Chemistry: The Molecular Nature of Matter

Neil D. Jespersen, James E. Brady, Alison Hyslop

Chapter 9

Theories of Bonding and Structure - all with Video Answers

Educators

Chapter Questions

Problem 1

Sketch the following molecular shapes and give the various bond angles in the structures:
(a) planar triangular, (b) tetrahedral, (c) octahedral.

Arpit Gupta

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Problem 2

Sketch the following molecular shapes and give the bond angles in the structures: (a) linear, (b) trigonal bipyramidal.

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Problem 3

What is the underlying principle on which the VSEPR model is based?

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Problem 4

What is an electron domain? How are nonbonding and double bonds described by electron domains?

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Problem 5

How many bonding domains and how many nonbonding domains are there in a molecule of formaldehyde, HCHO?

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Problem 6

Sketch the following molecular shapes and give the various bond angles in the structure:
(a) T-shaped,
(b) seesaw shaped, and (c) square pyramidal.

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Problem 7

What arrangements of domains around an atom are expected when there are
(a) three domains,
(b) six domains, (c) four domains, or (d) five domains?

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Problem 8

Why is it useful to know the polarities of molecules?

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Problem 9

How do we indicate a bond dipole when we draw the structure of a molecule?

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Problem 10

Under what conditions will a molecule be polar?

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Problem 11

What condition must be met if a molecule having polar bonds is to be non polar?

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Problem 12

Use a drawing to show why the $\mathrm{SO}_{2}$ molecule is polar.

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Problem 13

What is meant by orbital overlap?

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Problem 14

How is orbital overlap related to bond energy?

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Problem 15

Use sketches of orbitals to describe how VB theory would explain the formation of the $\mathrm{H}-\mathrm{Br}$ bond in hydrogen bromide. How many lone pairs of electrons would be found on each?

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Problem 16

Why do atoms usually use hybrid orbitals for bonding rather than pure atomic orbitals?

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Problem 17

Sketch figures that illustrate the directional properties of the following hybrid orbitals: (a) $s p$, (b) $s p^{2}$, (c) $s p^{3}$.

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Problem 18

Sketch figures that illustrate the directional properties of (a) $s p^{3} d$ (b) $s p^{3} d^{2}$.

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Problem 19

Why do Period 2 elements never use $s p^{3} d$ or $s p^{3} d^{2}$ hybrid orbitals for bond formation?

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Problem 20

What relationship is there, if any, between Lewis structures and the valence bond descriptions of molecules?

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Problem 21

How can the VSEPR model be used to predict the hybridization of an atom in a molecule?

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Problem 22

If the central oxygen in the water molecule did not use sp hybridized orbitals (or orbitals of any other kind of hybridization), what would be the expected bond angle in $\mathrm{H}_{2} \mathrm{O}$ ?

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Problem 23

Using orbital diagrams, describe how sp $^{3}$ hybridization occurs in each atom: (a) carbon, (b) nitrogen, (c) oxygen. If these elements use $s p^{3}$ hybrid orbitals to form bonds, how many lone pairs of electrons would be found on each?

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Problem 24

Sketch the way the orbitals overlap to form the bonds in each of the following: (a) $\mathrm{CH}_{4},$ (b) $\mathrm{NH}_{3}$, (c) $\mathrm{H}_{2} \mathrm{O}$. (Assume the central atom uses hybrid orbitals.)

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Problem 25

We explained the bond angles of $107^{\circ}$ in $\mathrm{NH}_{3}$ by using $s p^{3}$ hybridization of the central nitrogen atom. If unhybridized $p$ orbitals of nitrogen were used to overlap with 1 s orbitals of each hydrogen, what would the $\mathrm{H}-\mathrm{N}-\mathrm{H}$ bond angles be? Explain.

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Problem 26

Using sketches of orbitals and orbital diagrams, describe $s p^{2}$ hybridization of (a) boron and (b) carbon.

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Problem 27

What two basic shapes have hybridizations that include $\bar{d}$ orbitals??

