General Chemistry

Donald A. McQuarrie, Peter A. Rock, Ethan B. Gallogly

Chapter 7

Lewis Formulas - all with Video Answers

Educators

Chapter Questions

Problem 1

Pure hydrogen peroxide, $\mathrm{H}_{2} \mathrm{O}_{2}(l)$, is a colorless liquid that is caustic to the skin, but a $3 \%$ aqueous solution is a mild bleaching agent. Write the Lewis formula for a $\mathrm{H}_{2} \mathrm{O}_{2}$ molecule.

Nicole Smina

Nicole Smina

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Problem 2

Tetrafluorohydrazine, $\mathrm{N}_{2} \mathrm{~F}_{4}(l)$, is a colorless liquid that is used as rocket fuel. Write the Lewis formula for a tetrafluorohydrazine molecule.

Nicole Smina

Numerade Educator

Problem 3

Write the Lewis formula for the molecules
(a) $\mathrm{SCl}_{2}$
(b) $\mathrm{GeCl}_{4}$
(c) AsBr $_{3}$
(d) $\mathrm{PH}_{3}$

Nicholas Sacco

Numerade Educator

Problem 4

Write the Lewis formula for the molecules
(a) $\mathrm{PBr}_{3}$
(b) $\mathrm{SiF}_{4}$
(c) $\mathrm{NI}_{3}$
(d) $\mathrm{H}_{2} \mathrm{Se}$

Nicholas Sacco

Numerade Educator

Problem 5

Write the Lewis formula for the molecules
(a) methane, $\mathrm{CH}_{4}$
(b) fluoromethane, $\mathrm{CH}_{3} \mathrm{~F}$
(c) aminomethane, $\mathrm{CH}_{3} \mathrm{NH}_{2}$

Nicholas Sacco

Numerade Educator

Problem 6

Write the Lewis formula for the molecules
(a) methyl mercaptan, $\mathrm{CH}_{3} \mathrm{SH}$
(b) dimethyl ether, $\mathrm{CH}_{3} \mathrm{OCH}_{3}$
(c) trimethyl amine, $\mathrm{N}\left(\mathrm{CH}_{3}\right)_{3}$

Nicholas Sacco

Numerade Educator

Problem 7

Write the Lewis formula for the molecules
(a) acetylene, $\mathrm{C}_{2} \mathrm{H}_{2}$
(b) diazine, $\mathrm{N}_{2} \mathrm{H}_{2}$
(c) phosgene, $\mathrm{COCl}_{2}$
(d) fluorine cyanide, FCN

Nicholas Sacco

Numerade Educator

Problem 8

Write the Lewis formula for the molecules
(a) nitrous acid, $\mathrm{HNO}_{2}$
(b) silicon dioxide, $\mathrm{SiO}_{2}$
(c) propylene, $\mathrm{CH}_{3} \mathrm{CHCH}_{2}$
(d) perchloroethylene, $\mathrm{CCl}_{2} \mathrm{CCl}_{2}$

Nicholas Sacco

Numerade Educator

Problem 9

Vinyl chloride is an important industrial chemical used in the manufacture of polyvinyl chloride. Its chemical formula is $\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}$. Write the Lewis formula for a vinyl chloride molecule.

Nicholas Sacco

Numerade Educator

Problem 10

Azides of heavy metals explode when struck sharply and are used in detonation caps. Write the Lewis formula for the azide ion, $\mathrm{N}_{3}^{-}$

Nicole Smina

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Problem 11

Formic acid (systematic name: methanoic acid) is a colorless liquid with a penetrating odor. It is the irritating ingredient in the bite of ants. Its chemical formula is HCOOH. Write the Lewis formula for a formic acid molecule. (Hint: Each of the atoms in the correct formula has a zero formal charge.)

