NO}_{2}^{-}$
(c) $\mathrm{N}_{2} \mathrm{O} ;$ (d) $\mathrm{N}_{2} \mathrm{O}_{5} ;$ (e) $\mathrm{N}_{2} \mathrm{O}_{3}$

David Collins

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Problem 58

Identify the hybridization of the carbon atoms indicated by the arrows in the structures shown in Figure P9.58.

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Problem 59

Airbags Azides such as sodium azide, NaN $_{3},$ are used in automobile airbags as a source of nitrogen gas. Another compound with three nitrogen atoms bonded together is $\mathrm{N}_{3} \mathrm{F} .$ What differences are there in the arrangement of the electrons around the nitrogen atoms in the azide ion $\left(\overline{\mathrm{N}}_{3}^{-}\right)$ and $\mathrm{N}_{3} \mathrm{F}$ ? Is there a difference in the hybridization of the central nitrogen atom?

David Collins

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Problem 60

$\mathrm{N}_{3} \mathrm{F}$ decomposes to nitrogen and $\mathrm{N}_{2} \mathrm{F}_{2}$ by the following reaction: $$2 \mathrm{N}_{3} \mathrm{F} \rightarrow 2 \mathrm{N}_{2}+\mathrm{N}_{2} \mathrm{F}_{2}$$ $\mathrm{N}_{2} \mathrm{F}_{2}$ has two possible structures, as shown in Figure P9.60. Are the differences between these structures related to differences in the hybridization of nitrogen in $\mathrm{N}_{2} \mathrm{F}_{2} ?$ Identify the hybrid orbitals that account for the bonding in $\mathrm{N}_{2} \mathrm{F}_{2} .$ Are they the same as those in acetylene, $\mathrm{C}_{2} \mathrm{H}_{2} ?$

David Collins

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Problem 61

How does the hybridization of the sulfur atom change in the series $\mathrm{SF}_{2}, \mathrm{SF}_{4},$ and $\mathrm{SF}_{6} ?$

David Collins

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Problem 62

How does the hybridization of the central atom change in the series $\mathrm{CO}_{2}, \mathrm{NO}_{2}, \mathrm{O}_{3},$ and $\mathrm{ClO}_{2} ?$

David Collins

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Problem 63

Minoxidil The drug minoxidil was originally developed for treating high blood pressure but is now used primarily for treating hair loss. The Lewis structure of minoxidil is shown in Figure P9.63. Complete the Lewis structure by adding lone pairs where needed. Assign formal charges to the nitrogen and oxygen highlighted in red. Describe the bonding around the nitrogen in the N-O group.

David Collins

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Problem 64

Draw the Lewis structure of the chlorite ion, $\mathrm{ClO}_{2}^{-}$ which is used as a bleaching agent. Include all resonance structures in which formal charges are closest to zero. What is the shape of the ion? Suggest a hybridization scheme for the central chlorine atom that accounts for the structures you have drawn.

David Collins

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Problem 65

Perchlorate lon and Human Health Perchlorate ion adversely affects human health by interfering with the uptake of iodine in the thyroid gland, but because of this behavior, it also provides a useful medical treatment for hyperthyroidism, or overactive thyroid. Draw the Lewis structure of the perchlorate ion, $\mathrm{ClO}_{4}^{-} .$ Include all resonance structures in which formal charges are closest to zero. What is the shape of the ion? Suggest a hybridization scheme for the central chlorine atom that accounts for this shape.

David Collins

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Problem 66

Draw a Lewis structure for $\mathrm{CF}_{3} \mathrm{PCF}_{2}$ where the fluorine atoms are all bonded to carbon atoms. Determine its molecular geometry at $P$ and the hybridization of the phosphorus atom.

David Collins

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Problem 67

Synthesis of the first compound of argon was reported in 2000. HArF was made by reacting Ar with HF. Draw a Lewis structure for HArF, and determine the hybridization of Ar in this molecule.

David Collins

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Problem 68

The Lewis structure of $\mathrm{N}_{4} \mathrm{O},$ with the skeletal structure $\mathrm{O}-\mathrm{N}-\mathrm{N}-\mathrm{N}-\mathrm{N},$ contains one $\mathrm{N}-\mathrm{N}$ single bond, one $\mathrm{N}=\mathrm{N}$ double bond, and a $\mathrm{N} \equiv \mathrm{N}$ triple bond. Is the hybridization of all the nitrogen atoms the same?