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Problem 28

The ammonia molecule, $\mathrm{NH}_{3}$, can combine with a hydrogen ion, $\mathrm{H}^{+}$ (which has an empty 1 s orbital), to form the ammonium ion, $\mathrm{NH}_{4}^{+}$. (This is how ammonia can neutralize acid and therefore function as a base.) Sketch the geometry of the ammonium ion, indicating the bond angles.

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Problem 29

How does the geometry around $\mathrm{B}$ and $\mathrm{O}$ change in the following reaction? How does the hybridization of each atom change?

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Problem 30

How do $\sigma$ and $\pi$ bonds differ?

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Problem 31

Why can free rotation occur easily around a $\sigma$ -bond axis but not around a $\pi$ -bond axis?

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Problem 32

Using sketches, describe the bonds and bond angles in ethene, $\mathrm{C}_{2} \mathrm{H}_{4}$

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Problem 33

Sketch the way the bonds form in acetylene, $\mathrm{C}_{2} \mathrm{H}_{2}$.

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Problem 34

How does VB theory treat the benzene molecule? (Draw sketches describing the orbital overlaps and the bond angles.)

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Problem 35

Why is the higher-energy MO in $\mathrm{H}_{2}$ called an antibonding orbital? Make a sketch of the bonding and antibonding orbitals in $\mathrm{H}_{2}$.

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Problem 36

Below is an illustration showing two $3 d$ orbitals about to overlap. The drawings also show the algebraic signs of the wave functions for both orbitals in this combination. Will this combination of orbitals produce a bonding or an antibonding $\mathrm{MO}$ ? Sketch the shape of the $\mathrm{MO}$.

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Problem 37

Will the combination of $3 d$ orbitals in Question 9.36 yield a $\sigma$ or $\pi$ type of $M O$ ? Explain.

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Problem 38

Explain why $\mathrm{He}_{2}$ does not exist but $\mathrm{H}_{2}$ does.

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Problem 39

How does MO theory account for the paramagnetism of $\mathrm{O}_{2} ?$

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Problem 40

On the basis of MO theory, explain why $\mathrm{Li}_{2}$ molecules can exist but $\mathrm{Be}_{2}$ molecules cannot. Could the ion $\mathrm{Be}_{2}{ }^{+}$ exist?

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Problem 41

What relationship is there between bond order and bond energy?

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Problem 42

Sketch the shapes of the $\pi_{2 p_{1}}$ and $\pi_{2 p_{r}}^{*}$ MOs.

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Problem 43

What is the theoretical basis of both valence bond $(\mathrm{VB})$ theory and molecular orbital (MO) theory?

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Problem 44

What shortcomings of Lewis structures and VSEPR theory do $\mathrm{VB}$ and $\mathrm{MO}$ theories attempt to overcome?

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Problem 45

What is the main difference in the way VB and MO theories view the bonds in a molecule?

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Problem 46

What is a delocalized MO? Explain, in terms of orbital overlap, why delocalized MOs are able to form in the benzene molecule.

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Problem 47

What effect does delocalization have on the stability of the electronic structure of a molecule?

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Problem 48

What is delocalization energy? How is it related to resonance energy?

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Problem 49

What is a conduction band? What is a valence band?

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Problem 50

What is required to form a conduction band?

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Problem 51

On the basis of the band theory of solids, how do conductors, insulators, and semiconductors differ?

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Problem 52

Why does electrical conductivity in semiconductors increase with increasing temperature?

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Problem 53

In calcium, why can't electrical conduction take place by movement of electrons through the $2 s$ energy band? How does calcium conduct electricity?

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Problem 54

What are allotropes? How do they differ from isotopes?

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Problem 55

Why are the Period 2 elements able to form much stronger $\pi$ bonds than the nonmetals of Period 3 ? Why does a Period 3 nonmetal prefer to form all $\sigma$ bonds instead of one $\sigma$ bond and several $\pi$ bonds?

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Problem 56

Even though the nonmetals of Periods $3,4,$ and 5 do not tend to form $\pi$ bonds between like atoms, each of the halogens is able to form diatomic molecules $\left(\mathrm{Cl}_{2}, \mathrm{Br}_{2}, \mathrm{I}_{2}\right)$ Why?

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Problem 57

Which of the nonmetals occur in nature in the form of isolated atoms?