Nicholas Sacco

Numerade Educator

Problem 12

Acetone (systematic name: 2-propanone) is an organic compound widely used in the chemical industry as a solvent, for example, in paints and varnishes. You may be familiar with its sweet odor because it is used as a fingernail polish remover. Its chemical formula is $\mathrm{CH}_{3} \mathrm{COCH}_{3} .$ Write the Lewis formula for an acetone molecule.

Nicholas Sacco

Numerade Educator

Problem 13

Use formal charge considerations to rule out the Lewis formula for a $\mathrm{NF}_{3}$ molecule in which the nitrogen atom and the three fluorine atoms are connected in a row.

Nicole Smina

Numerade Educator

Problem 14

Use formal charge considerations to predict the arrangement of the atoms in a NOCl molecule.

Nicole Smina

Numerade Educator

Problem 15

Laughing gas, an anesthetic and a propellant in whipped-cream-dispensing cans, has the chemical formula $\mathrm{N}_{2} \mathrm{O} .$ Use Lewis formulas and formal charge considerations to predict which structure, NNO or NON, is the more likely.

Nicole Smina

Numerade Educator

Problem 16

Use formal charge considerations to rule out the Lewis formula for a $\mathrm{NO}_{2}^{-}$ ion in which the arrangement of the atoms is $\mathrm{O}-\mathrm{O}-\mathrm{N}$

Nicole Smina

Numerade Educator

Problem 17

Write Lewis formulas for the resonance forms of the formate ion, $\mathrm{HCOO}^{-} .$ Indicate formal charges and discuss the bonding of this ion.

Nicole Smina

Numerade Educator

Problem 18

Write Lewis formulas for the resonance forms of the acetate ion, $\mathrm{CH}_{3} \mathrm{COO}^{-}$. Indicate formal charges and discuss the bonding in this ion.

Nicole Smina

Numerade Educator

Problem 19

Write Lewis formulas for the resonance forms of the hydrogen carbonate (bicarbonate) ion, $\mathrm{HCO}_{3}^{-}$ Indicate formal charges and discuss the bonding in this ion.

Nicole Smina

Numerade Educator

Problem 20

Write Lewis formulas for the resonance forms of an ozone molecule, $\mathrm{O}_{3} .$ Indicate formal charges and discuss the bonding in this molecule.

Nicole Smina

Numerade Educator

Problem 21

Write the Lewis formula for the following benzene derivatives:
(a) chlorobenzene, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Cl}$
(b) aminobenzene, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{NH}_{2}$
(c) benzoic acid, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}$
(d) phenol, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{OH}$

Nicholas Sacco

Numerade Educator

Problem 22

Naphthalene, which gives mothballs their characteristic odor, has the formula $\mathrm{C}_{10} \mathrm{H}_{8}$. Given that its structure is two benzene rings fused together along one carbon-carbon bond, write its Lewis formula.

Nicole Smina

Numerade Educator

Problem 23

Which of the following species contain an odd number of electrons?
(a) $\mathrm{NO}_{2}$
(b) $\mathrm{CO}$
(c) $\mathrm{O}_{3}^{-}$
(d) $\mathrm{O}_{2}^{-}$
Write a Lewis formula for each of these species.

Ronald Prasad

Numerade Educator

Problem 24

Which of the following species contain an odd number of electrons?
(a) $\mathrm{BrO}_{3}$
(b) $\mathrm{SO}_{3}$
(c) HNO
(d) $\mathrm{HO}_{2}$
Write a Lewis formula for each of these species.

Ronald Prasad

Numerade Educator

Problem 25

Nitrosamines are carcinogens that are found in tobacco smoke. They can also be formed in the body from the nitrites and nitrates used to preserve processed meats, especially bacon and sausage. The simplest nitrosamine molecule is methylnitrosamine, $\mathrm{H}_{3}$ CNNO. Write the Lewis formula for this molecule. Is it a free radical?