Susan Hallstrom

Susan Hallstrom

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Problem 69

The trifluorosulfate anion was isolated in 1999 as the tetramethylammonium salt $\left[\left(\mathrm{CH}_{3}\right)_{4} \mathrm{N}\right]^{+}\left[\mathrm{SO}_{2} \mathrm{F}_{3}\right]^{-}.$
a. Determine the geometry around the nitrogen atom in the cation and describe the $C-N$ bonding according to valence bond theory.
b. The $S-O$ bond lengths in the anion are both $143 \mathrm{pm}$. Draw the Lewis structure that is consistent with this bond length.
c. What is the molecular geometry of the anion?

David Collins

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Problem 70

Treating Diabetes The drug metformin (Figure P9.70) has been used to treat type 2 diabetes for a half-century by suppressing glucose production. Metformin contains five nitrogen atoms. Determine the geometry around each nitrogen atom, and describe the bonding according to valence bond theory.

David Collins

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Problem 71

What features do Lewis structures, Kekulé structures, condensed structures, and carbon-skeleton structures share in common? What features differentiate these four kinds of structures?

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Problem 72

Explain why alkanes don't have optical isomers.

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Problem 73

Can molecules with more than one central atom have resonance forms? Explain your answer.

David Collins

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Problem 74

Can hybrid orbitals be associated with more than one atom? Explain your answer.

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Problem 75

Are resonance structures examples of electron delocalization? Explain your answer.

David Collins

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Problem 76

Can $s p^{2}$ and $s p$ hybridized carbon atoms be chiral centers? Explain your answer.

David Collins

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Problem 77

Which of the following objects are chiral? (a) a baseball bat with no lettering on it; (b) a pair of scissors; (c) a boot; (d) a fork

David Collins

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Problem 78

Why is it difficult to assign a single geometry to a molecule with more than one central atom?

David Collins

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Problem 79

Bombykol is the compound synthesized by female silkworm moths to attract mates. Convert the carbon-skeleton structure in Figure $\mathrm{P} 9.79$ to a condensed structure.

David Collins

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Problem 80

Fucoserratene is the compound synthesized by a brown alga to reproduce. Convert the carbonskeleton structure in Figure P9.80 to a condensed structure.

David Collins

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Problem 81

Sex Hormones Progesterone (Figure P9.81a) is a hormone involved in regulating menstrual cycles and pregnancy, and testosterone (Figure $9.81 \mathrm{b}$ ) is the primary male sex hormone. What functional groups do these two hormones have in common? (a) (FIGURE CAN'T COPY) (b) (FIGURE CAN'T COPY)

David Collins

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Problem 82

Steroid Hormones Cortisone (Figure $\mathrm{P} 9.82$ ) is a steroid produced by the body in response to stress. It suppresses the immune system and can be administered as a drug to reduce inflammation, pain, and swelling. Identify all the functional groups in cortisone.

David Collins

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Problem 83

Unsaturated Fats Oleic acid (Figure $\mathrm{P} 9.83$ ) is a fat derived from olive oil. Write a condensed structure for oleic acid.

David Collins

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Problem 84

Draw a carbon-skeleton structure for oleic acid (Figure $\mathrm{P} 9.83)$

David Collins

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Problem 85

Prozac Fluoxetine (Figure $\mathrm{P} 9.85$ ) is an antidepressant medication sold commercially as Prozac. Circle the delocalized $\pi$ electrons in fluoxetine.

David Collins

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Problem 86

Figure P9.86 shows the carbon-skeleton structure of the antifungal compound capillin. Are there delocalized electrons in capillin? If so, identify them.

David Collins

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Problem 87

Artificial Sweeteners Acesulfame potassium is one of many artificial sweeteners used in food. It is 200 times sweeter than sugar and has the structure shown in Figure P9.87. What is the geometry at each of the atoms in the sixmembered ring? Which atomic or hybrid orbitals overlap to form the $\mathrm{C}-\mathrm{O}$ and $\mathrm{C}-\mathrm{N}$ bonds? In which atomic or hybrid orbital is the extra electron on $\mathrm{N}$ located?

