Chemistry

Raymond Chang, Jason Overby

Chapter 9

Chemical Bonding I: Basic Concepts - all with Video Answers

Educators

Chapter Questions

Problem 1

What is a Lewis dot symbol? To what elements does the symbol mainly apply?

JO

Joseph Ochterski

Numerade Educator

Problem 2

Use the second member of each group from Group 1A to Group 7 A to show that the number of valence electrons on an atom of the element is the same as its group number.

Cameron Oden

Numerade Educator

Problem 3

Without referring to Figure $9.1,$ write Lewis dot symbols for atoms of the following elements:
(a) $\mathrm{Be},(\mathrm{b}) \mathrm{K},(\mathrm{c}) \mathrm{Ca},(\mathrm{d}) \mathrm{Ga},(\mathrm{e}) \mathrm{O},(\mathrm{f}) \mathrm{Br},(\mathrm{g}) \mathrm{N},(\mathrm{h})$
I, (i) As, (j) F.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 4

Write Lewis dot symbols for the following ions: (a) $\mathrm{Li}^{+},(\mathrm{b}) \mathrm{Cl}^{-},(\mathrm{c}) \mathrm{S}^{2-},(\mathrm{d}) \mathrm{Sr}^{2+},(\mathrm{e}) \mathrm{N}^{3-}$

Freddie Montague

Freddie Montague

Numerade Educator

Problem 5

Write Lewis dot symbols for the following atoms
(g) $\mathrm{Na},$ (h) $\mathrm{Na}^{+}$,
(i) $\mathrm{Mg},(\mathrm{j}) \mathrm{Mg}^{2+},(\mathrm{k}) \mathrm{Al},$
(1) $\mathrm{Al}^{3+}$
$(\mathrm{m}) \mathrm{Pb},(\mathrm{n}) \mathrm{Pb}^{2+}$

Anand Jangid

Numerade Educator

Problem 6

Explain what an ionic bond is.

Cameron Oden

Numerade Educator

Problem 7

Explain how ionization energy and electron affinity determine whether atoms of elements will combine to form ionic compounds.

Dr. Satish Ingale

Dr. Satish Ingale

Numerade Educator

Problem 8

Name five metals and five nonmetals that are very likely to form ionic compounds. Write formulas for compounds that might result from the combination of these metals and nonmetals. Name these compounds.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 9

Name one ionic compound that contains only nonmetallic elements.

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator

Problem 10

Name one ionic compound that contains a polyatomic cation and a polyatomic anion (see Table 2.3 ).

Cameron Oden

Numerade Educator

Problem 11

Explain why ions with charges greater than 3 are seldom found in ionic compounds.

Iryna Ivaniuk

Numerade Educator

Problem 12

The term "molar mass" was introduced in Chapter 3 . What is the advantage of using the term "molar mass" when we discuss ionic compounds?

Cameron Oden

Numerade Educator

Problem 13

In which of the following states would $\mathrm{NaCl}$ be electrically conducting:
(a) solid, (b) molten (that is, melted), (c) dissolved in water? Explain your answers.

Iryna Ivaniuk

Numerade Educator

Problem 14

Beryllium forms a compound with chlorine that has the empirical formula $\mathrm{BeCl}_{2}$. How would you determine whether it is an ionic compound? (The compound is not soluble in water.)

Freddie Montague

Freddie Montague

Numerade Educator

Problem 15

An ionic bond is formed between a cation $\mathrm{A}^{+}$ and an anion $\mathrm{B}^{-}$. How would the energy of the ionic bond [see Equation (9.2)$]$ be affected by the following changes? (a) doubling the radius of $\mathrm{A}^{+},$ (b) tripling the charge on $\mathrm{A}^{+},$ (c) doubling the charges on $\mathrm{A}^{+}$ and $\mathrm{B}^{-},$ (d) decreasing the radii of $\mathrm{A}^{+}$ and $\mathrm{B}^{-}$ to half their original values

Iryna Ivaniuk

Numerade Educator

Problem 16

Give the empirical formulas and names of the compounds formed from the following pairs of ions:
(a) $\mathrm{Rb}^{+}$ and $\mathrm{I}^{-},$ (b) $\mathrm{Cs}^{+}$ and $\mathrm{SO}_{4}^{2-},$ (c) $\mathrm{Sr}^{2+}$ and $\mathrm{N}^{3-}$
(d) $\mathrm{Al}^{3+}$ and $\mathrm{S}^{2-}$

Cameron Oden

Numerade Educator

Problem 17

Use Lewis dot symbols to show the transfer of electrons between the following atoms to form cations and anions: (a) $\mathrm{Na}$ and $\mathrm{F},(\mathrm{b}) \mathrm{K}$ and $\mathrm{S},$ (c) $\mathrm{Ba}$ and $\mathrm{O},$ (d) Al and N.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 18

Write the Lewis dot symbols of the reactants and products in the following reactions. (First balance the equations.)
(a) $\mathrm{Sr}+\mathrm{Se} \longrightarrow \mathrm{SrSe}$
(b) $\mathrm{Ca}+\mathrm{H}_{2} \longrightarrow \mathrm{CaH}_{2}$
(c) $\mathrm{Li}+\mathrm{N}_{2} \longrightarrow \mathrm{Li}_{3} \mathrm{~N}$
(d) $\mathrm{Al}+\mathrm{S} \longrightarrow \mathrm{Al}_{2} \mathrm{~S}_{3}$

Cameron Oden

Numerade Educator

Problem 19

For each of the following pairs of elements, state whether the binary compound they form is likely to be ionic or covalent. Write the empirical formula and name of the compound:
(a) I and $\mathrm{Cl}$, (b) $\mathrm{Mg}$ and $\mathrm{F}$.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 20

For each of the following pairs of elements, state whether the binary compound they form is likely to be ionic or covalent. Write the empirical formula and name of the compound:
(a) $\mathrm{B}$ and $\mathrm{F},$ (b) $\mathrm{K}$ and $\mathrm{Br}$

Freddie Montague

Freddie Montague

Numerade Educator

Problem 21

What is lattice energy and what role does it play in the stability of ionic compounds?

Iryna Ivaniuk

Numerade Educator

Problem 22

Explain how the lattice energy of an ionic compound such as $\mathrm{KCl}$ can be determined using the Born-Haber cycle. On what law is this procedure based?