Ronald Prasad

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Problem 26

Many free radicals combine to form molecules that do not contain any unpaired electrons. The driving force for the radical-radical combination reaction is the formation of a new electron-pair bond. Write Lewis formulas for the reactant and product species in the following chemical equations:
(a) $\mathrm{CH}_{3}(g)+\mathrm{CH}_{3}(g) \rightarrow \mathrm{H}_{3} \mathrm{CCH}_{3}(g)$
(b) $\mathrm{N}(g)+\mathrm{NO}(g) \rightarrow \mathrm{NNO}(g)$
(c) $2 \mathrm{OH}(g) \rightarrow \mathrm{H}_{2} \mathrm{O}_{2}(g)$

Ronald Prasad

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Problem 27

Write the Lewis formula for the ions
(a) $\mathrm{PCl}_{6}^{-}$
(b) $\mathrm{I}_{3}^{-}$
(c) $\operatorname{SiF}_{6}^{-}$
(d) $\mathrm{IO}_{2} \mathrm{~F}_{2}^{-}$

Ronald Prasad

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Problem 28

Write a Lewis formula for each of the following compounds of xenon:
$$
\begin{array}{clc}
\hline \text { Compound } & \text { Form at } 25^{\circ} \mathbf{C} & \text { Melting point } /{ }^{\circ} \mathbf{C} \\
\hline \mathrm{XeF}_{2} & \text { colorless crystals } & 129 \\
\mathrm{XeF}_{4} & \text { colorless crystals } & 117 \\
\mathrm{XeF}_{6} & \text { colorless crystals } & 50 \\
\mathrm{XeOF}_{4} & \text { colorless liquid } & -46 \\
\mathrm{XeO}_{2} \mathrm{~F}_{2} & \text { colorless crystals } & 31
\end{array}
$$

Ronald Prasad

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Problem 29

Write the Lewis formulas of the interhalogen compounds $\mathrm{IF}_{3}$ and $\mathrm{IF}_{5}$.

Nicole Smina

Numerade Educator

Problem 30

Write the Lewis formulas of the interhalogen ions $\mathrm{ICl}_{4}^{-}, \mathrm{IF}_{4}^{+}$, and $\mathrm{IF}_{2}^{-}$.

Ronald Prasad

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Problem 31

Write Lewis formulas for a sulfur tetrafluoride, $\mathrm{SF}_{4}$, and sulfur hexafluoride, $\mathrm{SF}_{6}$, molecule.

Nicole Smina

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Problem 32

Write Lewis formulas for a sulfinyl fluoride, $\mathrm{SOF}_{2}$, and sulfonyl fluoride, $\mathrm{SO}_{2} \mathrm{~F}_{2}$, molecule.

Ronald Prasad

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Problem 33

Using only a periodic table as a guide, arrange the following atoms in order of decreasing electronegativity:
$\begin{array}{lllll}\text { Na } & \text { S } & \text { Si } & \text { F } & \text { O }\end{array}$

Ronald Prasad

Numerade Educator

Problem 34

Using only a periodic table as a guide, arrange the following atoms in order of decreasing electronegativity:
$\begin{array}{llll}\text { In } & \text {Se } & \text { Sb } & \text { Cl } & \text { S }\end{array}$

Ronald Prasad

Numerade Educator

Problem 35

Arrange the following groups of molecules in order of increasing dipole moment:
$\begin{aligned}&\text { (a) HCl HF } & \text { HI } & \text { HBr } \quad \text { (linear molecules) }\end{aligned}$
$\begin{array}{llll}\text { (b) } \mathrm{PH}_{3} & \mathrm{NH}_{3} & \mathrm{AsH}_{3} & \text { (tripod-shaped molecules) }\end{array}$
$\begin{array}{llll}\text { (c) } \mathrm{Cl}_{2} \mathrm{O} & \mathrm{F}_{2} \mathrm{O} & \mathrm{H}_{2} \mathrm{O}\end{array}$
(bent molecules)