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Problem 58

Describe the structure of diamond. What kind of hybrid orbitals does carbon use to form bonds in diamond? What is the geometry around carbon in this structure?

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Problem 59

Describe the structure of graphene. What kind of hybrid orbitals does carbon use in the formation of the molecular framework of graphene?

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Problem 60

How is the structure of graphite related to the structure of graphene?

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Problem 61

Describe the $\mathrm{C}_{60}$ molecule. What is it called? What name is given to the series of similar substances?

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Problem 62

How is the structure of a carbon nanotube related to the structure of graphene?

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Problem 63

What is the molecular structure of silicon? Suggest a reason why silicon doesn't form an allotrope that's similar in structure to graphite.

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Problem 64

Make a sketch that describes the molecular structure of white phosphorus.

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Problem 65

What are the different allotropes of phosphorus?

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Problem 66

What are the $\mathrm{P}-\mathrm{P}-\mathrm{P}$ bond angles in the $\mathrm{P}_{4}$ molecule? If phosphorus uses $p$ orbitals to form the phosphorusphosphorus bonds, what bond angle would give the best orbital overlap? On the basis of your answers to these two questions, explain why $\mathrm{P}_{4}$ is so chemically reactive.

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Problem 67

What structure has been proposed for red phosphorus? How do the reactivities of red and white phosphorus compare?

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Problem 68

What is the molecular structure of black phosphorus? In what way does the structure of black phosphorus resemble that of graphite?

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Problem 69

What are the two allotropes of oxygen?

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Problem 70

Draw the Lewis structure for $\mathrm{O}_{3}$. Is the molecule linear, based on the VSEPR model? Assign formal charges to the atoms in the Lewis structure. Does this suggest the molecule is polar or nonpolar?

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Problem 71

What beneficial function does ozone serve in earth's upper atmosphere?

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Problem 72

What is the molecular structure of sulfur in its most stable allotropic form?

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Problem 73

Predict the shapes of (a) $\mathrm{NH}_{2}^{-}$, (b) $\mathrm{CO}_{3}^{2-}$, (c) $\mathrm{IF}_{3},$ (d) $\mathrm{Br}_{3}^{-},$ and (e) $\mathrm{GaH}_{3}$.

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Problem 74

Predict the shapes of (a) $\mathrm{SF}_{3}^{+}$, (b) $\mathrm{GeF}_{4}$ (c) $\mathrm{SO}_{4}^{2-}$, (d) $\mathrm{O}_{3},$ and (e) $\mathrm{N}_{2} \mathrm{O}$.

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Problem 75

Predict the shapes of (a) $\mathrm{FCl}_{2}^{+},$ (b) $\mathrm{AsF}_{5},$ (c) $\mathrm{AsF}_{3}$, (d) $\mathrm{SbH}_{3}$, and (e) $\mathrm{SeO}_{2}$.

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Problem 76

Predict the shapes of (a) $\mathrm{TeF}_{4}$,
(b) $\mathrm{SbCl}_{6}$
(c) $\mathrm{NO}_{2},$
(d) $\mathrm{PCl}_{4}$, and
(e) $\mathrm{PO}_{4}^{3-}$.

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Problem 77

Predict the shapes of (a) $\mathrm{IO}_{4}^{-},(\mathbf{b}) \mathrm{IF}_{4}^{-},(\mathbf{c}) \mathrm{TeF}_{6},(\mathbf{d}) \mathrm{SiO}_{4}$
and (e) $\mathrm{ICl}_{2}$.

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Problem 78

Predict the shapes of (a) $\mathrm{CS}_{2},$ (b) $\mathrm{BrF}_{4}^{-},$ (c) $\mathrm{ICl}_{3}$, (d) $\mathrm{ClO}_{3}^{-},$ and (e) $\mathrm{SeO}_{3}$.

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Problem 79

Which of the following has a shape described by the figure below: (a) $\mathrm{IO}_{4}^{-},(\mathbf{b}) \mathrm{ICl}_{4}^{-},(\mathbf{c}) \mathrm{Sn} \mathrm{Cl}_{4},$ or $(\mathbf{d}) \mathrm{BrF}_{4}^{+} ?$

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Problem 80

Which of the following has a shape described by the figure below: (a) $\mathrm{BrF}_{3},$ (b) $\mathrm{PF}_{3},$ (c) $\mathrm{NO}_{3}^{-}$, or (d) $\mathrm{SCl}_{3}^{-}$ ?