Cameron Oden

Numerade Educator

Problem 23

Specify which compound in the following pairs of ionic compounds has the higher lattice energy:
(a) $\mathrm{KCl}$ or $\mathrm{MgO},$ (b) LiF or $\mathrm{LiBr}$,
(c) $\mathrm{Mg}_{3} \mathrm{~N}_{2}$ or
$\mathrm{NaCl} .$ Explain your choice.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 24

Compare the stability (in the solid state) of the following pairs of compounds:
(a) $\mathrm{LiF}$ and $\mathrm{LiF}_{2}$ (containing the $\mathrm{Li}^{2+}$ ion $),$ (b) $\mathrm{Cs}_{2} \mathrm{O}$ and $\mathrm{CsO}$ (containing the $\mathrm{O}^{-}$ ion), (c) $\mathrm{CaBr}_{2}$ and $\mathrm{CaBr}_{3}$ (containing the $\mathrm{Ca}^{3+}$ ion $)$

Anand Jangid

Numerade Educator

Problem 25

Use the Born-Haber cycle outlined in Section 9.3 for LiF to calculate the lattice energy of $\mathrm{NaCl}$. [The heat of sublimation of $\mathrm{Na}$ is $108 \mathrm{~kJ} / \mathrm{mol}$ and $\Delta H_{\mathrm{f}}^{\circ}(\mathrm{NaCl})=-411 \mathrm{~kJ} / \mathrm{mol} .$ Energy needed to dissociate $\frac{1}{2}$ mole of $\mathrm{Cl}_{2}$ into $\mathrm{Cl}$ atoms $\left.=121.4 \mathrm{~kJ} .\right]$

Iryna Ivaniuk

Numerade Educator

Problem 26

Calculate the lattice energy of calcium chloride given that the heat of sublimation of Ca is $121 \mathrm{~kJ} /$ $\mathrm{mol}$ and $\Delta H_{\mathrm{f}}^{\circ}\left(\mathrm{CaCl}_{2}\right)=-795 \mathrm{~kJ} / \mathrm{mol} .$ (See Tables 8.2 and 8.3 for other data.)

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 27

What is Lewis's contribution to our understanding of the covalent bond?

Iryna Ivaniuk

Numerade Educator

Problem 28

Use an example to illustrate each of the following terms: lone pairs, Lewis structure, the octet rule, bond length.

Cameron Oden

Numerade Educator

Problem 29

What is the difference between a Lewis dot symbol and a Lewis structure?

Iryna Ivaniuk

Numerade Educator

Problem 30

How many lone pairs are on the underlined atoms in these compounds? $\mathrm{HBr}, \mathrm{H}_{2} \mathrm{~S}, \underline{\mathrm{C}} \mathrm{H}_{4}$

Freddie Montague

Freddie Montague

Numerade Educator

Problem 31

Compare single, double, and triple bonds in a molecule, and give an example of each. For the same bonding atoms, how does the bond length change from single bond to triple bond?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 32

Compare the properties of ionic compounds and covalent compounds.

Cameron Oden

Numerade Educator

Problem 33

Define electronegativity, and explain the difference between electronegativity and electron affinity. Describe in general how the electronegativities of the elements change according to position in the periodic table.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 34

What is a polar covalent bond? Name two compounds that contain one or more polar covalent bonds.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 35

List the following bonds in order of increasing ionic character: the lithium-to-fluorine bond in LiF, the potassium-to-oxygen bond in $\mathrm{K}_{2} \mathrm{O},$ the nitrogen-tonitrogen bond in $\mathrm{N}_{2}$, the sulfur-to-oxygen bond in $\mathrm{SO}_{2},$ the chlorine-to-fluorine bond in $\mathrm{ClF}_{3}$.

Sima Sarker

Numerade Educator

Problem 36

Arrange the following bonds in order of increasing ionic character: carbon to hydrogen, fluorine to hydrogen, bromine to hydrogen, sodium to chlorine, potassium to fluorine, lithium to chlorine.

Cameron Oden

Numerade Educator

Problem 37

Four atoms are arbitrarily labeled $D, \mathrm{E}, \mathrm{F},$ and $\mathrm{G} .$ Their electronegativities are as follows: $\mathrm{D}=3.8$, $\mathrm{E}=3.3, \mathrm{~F}=2.8,$ and $\mathrm{G}=1.3 .$ If the atoms of these elements form the molecules $\mathrm{DE}, \mathrm{DG}, \mathrm{EG},$ and $\mathrm{DF}$ how would you arrange these molecules in order of increasing covalent bond character?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 38

List the following bonds in order of increasing ionic character: cesium to fluorine, chlorine to chlorine, bromine to chlorine, silicon to carbon.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 39

Classify the following bonds as ionic, polar covalent, or covalent, and give your reasons:
(a) the CC bond in $\mathrm{H}_{3} \mathrm{CCH}_{3},$ (b) the KI bond in $\mathrm{KI}$, (c) the $\mathrm{NB}$ bond in $\mathrm{H}_{3} \mathrm{NBCl}_{3}$ (d) the CF bond in $\mathrm{CF}_{4}$.

Iryna Ivaniuk

Numerade Educator

Problem 40

Classify the following bonds as ionic, polar covalent, or covalent, and give your reasons: (a) the $\mathrm{SiSi}$ bond in $\mathrm{Cl}_{3} \mathrm{SiSiCl}_{3},$ (b) the $\mathrm{SiCl}$ bond in $\mathrm{Cl}_{3} \mathrm{SiSiCl}_{3}$, (c) the CaF bond in $\mathrm{CaF}_{2}$, (d) the $\mathrm{NH}$ bond in $\mathrm{NH}_{3}$.

Cameron Oden

Numerade Educator

Problem 41

Summarize the essential features of the Lewis octet rule.

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 42

The octet rule applies mainly to the second-period elements. Explain.

Lijeesh Krishnan

Lijeesh Krishnan

Numerade Educator

Problem 43

Write Lewis structures for the following molecules and ions: (a) $\mathrm{NCl}_{3},(\mathrm{~b}) \mathrm{OCS},(\mathrm{c}) \mathrm{H}_{2} \mathrm{O}_{2},(\mathrm{~d}) \mathrm{CH}_{3} \mathrm{COO}^{-}$
(e) $\mathrm{CN}^{-}$ (f) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{3}^{+}$

Iryna Ivaniuk

Numerade Educator

Problem 44

Write Lewis structures for the following molecules and ions:
(a) $\mathrm{OF}_{2},$ (b) $\mathrm{N}_{2} \mathrm{~F}_{2},$ (c) $\mathrm{Si}_{2} \mathrm{H}_{6},$ (d) $\mathrm{OH}^{-}$,
(e) $\mathrm{CH}_{2} \mathrm{ClCOO}^{-},$ (f) $\mathrm{CH}_{3} \mathrm{NH}_{3}^{+}$

Cameron Oden

Numerade Educator

Problem 45

Write Lewis structures for the following molecules:
(a) ICl, (b) $\mathrm{PH}_{3}$, (c) $\mathrm{P}_{4}$ (each $\mathrm{P}$ is bonded to three other $\mathrm{P}$ atoms
(d) $\mathrm{H}_{2} \mathrm{~S}$,
(e) $\mathrm{N}_{2} \mathrm{H}_{4}$,
(f) $\mathrm{HClO}_{3}$,
(g) $\mathrm{COBr}_{2}$ (C is bonded to $\mathrm{O}$ and $\mathrm{Br}$ atoms).