Adriano Chikande

Adriano Chikande

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Problem 36

Arrange the following groups of molecules in order of increasing dipole moment:
$\begin{array}{llll}\text { (a) } \mathrm{ClF}_{3} & \mathrm{BrF}_{3} & \mathrm{IF}_{3}\end{array}$ (T-shaped molecules)
$\begin{array}{llll}\text { (b) } \mathrm{H}_{2} \mathrm{O} & \mathrm{H}_{2} \mathrm{~S} & \mathrm{H}_{2} \mathrm{Te} & \mathrm{H}_{2} \mathrm{Se} & \text { (bent molecules) }\end{array}$
$\begin{array}{llll}\text { (c) } \mathrm{O}_{3} & \mathrm{SO}_{2} & \mathrm{H}_{2} \mathrm{~S} & \text { (bent molecules) }\end{array}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 37

Describe the charge distribution in the following molecules:
(a) nitrogen trifluoride, $\mathrm{NF}_{3}$
(b) oxygen difluoride, $\mathrm{OF}_{2}$
(c) oxygen dibromide, $\mathrm{OBr}_{2}$

Nicole Smina

Numerade Educator

Problem 38

Describe the charge distribution in the following molecules:
(a) hydrogen fluoride, HF
(b) phosphine, $\mathrm{PH}_{3}$
(c) hydrogen sulfide, $\mathrm{H}_{2} \mathrm{~S}$

Nicole Smina

Numerade Educator

Problem 39

A solution of sugar in water is a poor conductor of electricity, whereas a solution of table salt in water is a good conductor of electricity. What does this tell you about the bonding in the two substances?

Nicole Smina

Numerade Educator

Problem 40

What is a chemical bond? What kinds of chemical bonds are there? How do we distinguish between each type of chemical bond?

Nicole Smina

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Problem 41

The octet rule states that atoms and ions with eight electrons in their valence shell are more stable than those with fewer than eight electrons. Does this rule hold for all atoms in the periodic table?

Nicole Smina

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Problem 42

What is meant by "delocalized charge"?

Nicole Smina

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Problem 43

Explain why phosphorous pentafluoride molecules, $\mathrm{PF}_{5}$, exist in nature, whereas nitrogen pentafluoride molecules, $\mathrm{NF}_{5}$, do not-even though the elements phosphorous and nitrogen are in the same family in the periodic table.

Nicole Smina

Numerade Educator

Problem 44

Write the Lewis formula, show the formal charges, and discuss the bonding for
(a) the sulfate ion, $\mathrm{SO}_{4}^{2-}$
(b) the phosphate ion, $\mathrm{PO}_{4}^{3-}$
(c) the acetate ion, $\mathrm{CH}_{3} \mathrm{CO}_{2}^{-}$

Adriano Chikande

Adriano Chikande

Numerade Educator

Problem 45

The halogens form a number of interhalogen compounds. For example, chlorine pentafluoride, $\mathrm{ClF}_{5}(g)$, can be prepared according to the following chemical equation:
$$
\mathrm{KCl}(s)+3 \mathrm{~F}_{2}(g) \rightarrow \mathrm{ClF}_{5}(g)+\mathrm{KF}(s)
$$
The halogen fluorides are very reactive, combining explosively with water, for example. Write the Lewis formula for each of the following halogen fluoride species:
(a) $\mathrm{ClF}_{5}$
(b) $\mathrm{IF}_{3}$
(c) $\mathrm{IF}_{7}$
(d) $\mathrm{IF}_{4}^{+}$

Ronald Prasad

Numerade Educator

Problem 46

Write the Lewis formula for
(a) the tetrafluoroammonium ion, $\mathrm{NF}_{4}^{+}$
(b) the tetrafluorochlorinium ion, $\mathrm{ClF}_{4}^{+}$
(c) the phosphonium ion, $\mathrm{PH}_{4}^{+}$
(d) the hexafluoroarsenate ion, $\mathrm{AsF}_{6}^{-}$
(e) the tetrafluorobromate ion, $\mathrm{BrF}_{4}^{-}$