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Problem 81

Ethene, also called ethylene, is a gas used to ripen tomatoes artificially. It has the Lewis structure:
What would you expect the $\mathrm{H}-\mathrm{C}-\mathrm{H}$ and $\mathrm{H}-\mathrm{C}=\mathrm{C}$
bond angles to be in this molecule? (Caution: Don't be fooled by the way the structure is drawn here.)

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Problem 83

Ethyne, more commonly called acetylene, is a gas used in welding torches. It has the Lewis structure $\mathrm{H}-\mathrm{C} \equiv \mathrm{C}-\mathrm{H}$. What would you expect the $\mathrm{H}-\mathrm{C}-\mathrm{C}$ bond angle to be in this molecule?

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Problem 83

Predict the bond angle for each of the following molecules:
(a) $\mathrm{Cl}_{2} \mathrm{O}$
(b) $\mathrm{H}_{2} \mathrm{O}$
(c) $\mathrm{SO}_{2}$
(d) $\mathrm{HOCl}$
(e) $\mathrm{SnF}_{2}$.

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Problem 84

Predict the bond angle for each of the following ions:
(a) $\mathrm{I}_{3}^{-},$ (b) $\mathrm{PH}_{2}^{-}$,
(c) $\mathrm{OCN}^{-},$
(d) $\mathrm{PO}_{4}^{3-}$,
(e) $\mathrm{NH}_{2}^{-}$.

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Problem 85

Which of the following molecules would be expected to be polar?
(a) $\mathrm{HBr}$
(b) $\mathrm{POCl}_{3}$,
(c) $\mathrm{CH}_{2} \mathrm{O}$
(d) $\mathrm{SnCl}_{4}$,
(e) $\mathrm{SbCl}_{5}$.

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Problem 86

Which of the following molecules would be expected to be polar? (a) $\mathrm{PBr}_{3},$ (b) $\mathrm{SO}_{3},$ (c) $\mathrm{AsCl}_{3},$ (d) $\mathrm{ClF}_{3},$ (e) $\mathrm{BCl}_{3}$.

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Problem 87

Which of the following molecules or ions would be expected to have a net dipole moment?
(a) CINO, (b) $\mathrm{XeF}^{+}$ (c) SeBr, (d) $\mathrm{NO}$ (e) $\mathrm{NO}_{2}$.

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Problem 88

Which of the following molecules or ions would be expected to have a net dipole moment?
(a) $\mathrm{H}_{2} \mathrm{~S},(\mathbf{b}) \mathrm{BeH}_{2},$
(c) $\mathrm{SCN}^{-}$,
(d) $\mathrm{CN}^{-}$,
(e) $\mathrm{BrCl}_{3}$

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Problem 89

Explain why $\mathrm{SF}_{6}$ is nonpolar, but $\mathrm{SF}_{5} \mathrm{Br}$ is polar.

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Problem 90

Explain why $\mathrm{CH}_{3} \mathrm{Cl}$ is polar, but $\mathrm{CCl}_{4}$ is not.

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Problem 91

Use sketches of orbitals to show how VB theory explains the bonding in the $\mathrm{Cl}_{2}$ molecule. Illustrate with appropriate orbital diagrams as well.

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Problem 92

Hydrogen selenide is one of nature's most foul-smelling substances. Molecules of $\mathrm{H}_{2} \mathrm{Se}$ have $\mathrm{H}-\mathrm{Se}-\mathrm{H}$ bond angles very close to $90^{\circ} .$ How would $\mathrm{VB}$ theory explain the bonding in $\mathrm{H}_{2}$ Se? Use sketches of orbitals to show how the bonds are formed. Illustrate with appropriate orbital diagrams as well.

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Problem 93

Use orbital diagrams to explain how the beryllium chloride molecule is formed. What kind of hybrid orbitals does beryllium use in this molecule?

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Problem 94

Use orbital diagrams to describe the bonding in tin tetrachloride? What kind of hybrid orbitals does beryllium use in this molecule?