Iryna Ivaniuk

Numerade Educator

Problem 46

Write Lewis structures for the following molecules:
(a) $\mathrm{BrF}_{3},$ (b) $\mathrm{H}_{2} \mathrm{Te}$
(c) $\mathrm{NH}_{2} \mathrm{OH}$
(d) $\mathrm{POCl}_{3}$ (P is
bonded to $\mathrm{O}$ and $\mathrm{Cl}$ atoms $),$ (e) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~F}$,
(f) $\mathrm{NF}_{3}$,
(g) $\mathrm{CH}_{3} \mathrm{NH}_{2}$.

Anand Jangid

Numerade Educator

Problem 47

The following Lewis structures for (a) $\mathrm{HCN},$ (b) $\mathrm{C}_{2} \mathrm{H}_{2}$, (c) $\mathrm{SnO}_{2}$, (d) $\mathrm{BF}_{3}$, (e) $\mathrm{HOF}$, (f) $\mathrm{HCOF}$, and $(\mathrm{g}) \mathrm{NF}_{3}$ are incorrect. Explain what is wrong with each one and give a correct structure for the molecule. (Relative positions of atoms are shown correctly.)

Iryna Ivaniuk

Numerade Educator

Problem 48

The skeletal structure of acetic acid shown here is correct, but some of the bonds are wrong. (a) Identify the incorrect bonds and explain what is wrong with them. (b) Write the correct Lewis structure for acetic acid.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 49

Explain the concept of formal charge.

Pam Owens

Numerade Educator

Problem 50

Do formal charges represent actual separation of charges?

Nicole Krahulik

Nicole Krahulik

Numerade Educator

Problem 51

Write Lewis structures for the following ions:
(a) $\mathrm{NO}_{2}^{+},$ (b) $\mathrm{S}_{2}^{2-},$ (c) $\mathrm{BrF}_{2}^{+}$,
(d) $\mathrm{SCN}^{-}$. Show formal charges.

Anand Jangid

Numerade Educator

Problem 52

Write Lewis structures for the following ions:
(a) $\mathrm{O}_{2}^{2-},$ (b) $\mathrm{C}_{2}^{2-},$ (c) $\mathrm{NO}^{+}$,
(d) $\mathrm{NH}_{4}^{+}$. Show formal charges.

Cameron Oden

Numerade Educator

Problem 53

Define bond length, resonance, and resonance structure. What are the rules for writing resonance structures?

Iryna Ivaniuk

Numerade Educator

Problem 54

Is it possible to "trap" a resonance structure of a compound for study? Explain.

Cameron Oden

Numerade Educator

Problem 55

Write Lewis structures for the following species, including all resonance forms, and show formal charges:
(a) $\mathrm{HCO}_{2}^{-},$ (b) $\mathrm{CH}_{2} \mathrm{NO}_{2}^{-}$. Relative positions of the atoms are as follows:

Freddie Montague

Freddie Montague

Numerade Educator

Problem 56

Draw three resonance structures for the chlorate ion, $\mathrm{ClO}_{3}^{-}$. Show formal charges.

Cameron Oden

Numerade Educator

Problem 57

Write three resonance structures for hydrazoic acid, $\mathrm{HN}_{3}$. The atomic arrangement is HNNN. Show formal charges.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 58

Draw two resonance structures for diazomethane, $\mathrm{CH}_{2} \mathrm{~N}_{2} .$ Show formal charges. The skeletal structure of the molecule is

Freddie Montague

Freddie Montague

Numerade Educator

Problem 59

Draw three resonance structures for the molecule $\mathrm{N}_{2} \mathrm{O}_{3}$ (atomic arrangement is $\mathrm{ONNO}_{2}$ ). Show formal charges.

Iryna Ivaniuk

Numerade Educator

Problem 60

Draw three reasonable resonance structures for the $\mathrm{OCN}^{-}$ ion. Show formal charges.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 61

Why does the octet rule not hold for many compounds containing elements in the third period of the periodic table and beyond?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 62

Give three examples of compounds that do not satisfy the octet rule. Write a Lewis structure for each.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 63

Because fluorine has seven valence electrons $\left(2 s^{2} 2 p^{5}\right),$ seven covalent bonds in principle could form around the atom. Such a compound might be $\mathrm{FH}_{7}$ or $\mathrm{FCl}_{7}$. These compounds have never been prepared. Why?

Iryna Ivaniuk

Numerade Educator

Problem 64

What is a coordinate covalent bond? Is it different from a normal covalent bond?

Cameron Oden

Numerade Educator

Problem 65

The AlI $_{3}$ molecule has an incomplete octet around Al. Draw three resonance structures of the molecule in which the octet rule is satisfied for both the Al and the I atoms. Show formal charges.

Iryna Ivaniuk

Numerade Educator

Problem 66

In the vapor phase, beryllium chloride consists of discrete $\mathrm{BeCl}_{2}$ molecules. Is the octet rule satisfied for Be in this compound? If not, can you form an octet around Be by drawing another resonance structure? How plausible is this structure?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 67

Of the noble gases, only $\mathrm{Kr}, \mathrm{Xe},$ and $\mathrm{Rn}$ are known to form a few compounds with $\mathrm{O}$ and/or $\mathrm{F}$. Write Lewis structures for the following molecules:
(a) $\mathrm{XeF}_{2},$ (b) $\mathrm{XeF}_{4}$, (c) $\mathrm{XeF}_{6}$, (d) $\mathrm{XeOF}_{4}$, (e) $\mathrm{XeO}_{2} \mathrm{~F}_{2}$. In each case Xe is the central atom.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 68

Write a Lewis structure for $\mathrm{SbCl}_{5}$. Does this molecule obey the octet rule?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 69

Write Lewis structures for $\mathrm{SeF}_{4}$ and $\mathrm{SeF}_{6}$. Is the octet rule satisfied for Se?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 70

Write Lewis structures for the reaction
$$
\mathrm{AlCl}_{3}+\mathrm{Cl}^{-} \longrightarrow \mathrm{AlCl}_{4}^{-}
$$
What kind of bond joins Al and $\mathrm{Cl}$ in the product?

Cameron Oden

Numerade Educator

Problem 71

What is bond enthalpy? Bond enthalpies of polyatomic molecules are average values, whereas those of diatomic molecules can be accurately determined. Why?

Iryna Ivaniuk

Numerade Educator

Problem 72

Explain why the bond enthalpy of a molecule is usually defined in terms of a gas-phase reaction. Why are bond-breaking processes always endothermic and bond-forming processes always exothermic?