Ronald Prasad

Numerade Educator

Problem 47

Write the Lewis formula for each of the following oxychlorine species:
(a) perchlorate ion, $\mathrm{ClO}_{4}^{-}$
(b) chlorine oxide, $\mathrm{ClO}$
(c) chlorate ion, $\mathrm{ClO}_{3}^{-}$
(d) chlorine dioxide, $\mathrm{ClO}_{2}$
(e) hypochlorite ion, $\mathrm{ClO}^{-}$

Ronald Prasad

Numerade Educator

Problem 48

Write the Lewis formula for each of the following acid molecules:
(a) $\mathrm{HClO}_{3}$
(b) $\mathrm{HNO}_{2}$
(c) $\mathrm{HIO}_{4}$
(d) $\mathrm{HBrO}_{2}$

Ronald Prasad

Numerade Educator

Problem 49

Write the Lewis formula for each of the following oxyacids of sulfur:
(a) sulfuric acid, $\mathrm{H}_{2} \mathrm{SO}_{4}$
(b) thiosulfuric acid, $\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}$
(c) disulfuric acid, $\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{7}$ (has a $\mathrm{S}-\mathrm{O}-\mathrm{S}$ bond $)$
(d) dithionic acid, $\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{6}$ (has a $\mathrm{S}-\mathrm{S}$ bond $)$
(e) peroxydisulfuric acid, $\mathrm{H}_{2} \mathrm{~S}_{2} \mathrm{O}_{8}$ (has an $\mathrm{O}-\mathrm{O}$ bond)

Ronald Prasad

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Problem 50

Sulfur forms a number of fluorides. Some of them are
(a) $\mathrm{SF}_{2}$
(b) $\mathrm{SF}_{4}$
(c) $\mathrm{S}_{2} \mathrm{~F}_{10}$
(d) $\mathrm{S}_{2} \mathrm{~F}_{2}$
Write a Lewis formula for each of these fluoride mol-
ecules.

Ronald Prasad

Numerade Educator

Problem 51

Phosphorus forms a number of oxohalides, $\mathrm{X}_{3} \mathrm{PO}$, in which $\mathrm{X}$ may be a $\mathrm{F}, \mathrm{Cl}$, or $\mathrm{Br}$ atom. The most common of these, phosphoryl chloride, is obtained as follows:
$$
2 \mathrm{PCl}_{3}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{Cl}_{3} \mathrm{PO}(g)
$$
Write the Lewis formula for a phosphoryl halide molecule.

Nicole Smina

Numerade Educator

Problem 52

In the $\mathrm{P}_{4} \mathrm{O}_{6}$ molecule each phosphorus atom is bonded to three oxygen atoms and each oxygen atom is bonded to two phosphorus atoms. Write a Lewis formula for the $\mathrm{P}_{4} \mathrm{O}_{6}$ molecule.

Nicole Smina

Numerade Educator

Problem 53

Indicate whether or not molecules of the following species have a triple bond.
(a) $\mathrm{CH}_{2} \mathrm{CHCN}$
(b) $\mathrm{HOOCCOOH}$
(c) $\mathrm{C}_{2}^{2-}$
(d) $\mathrm{CH}_{3} \mathrm{CHCH}_{2}$

Nicholas Sacco

Numerade Educator

Problem 54

Use Lewis formulas and formal charge considerations to suggest that the structure of an $\mathrm{N}_{2} \mathrm{~F}_{2}$ molecule is FNNF rather than FFNN or NFFN.

Ronald Prasad

Numerade Educator

Problem 55

Use Lewis formulas and formal charge considerations to suggest that the structure of a hydrocyanic acid molecule is HCN rather than HNC.