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Problem 95

Use orbital diagrams to describe the bonding in antimony pentachloride, a substance used to add chlorine to carbon compounds. Be sure to indicate hybrid orbital formation.

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Problem 96

Describe the bonding in tellurium hexafluoride, a toxic gas with an extremely unpleasant smell. Indicate the hybrid orbitals used by the tellurium.

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Problem 97

Draw Lewis structures for the following and use the geometry predicted by the VSEPR model to determine what kind of hybrid orbitals the central atom uses in bond formation: (a) $\mathrm{ClO}_{3}^{-},(\mathbf{b}) \mathrm{SO}_{3},$ and $(\mathbf{c}) \mathrm{OF}_{2}$.

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Problem 98

Draw Lewis structures for the following and use the geometry predicted by the VSEPR model to determine what kind of hybrid orbitals the central atom uses in bond formation: (a) $\mathrm{SbCl}_{6}^{-},$ (b) $\mathrm{PF}_{3}$, and (c) $\mathrm{XeF}_{4}$.

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Problem 99

Use the VSEPR model to help you describe the bonding in the following molecules according to VB theory: (a) arsenic trichloride and (b) chlorine trifluoride. Use orbital diagrams for the central atom to show how hybridization occurs.

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Problem 100

Use the VSEPR model to help you describe the bonding in the following molecules according to VB theory: (a) antimony trichloride and (b) selenium dichloride. Use orbital diagrams for the central atom to show how hybridization occurs.

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Problem 101

Use orbital diagrams to show that the bonding in $\mathrm{SbF}_{6}$ involves the formation of a coordinate covalent bond.

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Problem 102

What kind of hybrid orbitals are used by tin in $\mathrm{SnCl}_{6}^{2-} ?$ Draw the orbital diagram for $\mathrm{Sn}$ in $\mathrm{SnCl}_{6}^{2-}$. What is the geometry of $\mathrm{SnCl}_{6}^{2-}$ ?

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Problem 103

A nitrogen atom can undergo sp $^{2}$ hybridization when it becomes part of a carbon-nitrogen double bond, as in $\mathrm{H}_{2} \mathrm{C}=\mathrm{NH}$
(a) Using a sketch, show the electron configuration of $s p^{2}$ hybridized nitrogen just before the overlapping occurs to make this double bond.
(b) Using sketches (and the analogy to the double bond in $\left.\mathrm{C}_{2} \mathrm{H}_{4}\right),$ describe the two bonds of the carbonnitrogen double bond.
(c) Describe the geometry of $\mathrm{H}_{2} \mathrm{C}=\mathrm{NH}$ (use a sketch to show all the expected bond angles.)

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Problem 104

A nitrogen atom can undergo sp hybridization and then become joined to carbon by a triple bond.
(a) How many sigma and pi bonds make up the triple bond?
(b) Draw the orbital diagram for the sp hybridization as it would look before any bonds are formed.
(c) Draw sketches to show where the electron density of each bond in the triple bond is located.
(d) What do you expect the bond angle for the HCN molecule to be?

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Problem 105

Tetrachloroethylene, a common dry-cleaning solvent, has the formula $\mathrm{C}_{2} \mathrm{Cl}_{4}$. Its structure is
Use the VSEPR and VB theories to describe the bonding in this molecule. What are the expected bond angles in the molecule?

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Problem 106

Phosgene, $\mathrm{COCl}_{2}$, was used as a war gas during World War I. It reacts with moisture in the lungs of its victims to form $\mathrm{CO}_{2}$ and gaseous $\mathrm{HCl}$, which cause the lungs to fill with fluid. Phosgene is a simple molecule having the structure
Describe the bonding in this molecule using VSEPR and VB theory.

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Problem 107

What kind of hybrid orbitals do the numbered atoms use in the following molecule?

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Problem 108

What kind of hybrid orbitals do the numbered atoms use in the following molecule?

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Problem 109

What kinds of bonds $(\sigma,$ and $\pi)$ are found in the numbered bonds in the following molecule?

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Problem 110

What kinds of bonds $(\sigma, \pi)$ are found in the numbered bonds in the following molecule?