Freddie Montague

Freddie Montague

Numerade Educator

Problem 73

From the following data, calculate the average bond enthalpy for the $\mathrm{N}-\mathrm{H}$ bond:
$\begin{aligned} \mathrm{NH}_{3}(g) & \longrightarrow \mathrm{NH}_{2}(g)+\mathrm{H}(g) & \Delta H^{\circ} &=435 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{NH}_{2}(g) & \longrightarrow \mathrm{NH}(g)+\mathrm{H}(g) & \Delta H^{\circ} &=381 \mathrm{~kJ} / \mathrm{mol} \\ \mathrm{NH}(g) & \longrightarrow \mathrm{N}(g)+\mathrm{H}(g) & \Delta H^{\circ} &=360 \mathrm{~kJ} / \mathrm{mol} \end{aligned}$

Iryna Ivaniuk

Numerade Educator

Problem 74

For the reaction
$$
\mathrm{O}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}(g) \quad \Delta H^{\circ}=-107.2 \mathrm{~kJ} / \mathrm{mol}
$$
Calculate the average bond enthalpy in $\mathrm{O}_{3}$

Freddie Montague

Freddie Montague

Numerade Educator

Problem 75

For the reaction
$$
\mathrm{O}(g)+\mathrm{O}_{2}(g) \longrightarrow \mathrm{O}_{3}(g) \quad \Delta H^{\circ}=-107.2 \mathrm{~kJ} / \mathrm{mol}
$$
Calculate the average bond enthalpy in $\mathrm{O}_{3}$.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 76

For the reaction
$$
2 \mathrm{C}_{2} \mathrm{H}_{6}(g)+7 \mathrm{O}_{2}(g) \longrightarrow 4 \mathrm{CO}_{2}(g)+6 \mathrm{H}_{2} \mathrm{O}(g)
$$
(a) Predict the enthalpy of reaction from the average bond enthalpies in Table 9.4 .
(b) Calculate the enthalpy of reaction from the standard enthalpies of formation (see Appendix 2) of the reactant and product molecules, and compare the result with your answer for part (a).

Anand Jangid

Numerade Educator

Problem 77

Classify the following substances as ionic compounds or covalent compounds containing discrete molecules: $\mathrm{CH}_{4}, \mathrm{KF}, \mathrm{CO}, \mathrm{SiCl}_{4}, \mathrm{BaCl}_{2}$

Iryna Ivaniuk

Numerade Educator

Problem 78

Which of the following are ionic compounds? Which are covalent compounds? $\mathrm{RbCl}, \mathrm{PF}_{5}, \mathrm{BrF}_{3},$ $\mathrm{KO}_{2}, \mathrm{CI}_{4}$

Cameron Oden

Numerade Educator

Problem 79

Match each of the following energy changes with one of the processes given: ionization energy, electron affinity, bond enthalpy, and standard enthalpy of formation.
(a) $\mathrm{F}(g)+e^{-} \longrightarrow \mathrm{F}^{-}(g)$
(b) $\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{~F}(g)$
(c) $\mathrm{Na}(g) \longrightarrow \mathrm{Na}^{+}(g)+e^{-}$
(d) $\mathrm{Na}(s)+\frac{1}{2} \mathrm{~F}_{2}(g) \longrightarrow \mathrm{NaF}(s)$

Freddie Montague

Freddie Montague

Numerade Educator

Problem 80

The formulas for the fluorides of the third-period elements are $\mathrm{NaF}, \mathrm{MgF}_{2}, \mathrm{AlF}_{3}, \mathrm{SiF}_{4}, \mathrm{PF}_{5}, \mathrm{SF}_{6}$
and $\mathrm{ClF}_{3}$. Classify these compounds as covalent or ionic.

Cameron Oden

Numerade Educator

Problem 81

Use ionization energy (see Table 8.2 ) and electron affinity values (see Table 8.3 ) to calculate the energy change (in $\mathrm{kJ} / \mathrm{mol}$ ) for the following reactions:
(a) $\mathrm{Li}(g)+\mathrm{I}(g) \longrightarrow \mathrm{Li}^{+}(g)+\mathrm{I}^{-}(g)$
(b) $\mathrm{Na}(g)+\mathrm{F}(g) \longrightarrow \mathrm{Na}^{+}(g)+\mathrm{F}^{-}(g)$
(c) $\mathrm{K}(g)+\mathrm{Cl}(g) \longrightarrow \mathrm{K}^{+}(g)+\mathrm{Cl}^{-}(g)$

Iryna Ivaniuk

Numerade Educator

Problem 82

Describe some characteristics of an ionic compound such as $\mathrm{KF}$ that would distinguish it from a covalent compound such as benzene $\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)$.

Cameron Oden

Numerade Educator

Problem 83

Write Lewis structures for $\mathrm{BrF}_{3}, \mathrm{ClF}_{5},$ and $\mathrm{IF}_{7} .$ Identify those in which the octet rule is not obeyed.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 84

Write three reasonable resonance structures for the azide ion $\mathrm{N}_{3}^{-}$ in which the atoms are arranged as NNN. Show formal charges.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 85

The amide group plays an important role in determining the structure of proteins:
Draw another resonance structure for this group. Show formal charges.

Iryna Ivaniuk

Numerade Educator

Problem 86

Give an example of an ion or molecule containing Al that (a) obeys the octet rule, (b) has an expanded octet, and (c) has an incomplete octet.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 87

Draw four reasonable resonance structures for the $\mathrm{PO}_{3} \mathrm{~F}^{2-}$ ion. The central $\mathrm{P}$ atom is bonded to the three O atoms and to the $\mathrm{F}$ atom. Show formal charges.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 88

Attempts to prepare the compounds listed here as stable species under atmospheric conditions have failed. Suggest possible reasons for the failure. $\mathrm{CF}_{2}$ $\mathrm{LiO}_{2}, \mathrm{CsCl}_{2}, \mathrm{PI}_{5}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 89

Draw reasonable resonance structures for the following ions:
(a) $\mathrm{HSO}_{4}^{-},$ (b) $\mathrm{PO}_{4}^{3-},$ (c) $\mathrm{HSO}_{3}^{-}$ (d) $\mathrm{SO}_{3}^{2-}$. (Hint: See comment on Example $\left.9.11 .\right)$

Anand Jangid

Numerade Educator

Problem 90

Are the following statements true or false?
(a) Formal charges represent actual separation of charges. (b) $\Delta H_{\mathrm{rxn}}^{\circ}$ can be estimated from the bond enthalpies of reactants and products. (c) All secondperiod elements obey the octet rule in their compounds.
(d) The resonance structures of a molecule can be separated from one another.

Anand Jangid

Numerade Educator

Problem 91

A rule for drawing plausible Lewis structures is that the central atom is invariably less electronegative than the surrounding atoms. Explain why this is so. Why does this rule not apply to compounds like $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{NH}_{3} ?$

Iryna Ivaniuk

Numerade Educator

Problem 92

A rule for drawing plausible Lewis structures is that the central atom is invariably less electronegative than the surrounding atoms. Explain why this is so. Why does this rule not apply to compounds like $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{NH}_{3} ?$

Iryna Ivaniuk

Numerade Educator

Problem 93

Based on energy considerations, which of the following reactions will occur more readily?
(a) $\mathrm{Cl}(g)+\mathrm{CH}_{4}(g) \longrightarrow \mathrm{CH}_{3} \mathrm{Cl}(g)+\mathrm{H}(g)$
(b) $\mathrm{Cl}(g)+\mathrm{CH}_{4}(g) \longrightarrow \mathrm{CH}_{3}(g)+\mathrm{HCl}(g)$
(Hint: Refer to Table $9.4,$ and assume that the average bond enthalpy of the $\mathrm{C}-\mathrm{Cl}$ bond is $338 \mathrm{~kJ} / \mathrm{mol} .)$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 94

Which of the following molecules has the shortest nitrogen-to-nitrogen bond: $\mathrm{N}_{2} \mathrm{H}_{4}, \mathrm{~N}_{2} \mathrm{O}, \mathrm{N}_{2}, \mathrm{~N}_{2} \mathrm{O}_{4} ?$
Explain.