Nicole Smina

Numerade Educator

Problem 56

An alcohol is an organic compound containing an OH group. Write the Lewis formula for molecules of the following alcohols (common names are given in parentheses):
(a) ethanol (ethyl alcohol), $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}$
(b) 1-propanol ( $n$ -propyl alcohol), $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
(c) 2-propanol (isopropyl alcohol), $\left(\mathrm{CH}_{3}\right)_{2}$ CHOH

Ronald Prasad

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Problem 57

Write all the possible Lewis formulas for a molecule with the chemical formula $\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Cl}_{2}$.

Nicole Smina

Numerade Educator

Problem 58

Write the Lewis formula for a bromine chloride molecule and indicate its dipole moment.

Ronald Prasad

Numerade Educator

Problem 59

A hydroxide ion, $\mathrm{OH}^{-}$, results when a proton is removed from a $\mathrm{H}_{2} \mathrm{O}$ molecule. The ion that results when a proton is removed from a $\mathrm{H}_{2} \mathrm{O}_{2}$ molecule is called a hydroperoxide ion, $\mathrm{HO}_{2}^{-}$. Write the Lewis formula for a hydroperoxide ion. Name the following ionic compounds: $\mathrm{NaHO}_{2}$ and $\mathrm{Ba}\left(\mathrm{HO}_{2}\right)_{2}$.

Ronald Prasad

Numerade Educator

Problem 60

A methoxide ion, $\mathrm{CH}_{3} \mathrm{O}^{-}$, results when a proton is removed from a methanol molecule, $\mathrm{CH}_{3} \mathrm{OH}$. Write the Lewis formula for a $\mathrm{CH}_{3} \mathrm{O}^{-}$ ion. Name the compounds $\mathrm{KOCH}_{3}$ and $\mathrm{Al}\left(\mathrm{OCH}_{3}\right)_{3}$.

Ronald Prasad

Numerade Educator

Problem 61

Write the Lewis formula for each of the following species. Give resonance forms where appropriate and indicate formal charges.
(a) $\mathrm{CS}_{3}^{2-}$
(b) $\mathrm{C}_{2} \mathrm{O}_{4}^{2-}$
(c) NCS $^{-}$

Nicole Smina

Numerade Educator

Problem 62

Write the Lewis formula for each of the following nitrogen oxide molecules. Indicate formal charge and resonance forms.
$$
\begin{array}{lll}
\text { Formula } & \text { Name } & \text { Form at } 25^{\circ} \mathbf{C}, 1 \text { atm } \\
\hline \mathrm{N}_{2} \mathrm{O} & \text { dinitrogen oxide } & \text { colorless gas } \\
\mathrm{NO} & \text { nitrogen oxide } & \text { colorless gas } \\
\mathrm{N}_{2} \mathrm{O}_{3} & \text { dinitrogen trioxide } & \text { dark blue gas } \\
\mathrm{NO}_{2} & \text { nitrogen dioxide } & \text { brown gas } \\
\mathrm{N}_{2} \mathrm{O}_{4} & \text { dinitrogen tetroxide } & \text { colorless gas } \\
\mathrm{N}_{2} \mathrm{O}_{5} & \text { dinitrogen pentoxide } & \text { white solid }
\end{array}
$$

Ronald Prasad

Numerade Educator

Problem 63

Solid sulfur consists of eight-membered rings of sulfur atoms. Write the Lewis formula for a $\mathrm{S}_{8}$ molecule.

Ronald Prasad

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Problem 64

Write Lewis formulas for the resonance forms of the thiosulfate ion, $\mathrm{S}_{2} \mathrm{O}_{3}^{2-} .$ Indicate formal charges and discuss the bonding in this ion.

Nicole Smina

Numerade Educator

Problem 65

White phosphorous has the chemical formula $\mathrm{P}_{4}(s) .$ A $\mathrm{P}_{4}$ molecule has 20 valence electrons. Draw a Lewis formula for a white phosphorous molecule in which none of the atoms violates the octet rule and the formal charge on each atom is zero.

Ronald Prasad

Numerade Educator