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Problem 111

Construct the molecular orbital diagram for $\mathrm{O}_{2} .$ What is the net bond order in $\mathrm{O}_{2} ?$

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Problem 112

Construct the molecular orbital diagram for $\mathrm{N}_{2} .$ What is the new bond order in $\mathrm{N}_{2}$ ?

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Problem 113

Use the MO energy diagram to predict (a) the bond orders for each molecule or ion, (b) which one has the longer bond length, and (c) which in each pair has the greater bond energy: (i) $\mathrm{O}_{2}$ or $\mathrm{O}_{2}^{+},($ ii $) \mathrm{O}_{2}$ or $\mathrm{O}^{-}$.

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Problem 114

Use the MO energy diagram to predict (a) the bond orders for each molecule or ion, (b) which one has the longer bond length, and $(\mathbf{c})$ which in each pair has the
(ii) $\mathrm{N}_{2}$ or $\mathrm{N}_{2}{ }^{+}$.
greater bond energy:
(i) $\mathrm{C}_{2}$ or $\mathrm{C}_{2}^{+}$

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Problem 115

Assume that in the $\mathrm{NO}$ molecule the molecular orbital energy level sequence is similar to that for $\mathrm{O}_{2}$. What happens to the NO bond length when an electron is removed from $\mathrm{NO}$ to give $\mathrm{NO}^{+} ?$ How would the bond energy of NO compare to that of $\mathrm{NO}^{+}$ ?

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Problem 116

Assume that in the $\mathrm{NO}$ molecule the molecular orbital energy level sequence is similar to that for $\mathrm{O}_{2}$. What happens to the NO bond length when an electron is added to $\mathrm{NO}$ to give $\mathrm{NO}^{-} ?$ How would the bond energy of $\mathrm{NO}$ compare to that of $\mathrm{NO}^{-} ?$

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Problem 117

Which of the following molecules or ions are paramagnetic? (a) $\mathrm{O}_{2}^{+},(\mathbf{b}) \mathrm{O}_{2},(\mathbf{c}) \mathrm{O}_{2}^{-},(\mathbf{d}) \mathrm{NO},$ (e) $\mathrm{N}_{2}$

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Problem 118

Which of the following molecules or ions are paramagnetic? (a) $\mathrm{B}_{2},(\mathbf{b}) \mathrm{C}_{2},(\mathbf{c}) \mathrm{C}_{2}^{-},(\mathbf{d}) \mathrm{C}_{2}^{2-},(\mathrm{e}) \mathrm{F}_{2}$.

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Problem 119

Construct the MO energy level diagram for the OH molecule assuming it is similar to that for HF. How many electrons are in (a) bonding MOs and (b) nonbonding MOs? What is the net bond order in the molecule?

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Problem 120

If boron and nitrogen were to form a molecule with the formula $\mathrm{BN}$, what would its $\mathrm{MO}$ energy level diagram look like, given that the energies of the $2 p$ orbitals of nitrogen are lower than those of boron? If Figure $9.41 a$ applies, would the molecule be paramagnetic or diamagnetic? What is the net bond order in the molecule?

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Problem 121

Formaldehyde has the Lewis structure
What would you predict its shape to be?

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Problem 122

The molecule $X \mathrm{Cl}_{3}$ is pyramidal. In which group in the periodic table is element $X$ found? If the molecule were planar triangular, in which group would $X$ be found? If the molecule were T-shaped, in which group would $X$ be found? Why is it unlikely that element $X$ is in Group 6 A?

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Problem 123

Antimony forms a compound with hydrogen that is called stibine. Its formula is $\mathrm{SbH}_{3}$ and the $\mathrm{H}-\mathrm{Sb}-\mathrm{H}$ bond angles are $91.3^{\circ} .$ Which kinds of orbitals does $S b$ most likely use to form the $\mathrm{Sb}-\mathrm{H}$ bonds: pure $p$ orbitals or hybrid orbitals? Explain your reasoning.