Cameron Oden

Numerade Educator

Problem 95

Most organic acids can be represented as $\mathrm{RCOOH}$ where $\mathrm{COOH}$ is the carboxyl group and $\mathrm{R}$ is the rest of the molecule. (For example, $\mathrm{R}$ is $\mathrm{CH}_{3}$ in acetic acid, $\mathrm{CH}_{3} \mathrm{COOH} .$ ) (a) Draw a Lewis structure for the carboxyl group. (b) Upon ionization, the carboxyl group is converted to the carboxylate group, $\mathrm{COO}^{-}$. Draw resonance structures for the carboxylate group.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 96

Which of the following species are isoelectronic:
$\mathrm{NH}_{4}^{+}, \mathrm{C}_{6} \mathrm{H}_{6}, \mathrm{CO}, \mathrm{CH}_{4}, \mathrm{~N}_{2}, \mathrm{~B}_{3} \mathrm{~N}_{3} \mathrm{H}_{6} ?$

Cameron Oden

Numerade Educator

Problem 97

The following species have been detected in interstellar space: (a) $\mathrm{CH},(\mathrm{b}) \mathrm{OH},(\mathrm{c}) \mathrm{C}_{2},(\mathrm{~d}) \mathrm{HNC},(\mathrm{e}) \mathrm{HCO} .$
Draw Lewis structures for these species and indicate whether they are diamagnetic or paramagnetic.

Iryna Ivaniuk

Numerade Educator

Problem 98

The amide ion, $\mathrm{NH}_{2}^{-},$ is a Bronsted base. Represent the reaction between the amide ion and water.

Cameron Oden

Numerade Educator

Problem 99

Draw Lewis structures for the following organic molecules: (a) tetrafluoroethylene $\left(\mathrm{C}_{2} \mathrm{~F}_{4}\right),$
(b) propane $\left(\mathrm{C}_{3} \mathrm{H}_{8}\right),(\mathrm{c})$ butadiene $\left(\mathrm{CH}_{2} \mathrm{CHCHCH}_{2}\right),$ (d) propyne
$\left(\mathrm{CH}_{3} \mathrm{CCH}\right),(\mathrm{e})$ benzoic acid $\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right) .$ (To draw
$\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH},$ replace a $\mathrm{H}$ atom in benzene with a COOH group.)

Freddie Montague

Freddie Montague

Numerade Educator

Problem 100

The triiodide ion $\left(\mathrm{I}_{3}^{-}\right)$ in which the I atoms are arranged in a straight line is stable, but the corresponding $\mathrm{F}_{3}^{-}$ ion does not exist. Explain.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 101

Compare the bond enthalpy of $\mathrm{F}_{2}$ with the energy change for the following process:
$$
\mathrm{F}_{2}(g) \longrightarrow \mathrm{F}^{+}(g)+\mathrm{F}^{-}(g)
$$
Which is the preferred dissociation for $\mathrm{F}_{2}$, energetically speaking?

Iryna Ivaniuk

Numerade Educator

Problem 102

Methyl isocyanate $\left(\mathrm{CH}_{3} \mathrm{NCO}\right)$ is used to make certain pesticides. In December $1984,$ water leaked into a tank containing this substance at a chemical plant, producing a toxic cloud that killed thousands of people in Bhopal, India. Draw Lewis structures for $\mathrm{CH}_{3} \mathrm{NCO},$ showing formal charges.

Cameron Oden

Numerade Educator

Problem 103

The chlorine nitrate molecule (ClONO $_{2}$ ) is believed to be involved in the destruction of ozone in the Antarctic stratosphere. Draw a plausible Lewis structure for this molecule.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 104

Several resonance structures for the molecule $\mathrm{CO}_{2}$ are shown. Explain why some of them are likely to be of little importance in describing the bonding in this molecule.

Anand Jangid

Numerade Educator

Problem 105

For each of the following organic molecules draw a Lewis structure in which the carbon atoms are bonded to each other by single bonds: (a) $\mathrm{C}_{2} \mathrm{H}_{6}$
(b) $\mathrm{C}_{4} \mathrm{H}_{10},$ (c) $\mathrm{C}_{5} \mathrm{H}_{12}$. For (b) and (c), show only structures in which each $\mathrm{C}$ atom is bonded to no more than two other $\mathrm{C}$ atoms.

Iryna Ivaniuk

Numerade Educator

Problem 107

Draw Lewis structures for the following organic molecules. In each there is one $\mathrm{C}=\mathrm{C}$ bond, and the rest of the carbon atoms are joined by $\mathrm{C}-\mathrm{C}$ bonds. $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{~F}, \mathrm{C}_{3} \mathrm{H}_{6}, \mathrm{C}_{4} \mathrm{H}_{8}$

Freddie Montague

Freddie Montague

Numerade Educator

Problem 108

Calculate $\Delta H^{\circ}$ for the reaction
$$
\mathrm{H}_{2}(g)+\mathrm{I}_{2}(g) \longrightarrow 2 \mathrm{HI}(g)
$$
using (a) Equation (9.3) and (b) Equation (6.18), given that $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{I}_{2}(g)$ is $61.0 \mathrm{~kJ} / \mathrm{mol} .$

Cameron Oden

Numerade Educator

Problem 109

Draw Lewis structures for the following organic molecules: (a) methanol $\left(\mathrm{CH}_{3} \mathrm{OH}\right) ;$
(b) ethanol $\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\right) ;$ (c) tetraethyllead $\left[\mathrm{Pb}\left(\mathrm{CH}_{2} \mathrm{CH}_{3}\right)_{4}\right]$
which was used in "leaded gasoline"; (d) methylamine $\left(\mathrm{CH}_{3} \mathrm{NH}_{2}\right),$ which is used in tanning; (e) mustard gas $\left(\mathrm{ClCH}_{2} \mathrm{CH}_{2} \mathrm{SCH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\right),$ a poisonous gas used in
World War I; (f) urea [(NH $_{2}$ ) $_{2}$ CO], a fertilizer; and
(g) glycine $\left(\mathrm{NH}_{2} \mathrm{CH}_{2} \mathrm{COOH}\right)$, an amino acid.