David Collins

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Problem 88

First Artificial Sweetner Saccharin (Figure $\mathrm{P} 9.88)$ was the first artificial sweetener, discovered in $1879 .$ Like acesulfame potassium, it contains a sulfur atom adjacent to a nitrogen atom. Why don't all the atoms in the five-membered ring lie in the same plane? Why is it difficult to explain the bonding between $\mathrm{S}$ and $\mathrm{O}$ by using the hybrid orbitals described in Section $9.4 ?$

David Collins

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Problem 89

Which molecules in Figure P9.89 are chiral?

David Collins

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Problem 90

Which molecules in Figure P9.90 are chiral?

David Collins

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Problem 91

Do all $\sigma$ molecular orbitals result from the overlap of $s$ atomic orbitals? Explain your answer.

David Collins

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Problem 92

Do all $\pi$ molecular orbitals result from the overlap of $p$ atomic orbitals? Explain your answer.

David Collins

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Problem 93

Are s atomic orbitals with different principal quantum numbers $(n)$ as likely to overlap and form MOs as s atomic orbitals with the same value of $n ?$ Explain your answer.

David Collins

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Problem 94

Which atomic orbitals are more likely to mix to form a set of molecular orbitals-a $2 s$ and a $3 p$ orbital or a $4 s$ and a $5 p$ orbital?

David Collins

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Problem 95

Why might some molecules with even numbers of valence electrons be paramagnetic?

David Collins

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Problem 96

How does the molecular orbital diagram for a homonuclear diatomic species differ from that of a heteronuclear diatomic species?

David Collins

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Problem 97

How does the sea-of-electrons model (Chapter 8 ) explain the high electrical conductivity of gold? How does band theory explain this?

David Collins

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Problem 98

Some scientists believe that the solid hydrogen that forms at very low temperatures and high pressures may conduct electricity. Is this hypothesis supported by band theory?

David Collins

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Problem 99

Describe in general terms the differences in composition and conduction between n-type and p-type semiconductors.

David Collins

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Problem 100

How might doping of silicon with germanium affect the conductivity of silicon?

David Collins

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Problem 101

Make a sketch showing how two 1 s orbitals overlap to form a $\sigma_{1s}$ bonding molecular orbital and a $\sigma_{1 s}^{*}$ antibonding molecular orbital.

David Collins

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Problem 102

Make a sketch showing how two $2 p_{y}$ orbitals overlap "sideways" to form a $\pi_{2 p}$ bonding molecular orbital and a $\pi_{2 p}^{*}$ antibonding molecular orbital.

David Collins

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Problem 103

Consider the following molecular ions: $\mathrm{N}_{2}^{+}, \mathrm{O}_{2}^{+}, \mathrm{C}_{2}^{+},$ and $\mathrm{Br}_{2}^{2-} .$ Using MO theory, (a) write their orbital electron configuration; (b) predict their bond orders; (c) state whether you expect any of these species to exist.

David Collins

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Problem 104

Diatomic noble gas molecules, such as $\mathrm{He}_{2}$ and $\mathrm{Ne}_{2},$ do not exist.
a. Write their orbital electron configurations.
b. Does removing one electron from each of these molecules create molecular ions $$\left(\mathrm{He}_{2}^{+} \text {and } \mathrm{Ne}_{2}^{+}\right)$$ that are more stable than $\mathrm{He}_{2}$ and $\mathrm{Ne}_{2} ?$

David Collins

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Problem 105

Which of the following molecular ions is expected to have one or more unpaired electrons?
(a) $\mathrm{N}_{2}^{+} ;$ (b) $\mathrm{O}_{2}^{+} ;$ (c) $\mathrm{C}_{2}^{2+}$ (d) $\mathrm{Br}_{2}^{2-} ;$ (e) $\mathrm{O}_{2}^{-} ;$ (f) $\mathrm{O}_{2}^{2-} ;$ (g) $\mathrm{N}_{2}^{2-} ;$ (h) $\mathrm{F}_{2}^{+}$

