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CHAPTER 10
CHEMICAL BONDING II
10.8 Predict the geometries of the following species: (a) AlCl3, (b) ZnCl2 , (c) ZnCl4210.10 Predict the geometries of the following ions:
(a) NH4+, (b) NH-2 , (c) CO32- (d) ICl-2 , (e) ICl-4 , (f) AIH-4 , (g) SnCl-5 , (h) H3O+ , (i) BeF4210.12 Which of the following species are tetrahedral? SiCl4 , SeF4 , XeF4, CI4 , CdCl2-4
10.18 The dipole moments of the hydrogen halides decrease from HF to HI (see Table 10.3). Explain
this trend.
10.20 Does the molecule OCS have a higher or lower dipole moment than CS2?
10.21 Which of the following molecules has a higher dipole moment ?
Br
H
C=C
H
Br
Br
H
C=C
Br
H
(a)
(b)
10.22 Arrange the following compounds in order of increasing dipole moment:
Cl
Cl
Cl
Cl
Cl Cl
Cl
Cl
Cl
Cl
10.32 What is the hybridization of Si in SiH4 and in H3Si−SiH3 ?
10.34 Consider the reaction
BF3 + NH3 → F3B − NH3
10.36 What are the hybrid orbitals of the carbon atoms in the following molecules ?
(b) H3C − CH = CH2
(a) H3C − CH3
(c) H3C − C ≡ C − CH2OH
(d) CH3CH = O
(e) CH3COOH
10.38 What is the hybridization state of the central N atom in the azide ion, N-3 ? (Arrangement of
atoms: NNN.)
10.40 Describe the hybridization of phosphorus in PF5,
10.41 How many sigma bonds and pi bonds are there in each of the following molecules ?
H
H
H
Cl
Cl C Cl
C=C
H3C C C C C H
H
H
H
H
(a)
(b)
(c)
2
10.42 How many pi bonds and sigma bonds are there in the tetracyanoethylene molecule?
N C
N C
C C
C N
C N
10.48 The formation of H2 from two H atoms is an energetically favorable process. Yet statistically
there is less than a 100 percent chance that any two H atoms will undergo the reaction. Apart
from energy considerations, how would you account for this observation based on the electron
spins in the two H atoms?
10.50 Arrange the following species in order of increasing stability: Li2, Li+2, Li-2 . Justify your choice
with a molecular orbital energy level diagram.
10.52 Which of these species has a longer bond, B2 or B+2 ? Explain in terms of molecular orbital
theory.
10.54 Compare the Lewis and molecular orbital treatments of the oxygen molecule.
10.56 Compare the relative stability of the following species and indicate their magnetic properties
(that is, diamagnetic or paramagnetic): O2, O+2, O-2. (superoxide ion), O2-2 (peroxide ion).
10.58 A single bond is almost always a sigma bond, and a double bond is almost always made up of
a sigma bond and a pi bond. There are very few exceptions to this rule. Show that the B2 and
C2 molecules are examples of the exceptions.
10.62 Explain why the symbol on the left is a better representation of benzene molecules than that on
the right.
10.64 Nitryl fluoride (FNO2) is very reactive chemically. The fluorine and oxygen atoms are bonded
to the nitrogen atom. (a) Write a Lewis structure for FNO2 , (b) Indicate the hybridization of the
nitrogen atom. (c) Describe the bonding in terms of molecular orbital theory. Where would you
expect delocalized molecular orbitals to form?
10.66 What is the state of hybridization of the central O atom in O3 ? Describe the bonding in O3 in
terms of delocalized molecular orbitals.
10.68 Draw the Lewis structure of mercury (II) bromide. Is this molecule linear or bent? How would
you establish its geometry?
10.69 Sketch the bond moments and resultant dipole moments for the following molecules: H2O,
PCl3, XeF4 , PCl5, SF6.
10.70 Although both carbon and silicon are in Group 4A, very few Si = Si bonds are known. Account
for the instability of silicon – to – silicon double bonds in general. (Hint: Compare the atomic
radii of C and Si in Figure 8.5. What effect would the larger size have on pi bond formation?)
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10.72 Antimony pentafluoride, SbF5, reacts with XeF4 and XeF6 to form ionic compounds, XeF3+SbF-6
and XeF5+SbF6-. Describe the geometries of the cations and anion in these two compounds.
10.74 Predict the bond angles for the following molecules: (a) BeCl2 , (b) BCl3, (c) CCl4, (d) CH3Cl,
(e) Hg2Cl2 (arrangement of atoms: CIHgHgCl), (f) SnCl2, (g) H2O2, (h) SnH4.