Iryna Ivaniuk

Numerade Educator

Problem 110

Write Lewis structures for the following four isoelectronic species: (a) $\mathrm{CO},(\mathrm{b}) \mathrm{NO}^{+},(\mathrm{c}) \mathrm{CN}^{-}$ (d) $\mathrm{N}_{2}$. Show formal charges.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 111

Oxygen forms three types of ionic compounds in which the anions are oxide $\left(\mathrm{O}^{2-}\right),$ peroxide $\left(\mathrm{O}_{2}^{2-}\right),$ and superoxide $\left(\mathrm{O}_{2}^{-}\right) .$ Draw Lewis structures of these ions.

Iryna Ivaniuk

Numerade Educator

Problem 112

Comment on the correctness of the statement, "All compounds containing a noble gas atom violate the octet rule."

Cameron Oden

Numerade Educator

Problem 113

Write three resonance structures for (a) the cyanate ion $\left(\mathrm{NCO}^{-}\right)$ and $(\mathrm{b})$ the isocyanate ion $\left(\mathrm{CNO}^{-}\right) .$ In each case, rank the resonance structures in order of increasing importance.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 114

(a) From the following data calculate the bond enthalpy of the $\mathrm{F}_{2}^{-}$ ion.
$$
\begin{aligned}
\mathrm{F}_{2}(g) \longrightarrow 2 \mathrm{~F}(g) & \Delta H_{\mathrm{rxn}}^{\circ}=156.9 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{F}^{-}(g) \longrightarrow \mathrm{F}(g)+e^{-} & \Delta H_{\mathrm{rxn}}^{\circ}=333 \mathrm{~kJ} / \mathrm{mol} \\
\mathrm{F}_{2}(g) \longrightarrow \mathrm{F}_{2}(g)+e^{-} & \Delta H_{\mathrm{rxn}}^{\circ}=290 \mathrm{~kJ} / \mathrm{mol}
\end{aligned}
$$
(b) Explain the difference between the bond enthalpies of $\mathrm{F}_{2}$ and $\mathrm{F}_{2}^{-}$

Cameron Oden

Numerade Educator

Problem 115

The resonance concept is sometimes described by analogy to a mule, which is a cross between a horse and a donkey. Compare this analogy with the one used in this chapter, that is, the description of a rhinoceros as a cross between a griffin and a unicorn. Which description is more appropriate? Why?

Iryna Ivaniuk

Numerade Educator

Problem 116

What are the other two reasons for choosing (b) in Example $9.7 ?$

Cameron Oden

Numerade Educator

Problem 117

In the Chemistry in Action essay "Just Say NO," nitric oxide is said to be one of about 10 of the smallest stable molecules known. Based on what you have learned in the course so far, write all the diatomic molecules you know, give their names, and show their Lewis structures.

Anand Jangid

Numerade Educator

Problem 118

The $\mathrm{N}-\mathrm{O}$ bond distance in nitric oxide is $115 \mathrm{pm}$ which is intermediate between a triple bond (106 pm) and a double bond (120 pm). (a) Draw two resonance structures for $\mathrm{NO}$ and comment on their relative importance. (b) Is it possible to draw a resonance structure having a triple bond between the atoms?

Cameron Oden

Numerade Educator

Problem 119

Write the formulas of the binary hydride for the second-period elements LiH to HF. Comment on the change from ionic to covalent character of these compounds. Note that beryllium behaves differently from the rest of the Group 2 A metals (see Section 8.6 ).

Anand Jangid

Numerade Educator

Problem 120

Hydrazine borane, $\mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}$, has been proposed as a hydrogen storage material. When reacted with lithium hydride (LiH), hydrogen gas is released:
$$
\mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}+\mathrm{LiH} \longrightarrow \mathrm{LiNH}_{2} \mathrm{NHBH}_{3}+\mathrm{H}_{2}
$$
Write Lewis structures for $\mathrm{NH}_{2} \mathrm{NH}_{2} \mathrm{BH}_{3}$ and $\mathrm{NH}_{2} \mathrm{NHBH}_{3}^{-}$ and assign all formal charges.

Cameron Oden

Numerade Educator

Problem 121

Although nitrogen dioxide $\left(\mathrm{NO}_{2}\right)$ is a stable compound, there is a tendency for two such molecules to combine to form dinitrogen tetroxide $\left(\mathrm{N}_{2} \mathrm{O}_{4}\right) .$ Why? Draw four resonance structures of $\mathrm{N}_{2} \mathrm{O}_{4},$ showing formal charges.

Iryna Ivaniuk

Numerade Educator

Problem 122

Another possible skeletal structure for the $\mathrm{CO}_{3}^{2-}$ (carbonate) ion besides the one presented in Example 9.5 is $\mathrm{O} \mathrm{C} \mathrm{O}$ O. Why would we not use this structure to represent $\mathrm{CO}_{3}^{2-} ?$

Anand Jangid

Numerade Educator

Problem 123

Draw a Lewis structure for nitrogen pentoxide $\left(\mathrm{N}_{2} \mathrm{O}_{5}\right)$ in which each $\mathrm{N}$ is bonded to three $\mathrm{O}$ atoms.

Iryna Ivaniuk

Numerade Educator

Problem 124

In the gas phase, aluminum chloride exists as a dimer (a unit of two) with the formula $\mathrm{Al}_{2} \mathrm{Cl}_{6}$. Its skeletal structure is given by
Complete the Lewis structure and indicate the coordinate covalent bonds in the molecule.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 125

The hydroxyl radical (OH) plays an important role in atmospheric chemistry. It is highly reactive and has a tendency to combine with a $\mathrm{H}$ atom from other compounds, causing them to break up. Thus, $\mathrm{OH}$ is sometimes called a "detergent" radical because it helps to clean up the atmosphere.
(a) Write the Lewis structure for the radical.
(b) Refer to Table 9.4 and explain why the radical has a high affinity for $\mathrm{H}$ atoms. (c) Estimate the enthalpy change for the reaction
$$
\mathrm{OH}(g)+\mathrm{CH}_{4}(g) \longrightarrow \mathrm{CH}_{3}(g)+\mathrm{H}_{2} \mathrm{O}(g)
$$
(d) The radical is generated when sunlight hits water vapor. Calculate the maximum wavelength (in nanometers) required to break an $\mathrm{O}-\mathrm{H}$ bond in $\mathrm{H}_{2} \mathrm{O}$

Iryna Ivaniuk

Numerade Educator

Problem 126

Experiments show that it takes $1656 \mathrm{~kJ} / \mathrm{mol}$ to break all the bonds in methane $\left(\mathrm{CH}_{4}\right)$ and $4006 \mathrm{~kJ} / \mathrm{mol}$ to break all the bonds in propane $\left(\mathrm{C}_{3} \mathrm{H}_{8}\right) .$ Based on these data, calculate the average bond enthalpy of the $\mathrm{C}-\mathrm{C}$ bond.

Freddie Montague

Freddie Montague

Numerade Educator

Problem 127

Calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ at $25^{\circ} \mathrm{C}$ of the reaction between carbon monoxide and hydrogen shown here using both bond enthalpy and $\Delta H_{\mathrm{f}}^{\circ}$ values.