David Collins

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Problem 106

Which of the following molecular ions have electrons in $\pi$ antibonding orbitals? (a) $\mathrm{O}_{2}^{-} ;$ (b) $\mathrm{O}_{2}^{2-} ;$ (c) $\mathrm{N}_{2}^{2-} ;$ (d) $\mathrm{F}_{2}^{+}$ (e) $\mathrm{N}_{2}^{+} ;$ (f) $\mathrm{O}_{2}^{+} ;(\mathrm{g}) \mathrm{C}_{2}^{2+} ;$ (h) $\mathrm{Br}_{2}^{2+}$

David Collins

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Problem 107

The odd-electron molecule ClO affects the atmospheric chemistry of chlorofluorocarbons as illustrated by the reaction (where the $^{*}$ indicates an excited-state oxygen atom): $$\mathrm{CF}_{2} \mathrm{Cl}_{2}+\mathrm{O}^{*} \rightarrow \mathrm{ClO}+\mathrm{CF}_{2} \mathrm{Cl}$$ Draw a molecular orbital diagram for ClO. Is the odd electron in a bonding or antibonding orbital?

David Collins

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Problem 108

The elusive molecule boron monoxide, $\mathrm{BO},$ can be stabilized by bonding to platinum. Draw a molecular orbital diagram for BO. Is the odd electron in a bonding or antibonding orbital?

David Collins

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Problem 109

For which of the following diatomic molecules does the bond order increase with the gain of two electrons, forming the corresponding anion with a $2-$ charge? a. $\mathrm{B}_{2}+2 \mathrm{e}^{-} \rightarrow \mathrm{B}_{2}^{2-}$
b. $C_{2}+2 e^{-} \rightarrow C_{2}^{2-}$ c. $\mathrm{N}_{2}+2 \mathrm{e}^{-} \rightarrow \mathrm{N}_{2}^{2-}$
d. $\mathrm{O}_{2}+2 \mathrm{e}^{-} \rightarrow \mathrm{O}_{2}^{2-}$

David Collins

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Problem 110

For which of the following diatomic molecules does the bond order increase with the loss of two electrons, forming the corresponding cation with a $2+$ charge? a. $\quad B_{2} \rightarrow B_{2}^{2+}+2 e^{-}$ b. $C_{2} \rightarrow C_{2}^{2+}+2 e^{-}$ c. $\mathrm{N}_{2} \rightarrow \mathrm{N}_{2}^{2+}+2 \mathrm{e}^{-}$ d. $\mathrm{O}_{2} \rightarrow \mathrm{O}_{2}^{2+}+2 \mathrm{e}^{-}$

David Collins

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Problem 111

Do the $1+$ cations of homonuclear diatomic molecules of the second-row elements always have shorter bond lengths than the corresponding neutral molecules?

David Collins

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Problem 112

Do any of the anions of the homonuclear diatomic molecules formed by $\mathrm{B}, \mathrm{C}, \mathrm{N}, \mathrm{O},$ and $\mathrm{F}$ have shorter bond lengths than those of the corresponding neutral molecules? Consider only the anions with $1-$ or $2-$ charge.

David Collins

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Problem 113

Thin films of doped diamond hold promise as semiconductor materials. Trace amounts of nitrogen impart a yellow color to otherwise colorless pure diamonds.
a. Are nitrogen-doped diamonds examples of semiconductors that are $p$ -type or $n$ -type?
b. Draw a picture of the band structure of diamond to indicate the difference between pure diamond and N-doped (nitrogen-doped) diamond.
"c. N-doped diamonds absorb violet light at about $425 \mathrm{nm}$ What is the magnitude of $E_{\mathrm{g}}$ that corresponds to this wavelength?

David Collins

Numerade Educator

Problem 114

Hope Diamond Trace amounts of boron give diamonds (including the Smithsonian's Hope Diamond) a blue color (Figure $\mathrm{P} 9.114).$
a. Are boron-doped diamonds examples of semiconductors that are $p$ -type or n-type?
b. Draw a picture of the band structure of diamond to indicate the difference between pure diamond and B-doped diamond.
c. What is the band gap in energy if blue diamonds absorb red-orange light with a wavelength of 675 nm?