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Problem 124

Describe the changes in molecular geometry and hybridization that take place during the following reactions:
(a) $\mathrm{BF}_{3}+\mathrm{F}^{-} \longrightarrow \mathrm{BF}_{4}^{-}$
(b) $\mathrm{PCl}_{5}+\mathrm{Cl}^{-} \longrightarrow \mathrm{PCl}_{4}^{-}$
(c) $\mathrm{ICl}_{3}+\mathrm{Cl}^{-} \longrightarrow \mathrm{ICl}_{4}^{-}$
(d) $\mathrm{PCl}_{3}+\mathrm{Cl}_{2} \longrightarrow \mathrm{PCl}_{5}$
(e) $\mathrm{C}_{2} \mathrm{H}_{2}+\mathrm{H}_{2} \longrightarrow \mathrm{C}_{2} \mathrm{H}_{4}$

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Problem 125

Which one of the following five diagrams best represents the structure of $\mathrm{BrCl}_{4}^{+} ?$
a.
b.
c.
d.
e.

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Problem 126

Cyclopropane is a triangular molecule with $\mathrm{C}-\mathrm{C}-\mathrm{C}$ bond angles of $60^{\circ} .$ Explain why the $\sigma$ bonds joining carbon atoms in cyclopropane are weaker than the carboncarbon $\sigma$ bonds in the noncyclic propane.

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Problem 127

Phosphorus trifluoride, $\mathrm{PF}_{3}$, has $\mathrm{F}-\mathrm{P}-\mathrm{F}$ bond angles of $97.8^{\circ} .$ (a) How would VB theory use hybrid orbitals to explain these data? (b) How would VB theory use unhybridized orbitals to account for these data? (c) Do either of these models work very well?

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Problem 128

A six-membered ring of carbons can hold a double bond but not a triple bond. Explain.

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Problem 129

The more electronegative are the atoms bonded to the central atom, the less are the repulsions between the electron pairs in the bonds. On the basis of this statement, predict the most probable structure for the molecule $\mathrm{PCl}_{3} \mathrm{~F}_{2} .$ Do we expect the molecule to be polar or nonpolar?

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Problem 130

$A$ lone pair of electrons in the valence shell of an atom has a larger effective volume than a bonding electron pair. Lone pairs therefore repel other electron pairs more strongly than do bonding pairs. On the basis of these statements, describe how the bond angles in $\mathrm{TeF}_{4}$ and $\mathrm{BrF}_{5}$ deviate from those found in a trigonal bipyramid and an octahedron, respectively. Sketch the molecular shapes of $\mathrm{TeF}_{4}$ and $\mathrm{BrF}_{5}$ and indicate these deviations on your drawing.

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Problem 131

The two electron pairs in a double bond repel other electron pairs more than the single pair of electrons in a single bond. On the basis of this statement, which bond angles should be larger in $\mathrm{SO}_{2} \mathrm{Cl}_{2},$ the $\mathrm{O}-\mathrm{S}-\mathrm{O}$ bond angles or the $\mathrm{Cl}-\mathrm{S}-\mathrm{Cl}$ bond angles? In the molecule, sulfur is bonded to two oxygen atoms and two chlorine atoms. (Hint: Assign formal charges and work with the best Lewis structure for the molecule.).

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Problem 132

In a certain molecule, a $p$ orbital overlaps with a $d$ orbital as shown.
The algebraic signs of the lobes of the $d$ -orbital wave function are also indicated in the drawing. Which kind of bond is formed, $\sigma$ or $\pi$ ? Explain your choice. Repeat the drawing twice on a separate sheet of paper. In one of them, indicate the signs of the lobes of the $p$ -orbital wave function that would lead to a bonding MO. In the other, indicate the signs of the lobes of the $p$ -orbital wave function that would lead to an antibonding MO.

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Numerade Educator

Problem 133

If we assign the internuclear axis in a diatomic molecule to be the $z$ axis, what kind of $p$ orbital $\left(p_{x}, p_{y},\right.$ or $\left.p_{z}\right)$ on one atom would have to overlap with a $d_{x z}$ orbital on the other atom to give a $\pi$ bond?