Iryna Ivaniuk

Numerade Educator

Problem 128

Calculate $\Delta H_{\mathrm{rxn}}^{\circ}$ at $25^{\circ} \mathrm{C}$ of the reaction between ethylene and chlorine shown here using both bond enthalpy and $\Delta H_{\mathrm{f}}^{\circ}$ values. $\left(\Delta H_{\mathrm{f}}^{\circ}\right.$ for $\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Cl}_{2}$ is $-132 \mathrm{~kJ} / \mathrm{mol} .)$

Iryna Ivaniuk

Numerade Educator

Problem 129

Draw three resonance structures of sulfur dioxide $\left(\mathrm{SO}_{2}\right) .$ Indicate the most plausible structure(s).

Iryna Ivaniuk

Numerade Educator

Problem 131

In 1998 scientists using a special type of electron microscope were able to measure the force needed to break a single chemical bond. If $2.0 \times 10^{29} \mathrm{~N}$ was needed to break a $\mathrm{C}-\mathrm{Si}$ bond, estimate the bond enthalpy in $\mathrm{kJ} / \mathrm{mol} .$ Assume that the bond had to be stretched by a distance of 2 A $\left(2 \times 10^{-10} \mathrm{~m}\right)$ before it is broken.

Iryna Ivaniuk

Numerade Educator

Problem 132

The American chemist Robert S. Mulliken suggested a different definition for the electronegativity (EN) of an element, given by
$$
\mathrm{EN}=\frac{\mathrm{IE}+\mathrm{EA}}{2}
$$
where IE is the first ionization energy and EA the electron affinity of the element. Calculate the electronegativities of $\mathrm{O}, \mathrm{F},$ and $\mathrm{Cl}$ using this equation. Compare the electronegativities of these elements on the Mulliken and Pauling scale. (To convert to the Pauling scale, divide each EN value by $230 \mathrm{~kJ} / \mathrm{mol} .)$

Cameron Oden

Numerade Educator

Problem 133

Among the common inhaled anesthetics are:
halothane: $\mathrm{CF}_{3} \mathrm{CHClBr}$
enflurane: CHFClCF $_{2} \mathrm{OCHF}_{2}$
isoflurane: $\mathrm{CF}_{3} \mathrm{CHClOCHF}_{2}$
methoxyflurane: $\mathrm{CHCl}_{2} \mathrm{CF}_{2} \mathrm{OCH}_{3}$
Draw Lewis structures of these molecules.

Iryna Ivaniuk

Numerade Educator

Problem 134

A student in your class claims that magnesium oxide actually consists of $\mathrm{Mg}^{+}$ and $\mathrm{O}^{-}$ ions, not $\mathrm{Mg}^{2+}$ and $\mathrm{O}^{2-}$ ions. Suggest some experiments one could do to show that your classmate is wrong.

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 135

Shown here is a skeletal structure of borazine $\left(\mathrm{B}_{3} \mathrm{~N}_{3} \mathrm{H}_{6}\right) .$ Draw two resonance structures of the molecule, showing all the bonds and formal charges. Compare its properties with the isoelectronic molecule benzene.

Iryna Ivaniuk

Numerade Educator

Problem 136

Calculate the wavelength of light needed to carry out the reaction
$$
\mathrm{H}_{2} \longrightarrow \mathrm{H}^{+}+\mathrm{H}^{-}
$$

Anand Jangid

Numerade Educator

Problem 137

Sulfuric acid $\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right),$ the most important industrial chemical in the world, is prepared by oxidizing sulfur to sulfur dioxide and then to sulfur trioxide. Although sulfur trioxide reacts with water to form sulfuric acid, it forms a mist of fine droplets of $\mathrm{H}_{2} \mathrm{SO}_{4}$ with water vapor that is hard to condense. Instead, sulfur trioxide is first dissolved in 98 percent sulfuric acid to form oleum $\left(\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}\right) .$ On treatment with water, concentrated sulfuric acid can be generated. Write equations for all the steps and draw Lewis structures of oleum based on the discussion in Example $9.11 .$

Iryna Ivaniuk

Numerade Educator

Problem 138

From the lattice energy of $\mathrm{KCl}$ in Table 9.1 and the ionization energy of $\mathrm{K}$ and electron affinity of $\mathrm{Cl}$ in Tables 8.2 and $8.3,$ calculate the $\Delta H^{\circ}$ for the reaction
$$
\mathrm{K}(g)+\mathrm{Cl}(g) \longrightarrow \mathrm{KCl}(s)
$$

Cameron Oden

Numerade Educator

Problem 139

From the lattice energy of $\mathrm{KCl}$ in Table 9.1 and the ionization energy of $\mathrm{K}$ and electron affinity of $\mathrm{Cl}$ in Tables 8.2 and 8.3 , calculate the $\Delta H^{\circ}$ for the reaction
$$
\mathrm{K}(g)+\mathrm{Cl}(g) \longrightarrow \mathrm{KCl}(s)
$$
(a) Draw three resonance structures to represent the ion.
(b) Given the following information
$$
2 \mathrm{H}+\mathrm{H}^{+} \longrightarrow \mathrm{H}_{3}^{+} \quad \Delta H^{\circ}=-849 \mathrm{~kJ} / \mathrm{mol}
$$
and
$$
\mathrm{H}_{2} \longrightarrow 2 \mathrm{H} \quad \Delta H^{\circ}=436.4 \mathrm{~kJ} / \mathrm{mol}
$$
calculate $\Delta H^{\circ}$ for the reaction
$$
\mathrm{H}^{+}+\mathrm{H}_{2} \longrightarrow \mathrm{H}_{3}^{+}
$$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 140

The bond enthalpy of the $\mathrm{C}-\mathrm{N}$ bond in the amide group of proteins (see Problem 9.87 ) can be treated as an average of $\mathrm{C}-\mathrm{N}$ and $\mathrm{C}=\mathrm{N}$ bonds. Calculate the maximum wavelength of light needed to break the bond.

Cameron Oden

Numerade Educator

Problem 140

The bond enthalpy of the $\mathrm{C}-\mathrm{N}$ bond in the amide group of proteins (see Problem 9.87) can be treated as an average of $\mathrm{C}-\mathrm{N}$ and $\mathrm{C}=\mathrm{N}$ bonds. Calculate the maximum wavelength of light needed to break the bond.

Cameron Oden

Numerade Educator

Problem 141

In 1999 an unusual cation containing only nitrogen $\left(\mathrm{N}_{5}^{+}\right)$ was prepared. Draw three resonance structures of the ion, showing formal charges. (Hint: The $\mathrm{N}$ atoms are joined in a linear fashion.)