David Collins

Numerade Educator

Problem 115

Draw the Lewis structure for the two ions in ammonium perchlorate $\left(\mathrm{NH}_{4} \mathrm{ClO}_{4}\right),$ which is used as a propellant in solid fuel rockets, and determine the molecular geometries of the two polyatomic ions.

David Collins

Numerade Educator

Problem 116

Arsenic-Based DNA? The waters of Mono Lake in the eastern Sierra Mountains of California (Figure $\mathrm{P} 9.116$ ) are rich in arsenate ion $\left(\mathrm{As} \mathrm{O}_{4}^{3-}\right) .$ Some biochemists have proposed that microorganisms in this environment actually incorporate arsenate into their DNA in place of the phosphate ion $\left(\mathrm{PO}_{4}^{3-}\right) .$ Draw the Lewis structure of the arsenate ion that yields the most favorable formal charges.Predict the angles between the arsenic-oxygen bonds in the arsenate anion.

David Collins

Numerade Educator

Problem 117

Consider the molecular structure of the amino acid glycine shown in Figure P9.117. What is the angle formed by the $\mathrm{N}-\mathrm{C}-\mathrm{C}$ bonds in this structure? What are the $\mathrm{O}-\mathrm{C}=\mathrm{O}$ and $\mathrm{C}-\mathrm{O}-\mathrm{H}$ bond angles?

David Collins

Numerade Educator

Problem 118

$\mathrm{Cl}_{2} \mathrm{O}_{2}$ may play a role in ozone depletion in the stratosphere. In the laboratory, a reaction between $\mathrm{ClO}_{2} \mathrm{~F}$ and $\mathrm{AlCl}_{3}$ produces $\mathrm{Cl}_{2} \mathrm{O}_{2}$ and $\mathrm{AlCl}_{2} \mathrm{~F}$. Draw the Lewis structure for $\mathrm{Cl}_{2} \mathrm{O}_{2}$ on the basis of the skeletal structure in Figure $\mathrm{P} 9.118$. What is the geometry about the central chlorine atom?

David Collins

Numerade Educator

Problem 119

Bombardment of $\mathrm{Cl}_{2} \mathrm{O}_{2}$ molecules (Figure $\mathrm{P} 9.119$ ) with intense radiation is thought to produce the two compounds with the skeletal structures shown in Figure P9.119.
a. Do both of these molecules have linear geometry? Explain your answer.
b. Do they have the same dipole moment? Explain your answer.

David Collins

Numerade Educator

Problem 120

Complete the Lewis structure for the cyclic structure of $\mathrm{Cl}_{2} \mathrm{O}_{2}$ shown in Figure P9.120.
a. Is the cyclic $\mathrm{Cl}_{2} \mathrm{O}_{2}$ molecule planar?
b. Is the molecule polar or nonpolar?

David Collins

Numerade Educator

Problem 121

In 1999 the $\mathrm{ClO}^{+}$ ion, a potential contributor to stratospheric ozone depletion, was isolated in the laboratory.
a. Draw the Lewis structure for $\mathrm{ClO}^{+}$
b. Using the molecular orbital diagram in Figure P9.121, determine the order of the $\mathrm{Cl}-\mathrm{O}$ bond in $\mathrm{ClO}^{+}.$
(FIGURE CAN'T COPY)

David Collins

Numerade Educator

Problem 122

The molecule trinitramide, $\mathrm{N}\left(\mathrm{NO}_{2}\right)_{3},$ was first prepared in late 2010 by chemists in Sweden. Draw Lewis structures for trinitramide and predict the geometry about the central nitrogen atom. Do all resonance forms of $\mathrm{N}\left(\mathrm{NO}_{2}\right)_{3}$ have the same geometry?

David Collins

Numerade Educator

Problem 123

Cola Beverages Phosphoric acid imparts a tart flavor to cola beverages. The skeletal structure of phosphoric acid is shown in Figure P9.123. Complete the Lew structure for phosphoric acid in which formal charges are closest to zero. What is the molecular geometry around the phosphorus atom in your structure?