David Collins

Numerade Educator

Problem 134

The peroxynitrite ion, $\mathrm{OONO}^{-},$ is a potent toxin formed in cells affected by diseases such as diabetes and atherosclerosis. Peroxynitrite ion can oxidize and destroy biomolecules crucial for the survival of the cell. (a) Give the $\mathrm{O}-\mathrm{O}-\mathrm{N}$ and $\mathrm{O}-\mathrm{N}-\mathrm{O}$ bond angles in the peroxynitrite ion. (b) What is the hybridization of the $\mathrm{N}$ atom in the peroxynitrite ion? (c) Suggest why the peroxynitrite ion is expected to be much less stable than the nitrate ion, $\mathrm{NO}_{3}^{-}$.

David Collins

Numerade Educator

Problem 135

An ammonia molecule, $\mathrm{NH}_{3}$, is very polar, whereas $\mathrm{NF}_{3}$ is almost nonpolar. Use this observation along with the valence bond description of bonding in these molecules to justify the following statement: Lone pairs in bybrid or- bitals contribute to the overall dipole moment of a molecule.

David Collins

Numerade Educator

Problem 136

There exists a hydrocarbon called butadiene, which has the molecular formula $\mathrm{C}_{4} \mathrm{H}_{6}$ and the structure The $\mathrm{C}=\mathrm{C}$ bond lengths are $134 \mathrm{pm}$ (about what is expected for a carbon-carbon double bond), but the $\mathrm{C}-\mathrm{C}$ bond length in this molecule is $147 \mathrm{pm}$, which is shorter than a normal $\mathrm{C}-\mathrm{C}$ single bond. The molecule is planar (i.e., all the atoms lie in the same plane).
(a) What kind of hybrid orbitals do the carbon atoms use in this molecule to form the $\mathrm{C}-\mathrm{C}$ bonds?
(b) Between which pairs of carbon atoms do we expect to find sideways overlap of $p$ orbitals (i.e., $\pi$ -type $p-p$ overlap)?
(c) Based on your answer to parts (a) and (b), explain why the center carbon-carbon bond is shorter than a carbon-carbon single bond.

David Collins

Numerade Educator

Problem 137

A $0.244 \mathrm{~g}$ sample of a compound of phosphorus and bromine, when dissolved in water, reacted to give a solution containing phosphorus acid and bromide ion. Addition of excess $\mathrm{AgNO}_{3}$ solution to the mixture led to precipitation of AgBr. When the precipitate of $\mathrm{AgBr}$ was collected and dried, it weighed $0.508 \mathrm{~g}$. Determine the chemical formula of the phosphorus-bromine compound and predict whether its molecules are polar or nonpolar.

David Collins

Numerade Educator

Problem 138

Five basic molecular shapes were described for simple molecular structures containing a central atom bonded to various numbers of surrounding atoms. Can you suggest additional possible structures? Provide arguments about the likelihood that these other structures might actually exist.

David Collins

Numerade Educator

Problem 139

Compare and contrast the concepts of delocalization and resonance.

David Collins

Numerade Educator

Problem 140

Why doesn't a carbon-carbon quadruple bond exist?

David Collins

Numerade Educator

Problem 141

What might the structure of the iodine heptafluoride molecule be? If you can think of more than one possible structure, which is likely to be of lowest energy based on the VSEPR model?

David Collins

Numerade Educator

Problem 142

The $\mathrm{F}-\mathrm{F}$ bond in $\mathrm{F}_{2}$ is weaker than the $\mathrm{Cl}-\mathrm{Cl}$ bond in $\mathrm{Cl}_{2}$. How might the lone pairs on the atoms in the molecules be responsible for this?

David Collins

Numerade Educator

Problem 143

Molecular orbital theory predicts the existence of antibonding molecular orbitals. How do antibonding electrons affect the stability in a molecule?

David Collins

Numerade Educator

Problem 144

The structure of the diborane molecule, $\mathrm{B}_{2} \mathrm{H}_{6}$, is sometimes drawn as
There are not enough valence electrons in the molecule to form eight single bonds, which is what the structure implies. Assuming that the boron atoms use $s p^{3}$ hybrid orbitals, suggest a way that hydrogen $1 s$ orbitals can be involved in forming delocalized molecular orbitals that bridge the two boron atoms. Use diagrams to illustrate your answer. What would be the average bond order in the bridging bonds?

Freddie Montague

Freddie Montague

Numerade Educator