Freddie Montague

Freddie Montague

Numerade Educator

Problem 142

Nitroglycerin, one of the most commonly used explosives, has the structure
The decomposition reaction is
$$
\begin{array}{r}
4 \mathrm{C}_{3} \mathrm{H}_{5} \mathrm{~N}_{3} \mathrm{O}_{9}(l) \longrightarrow \\
12 \mathrm{CO}_{2}(g)+10 \mathrm{H}_{2} \mathrm{O}(g)+6 \mathrm{~N}_{2}(g)+\mathrm{O}_{2}(g)
\end{array}
$$
The explosive action is the result of the heat released and the large increase in gaseous volume.
(a) Calculate the $\Delta H^{\circ}$ for the decomposition of one mole of nitroglycerin using both standard enthalpy of formation values and bond enthalpies. Assume that the two $\mathrm{O}$ atoms in the $\mathrm{NO}_{2}$ groups are attached to $\mathrm{N}$ with one single bond and one double bond.
(b) Calculate the combined volume of the gases at STP. (c) Assuming an initial explosion temperature of $3000 \mathrm{~K}$, estimate the pressure exerted by the gases using the result from (b). (The standard enthalpy of formation of nitroglycerin is $-371.1 \mathrm{~kJ} / \mathrm{mol} .$ )

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 143

Give a brief description of the medical uses of the following ionic compounds: $\mathrm{AgNO}_{3}, \mathrm{BaSO}_{4},$ $\mathrm{CaSO}_{4}, \mathrm{KI}, \mathrm{Li}_{2} \mathrm{CO}_{3}, \mathrm{Mg}(\mathrm{OH})_{2}, \mathrm{MgSO}_{4}, \mathrm{NaHCO}_{3}$ $\mathrm{Na}_{2} \mathrm{CO}_{3}, \mathrm{NaF}, \mathrm{TiO}_{2}, \mathrm{ZnO} .$ You would need to do a Web search of some of these compounds.

Iryna Ivaniuk

Numerade Educator

Problem 144

Use Table 9.4 to estimate the bond enthalpy of the $\mathrm{C}-\mathrm{C}, \mathrm{N}-\mathrm{N},$ and $\mathrm{O}-\mathrm{O}$ bonds in $\mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{~N}_{2} \mathrm{H}_{4},$ and
$\mathrm{H}_{2} \mathrm{O}_{2},$ respectively. What effect do lone pairs on adjacent atoms have on the strength of the particular bonds?

Cameron Oden

Numerade Educator

Problem 145

The isolated $\mathrm{O}^{2-}$ ion is unstable so it is not possible to measure the electron affinity of the $\mathrm{O}^{-}$ ion directly. Show how you can calculate its value by using the lattice energy of $\mathrm{MgO}$ and the Born-Haber cycle. [Useful information: $\mathrm{Mg}(s) \rightarrow \mathrm{Mg}(g) \Delta H^{\circ}=$ $148 \mathrm{~kJ} / \mathrm{mol} .]$

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 146

When irradiated with light of wavelength $471.7 \mathrm{nm}$ the chlorine molecule dissociates into chlorine atoms. One $\mathrm{Cl}$ atom is formed in its ground electronic state while the other is in an excited state that is
$10.5 \mathrm{~kJ} / \mathrm{mol}$ above the ground state. What is the bond enthalpy of the $\mathrm{Cl}_{2}$, molecule?

Kratika Bhadauria

Kratika Bhadauria

Numerade Educator

Problem 147

Recall from Chapter 8 that the product of the reaction between $\mathrm{Xe}(g)$ and $\mathrm{PtF}_{6}(g)$ was originally thought to be an ionic compound composed of $\mathrm{Xe}^{+}$ cations and $\mathrm{PtF}_{6}^{-}$ anions (see Figure 8.22 ). This prediction was based on the theoretical enthalpy of formation of $\mathrm{XePtF}_{6}$ calculated using a Born-Haber cycle. (a) The lattice energy for $\mathrm{XePtF}_{6}$ was estimated to be $460 \mathrm{~kJ} / \mathrm{mol}$. Explain whether or not this value is consistent with the lattice energies in Table $9.1 .$ (b) Calculate $\Delta H_{\mathrm{f}}^{\circ}$ for $\mathrm{XePtF}_{6}$ given IE $_{1}$ for $\mathrm{Xe}(g)$ is $1170 \mathrm{~kJ} / \mathrm{mol}$ and $\mathrm{EA}_{1}$ for $\mathrm{PtF}_{6}(g)$ is $770 \mathrm{~kJ} / \mathrm{mol} .$ Comment on the expected stability of $\mathrm{XePtF}_{6}$ based on your calculation.

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 148

The reaction between fluorine $\left(\mathrm{F}_{2}\right)$ with ethane $\left(\mathrm{C}_{2} \mathrm{H}_{6}\right)$ produces predominantly $\mathrm{CF}_{4}$ rather than $\mathrm{C}_{2} \mathrm{~F}_{6}$ molecules. Explain.

Cameron Oden

Numerade Educator

Problem 149

A new allotrope of oxygen, $\mathrm{O}_{4}$, has been reported. The exact structure of $\mathrm{O}_{4}$ is unknown, but the $\operatorname{sim}-$ plest possible structure would be a four-member ring consisting of oxygen-oxygen single bonds. The report speculated that the $\mathrm{O}_{4}$ molecule might be useful as a fuel "because it packs a lot of oxygen in a small space, so it might be even more energy-dense than the liquefied ordinary oxygen used in rocket fuel." (a) Draw a Lewis structure for $\mathrm{O}_{4}$ and write a balanced chemical equation for the reaction between ethane, $\mathrm{C}_{2} \mathrm{H}_{6}(g),$ and $\mathrm{O}_{4}(g)$ to give carbon dioxide and water vapor. (b) Estimate $\Delta H^{\circ}$ for the reaction. (c) Write a chemical equation illustrating the standard enthalpy of formation of $\mathrm{O}_{4}(g)$ and estimate $\Delta H_{\mathrm{f}}^{\circ}$ (d) Assuming the oxygen allotropes are in excess, which will release more energy when reacted with ethane (or any other fuel): $\mathrm{O}_{2}(g)$ or $\mathrm{O}_{4}(g) ?$ Explain using your answers to parts (a)-(c).

Susan Hallstrom

Susan Hallstrom

Numerade Educator

Problem 150

Because bond formation is exothermic, when two gas-phase atoms come together to form a diatomic molecule it is necessary for a third atom or molecule to absorb the energy that is released. Otherwise the molecule will undergo dissociation. If two atoms of hydrogen combine to form $\mathrm{H}_{2}(g),$ what would be the increase in velocity of a third hydrogen atom that absorbs the energy released from this process?

Cameron Oden

Numerade Educator

Problem 151

Estimate $\Delta H_{\mathrm{f}}^{\circ}$ for sodium astatide (NaAt) according to the equation
$$
\mathrm{Na}(s)+\frac{1}{2} \mathrm{At}_{2}(s) \longrightarrow \operatorname{NaAt}(s)
$$
The information in Problem 8.147 may be useful.

Susan Hallstrom

Susan Hallstrom

Numerade Educator