David Collins

Numerade Educator

Problem 124

The fluoroaluminate anions $\mathrm{AlF}_{4}^{-}$ and $\mathrm{AlF}_{6}^{3-}$ have been known for more than a century, but the structure of the pentafluoroaluminate ion, $\mathrm{AlF}_{5}^{2-},$ was not determined until 2003. Draw the Lewis structures for AlF $_{3},$ AlF $_{4}^{-}$, $\mathrm{AlF}_{5}^{2-},$ and $\mathrm{AlF}_{6}^{3-} .$ Determine the molecular geometry of each molecule or ion. Describe the bonding in $\mathrm{AlF}_{3}$ $\mathrm{AlF}_{4}^{-}, \mathrm{AlF}_{5}^{2-},$ and $\mathrm{AlF}_{6}^{3-}$ by using valence bond theory.

David Collins

Numerade Educator

Problem 125

Thermally unstable compounds can sometimes be synthesized using matrix isolation methods in which the compounds are isolated in a nonreactive medium such as frozen argon. The reaction of boron with carbon monoxidn produces compounds with these skeletal structures: $\mathrm{B}-\mathrm{B}-\mathrm{C}-\mathrm{O}$ and $\mathrm{O}-\mathrm{C}-\mathrm{B}-\mathrm{B}-\mathrm{C}-\mathrm{O} .$ For each of these compounds, draw the Lewis structure that minimizes formal charges. Do any of your structures contain atoms with incomplete octets? Predict the molecular geometries of BBCO and OCBBCO.

David Collins

Numerade Educator

Problem 126

The products of the reaction between boron and NO can be trapped in solid argon matrices. Among the products is BNO. Draw the Lewis structure for BNO, including any resonance forms. Assign formal charges and predict which structure provides the best description of the bonding in this molecule. Do any of your structures contain atoms without complete octets? Predict the molecular geometry of BNO.

David Collins

Numerade Educator

Problem 127

Compounds May Help Prevent Cancer Broccoli, cabbage, and kale contain compounds that break down in the human body to form isothiocyanates, whose presence may reduce the risk of certain types of cancer. The simplest isothiocyanate is methyl isothiocyanate, $\mathrm{CH}_{3} \mathrm{NCS}$. Draw the Lewis structure for $\mathrm{CH}_{3} \mathrm{NCS}$, including all resonance forms. Assign formal charges and determine which structure is likely to contribute the most to bonding. Predict the molecular geometry of the molecule at both carbon atoms.

David Collins

Numerade Educator

Problem 128

Toxic to Insects and People Methyl thiocyanate $\left(\mathrm{CH}_{3} \mathrm{SCN}\right)$ is used as an agricultural pesticide and fumigant. It is slightly water soluble and is readily absorbed through the skin; it is highly toxic if ingested. Its toxicity stems in part from its metabolism to cyanide ion. Draw three resonance structures for methyl thiocyanate. Assign formal charges and predict which structure would be the most stable. Predict the molecular geometry of the molecule at both carbon atoms.

David Collins

Numerade Educator

Problem 129

Skunks The pungent smell of skunk spray is detected by receptors in the nose when the skunk secretes butanethiol, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{SH} .$ Draw a carbon-skeleton structure for butanethiol.

David Collins

Numerade Educator

Problem 130

Grapefruit Not all sulfur-containing compounds have unpleasant aromas. Figure $\mathrm{P} 9.130$ shows the structure of the compound primarily responsible for the aroma of grapefruit. Identify the chiral carbon in this structure.

David Collins

Numerade Educator

Problem 131

Borazine, $\mathrm{B}_{3} \mathrm{N}_{3} \mathrm{H}_{6}$ (a cyclic compound with alternating $\mathrm{B}$ and $\mathrm{N}$ atoms in the ring), is isoelectronic with benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right) .$ Are there delocalized $\pi$ electrons in borazine? (FIGURE CAN'T COPY)

David Collins

Numerade Educator

Problem 132

Unlike $\mathrm{O}_{2},$ sulfur monoxide (SO) is highly unstable, decomposing to a mixture of $\mathrm{S}_{2} \mathrm{O}$ and $\mathrm{O}_{2}$ in less than 1 second. Using the $\mathrm{O}_{2 \mathrm{s}}, \mathrm{O}_{2 p}, \mathrm{S}_{3, \mathrm{s}}$ and $\mathrm{S}_{3 p}$ atomic orbitals, construct an approximate molecular orbital diagram for SO. Is SO diamagnetic or paramagnetic?