10.78Which of the following molecules are linear? ICl-2 , IF+2 , OF2 , Snl2 , CdBr2
10.80 The N2F2 molecule exist in either of the following two forms :
F F
F
N=N
N=N
F
10.82 The compound 1, 2-dichloroethane (C2H4Cl2) is nonpolar, while cis- dichloroethane (C2H2Cl2)
has a dipole moment:
Cl Cl
H C C H
H H
Cl
H
C=C
Cl
H
1,2-dichloroethane
cis-dichloroethylene
The reason for the difference is that groups connected by a single bond can rotate with
respect to each other, but no rotation occurs when a double bond connects the groups. On
the basis of bonding considerations, explain why rotation occurs in 1,2-dichloroethane but not
in cis-dichloroethylene.
10.84 So – called greenhouse gases, which contribute to global warming, have a dipole moment or
can be bent or distorted into shapes that have a dipole moment. Which of the following gases
are greenhouse gases ? N2, O2, O3, CO, CO2, NO2, N2O, CH4, CFCl3
10.86 3′-azido-3′-deoxythymidine, commonly known as AZT, is one of the drugs used to treat
acquired immune deficiency syndrome (AIDS). What are the hybridization states of the C and
N atoms in this molecule?
O
C
H
N
C
C
O
HO
C H2
C H
H
N
O
H C
C
C
N
H
N
N
C H3
C
H
H
4
10.87 The following molecules (AX4Y2) all have octahedral geometry. Group the molecules that are
equivalent to each other.
Y
X
X
X
Y
A
Y
X
X
X
X
A
Y
(a)
X
(b)
X
X
A
Y
X
X
X
X
(c)
A
Y
X
Y
Y
X
(d)
10.88 The compounds carbon tetrachloride (CCl4) and silicon tetrachloride (SiCl4) are similar in
geometry and hybridization. However, CCl4 does not react with water but SiCl4 does. Explain the
difference in their chemical reactivties. (Hint: The first step of the reaction is believed to be the
addition of a water molecule to the Si atom in SiCl4.)
10.90 What are the hybridization states of the C and N atoms in this molecule?
NH 2
H
C
N
C
C
O
C
N
H
H
10.92 Referring to the Chemistry in Action on p. 382, answer the following questions: (a) If you wanted
to cook a roast (beef or lamb), would you use a microwave oven or a conventional oven? (b)
Radar is a means of locating an object by measuring the time for the echo of a microwave from
the object to return to the source and the direction from which it returns. Would radar work if
oxygen, nitrogen, and carbon dioxide were polar molecules? (c) In early tests of radar at the
English Channel during World War II, the results were inconclusive even though there was no
equipment malfunction. Why? (Hint: The weather is often foggy in that region.)
10.94 Referring to Table 9.4, explain why the bond energy for Cl2 is greater than that for F2. (Hint: The
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bond lengths of F2 and Cl2 are 142 pm and 199 pm, respectively.)
10.95 The ionic character of the bond in a diatomic molecule can be estimated by the formula
µ
x 100%
ed
where µ is the experimentally measured dipole moment (in C m), e the electronic charge, and
d the bond length in meters. (The quantity ed is the hypothetical dipole moment for the case in
which the transfer of an electron from the less electronegative to the more electronegative atom
is complete.) Given that the dipole moment and bond length of HF are 1.92 D and 91.7 pm,
respectively, calculate the percent ionic character of the molecule.
11.8 If you lived in Alaska, which of the following natural gases would you keep in an outdoor storage
tank in winter? Explain why. Methane (CH4), propane (C3H8), or butane (C4H10)
11.10 List the types of intermolecular forces that exist between molecules (or basic units) in each of the
following species: (a) benzene (C6H6), (b) CH3Cl, (c) PF3, (d) NaCl, (e) CS2.
11.12 Which of the following species are capable of hydrogen-bonding among themselves? (a) C2H6 ,
(b) HI, (c) KF, (d) BeH2, (e) CH3COOH
11.14 Diethyl ether has a boiling point of 34.5°C, and 1-butanol has a boiling point of 117°C:
H
H
H
C
C
H
H
O
H
H
C
C
H
H
H
H
diethyl ether
H
H
H
H
C
C
C
C
H
H
H
H
H
1-butanol
Boht of these compounds have the same numbers and types of atoms. Explain the difference in
their boiling points.
11.16 Which substance in each of the following pairs would you expect to have the higher boiling
point? Explain why. (a) Ne or Xe, (b) CO2 or CS2, (c) CH4 or Cl2, (d) F2 or LiF, (e) NH3 or PH3
11.18 What kind of attractive forces must be overcome in order to (a) melt ice, (b) boil molecular
bromine, (c) melt solid iodine, and (d) dissociate F2 into F atoms?
11.20 Explain the difference in the melting points of the following compounds:
NO2
OH
NO2
OH
m.p. 45°C
m.p. 115°C
(Hint: Only one of the two can form intramolecular hydrogen bonds.)