David Collins

Numerade Educator

Problem 133

Some chemists think HArF consists of $\mathrm{H}^{+}$ ions and $\mathrm{Ar}$ $\mathrm{F}^{-}$ ions. Using an appropriate MO diagram, determine the bond order of the $\mathrm{Ar}-\mathrm{F}$ bond in $\mathrm{ArF}^{-}.$

David Collins

Numerade Educator

Problem 134

Assume that HArF is a molecular compound.
a. Draw its Lewis structure.
b. What are the formal charges on $\mathrm{Ar}$ and $\mathrm{F}$ in the structure you drew?
c. What is the shape of the molecule?
d. Is HArF polar?

David Collins

Numerade Educator

Problem 135

Which of the following unstable nitrogen oxides, $\mathrm{N}_{2} \mathrm{O}_{2}$ $\mathrm{N}_{2} \mathrm{O}_{5},$ and $\mathrm{N}_{2} \mathrm{O}_{3},$ are polar molecules? $\left(\mathrm{N}_{2} \mathrm{O}_{2} \text { and } \mathrm{N}_{2} \mathrm{O}_{3}\right.$ have $\left.\mathrm{N}-\mathrm{N} \text { bonds; } \mathrm{N}_{2} \mathrm{O}_{5} \text { does not. }\right)$

David Collins

Numerade Educator

Problem 136

Explain why $\mathrm{O}_{2}$ is paramagnetic.

David Collins

Numerade Educator

Problem 137

Using an appropriate molecular orbital diagram, show that the bond order in the disulfide anion $\mathrm{S}_{2}^{2-}$ is equal to $1 .$ Is $\mathrm{S}_{2}^{2-}$ diamagnetic or paramagnetic?

David Collins

Numerade Educator

Problem 138

Use molecular orbital diagrams to determine the bond order of the peroxide $\left(\mathrm{O}_{2}^{2-}\right)$ and superoxide $\left(\mathrm{O}_{2}^{-}\right)$ ions. Are these bond order values consistent with those predicted from Lewis structures?

David Collins

Numerade Educator

Problem 139

Elemental sulfur has several allotropic forms, including cyclic $\mathrm{S}_{8}$ molecules. What is the orbital hybridization of sulfur atoms in this allotrope? The bond angles are about $108^{\circ}.$

David Collins

Numerade Educator

Problem 140

Which $3 d$ atomic orbitals have the proper orientation to overlap with a $4 p_{z}$ atomic orbital?

David Collins

Numerade Educator

Problem 141

Ozone $\left(\mathrm{O}_{3}\right)$ has a dipole moment $(0.54 \mathrm{D}) .$ How can a molecule with only one kind of atom have a dipole moment?

David Collins

Numerade Educator

Problem 142

The bond angle in $\mathrm{H}_{2} \mathrm{O}$ is 104.5 $^\circ$; the bond angles in $\mathrm{H}_{2} \mathrm{S}$ $\mathrm{H}_{2} \mathrm{Se},$ and $\mathrm{H}_{2} \mathrm{Te}$ are very close to $90^{\circ} .$ Which theory would you apply to describe the geometry in $\mathrm{H}_{2} \mathrm{S}, \mathrm{H}_{2} \mathrm{Se},$ and $\mathrm{H}_{2} \mathrm{Te}:$ VSEPR? Valence bond without invoking hybrid orbitals? Valence bond theory, using hybrid orbitals? Why?

David Collins

Numerade Educator

Problem 143

Garlic Garlic contains the molecule alliin (Figure $\mathrm{P} 9.143$ ). When garlic is crushed or chopped, a reaction occurs that converts alliin into the molecule allicin, which is primarily responsible for the aroma we associate with garlic.
a. Describe the molecular geometry about the sulfur atoms in both compounds.
b. Do any of the sulfur atoms in allicin have the same geometry as the sulfur atoms in the volatile sulfur compounds that cause bad breath $\left(\mathrm{H}_{2} \mathrm{S}, \mathrm{CH}_{3}-\mathrm{SH}$, \right. and $\left.\mathrm{CH}_{3}-\mathrm{S}-\mathrm{CH}_{3}\right) ?$
(FIGURE CAN'T COPY)

David Collins

Numerade Educator