C H A P T E R 6 R E V I E W
Chemical Bonding
SECTION 1
SHORT ANSWER Answer the following questions in the space provided.
a1. A chemical bond between atoms results from the attraction between the valence electrons and of different atoms.
(a) nuclei (c) isotopes(b) inner electrons (d) Lewis structures
b2. A covalent bond consists of
(a) a shared electron. (c) two different ions.(b) a shared electron pair. (d) an octet of electrons.
a3. If two covalently bonded atoms are identical, the bond is identified as
(a) nonpolar covalent. (c) ionic.(b) polar covalent. (d) dipolar.
b4. A covalent bond in which there is an unequal attraction for the sharedelectrons is
(a) nonpolar. (c) ionic.(b) polar. (d) dipolar.
c5. Atoms with a strong attraction for electrons they share with another atomexhibit
(a) zero electronegativity. (c) high electronegativity.(b) low electronegativity. (d) Lewis electronegativity.
c6. Bonds that possess between 5% and 50% ionic character are considered to be
(a) ionic. (c) polar covalent.(b) pure covalent. (d) nonpolar covalent.
a7. The greater the electronegativity difference between two atoms bonded together, thegreater the bond’s percentage of
(a) ionic character. (c) metallic character.(b) nonpolar character. (d) electron sharing.
8. The electrons involved in the formation of a chemical bond are called
valence electrons .
9. A chemical bond that results from the electrostatic attraction between positive and
ionic bondnegative ions is called a(n) .
MODERN CHEMISTRY CHEMICAL BONDING 41Copyright © by Holt, Rinehart and Winston. All rights reserved.
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SECTION 1 continued
10. If electrons involved in bonding spend most of the time closer to one atom rather than
polar covalentthe other, the bond is .
11. If a bond’s character is more than 50% ionic, then the bond is called
ionic bonda(n) .
12. A bond’s character is more than 50% ionic if the electronegativity difference between the two
1.7atoms is greater than .
13. Write the formula for an example of each of the following compounds:
Answers will vary.H2 a. nonpolar covalent compound
HCl b. polar covalent compound
NaCl c. ionic compound
14. Describe how a covalent bond holds two atoms together.
A pair of electrons is attracted to both nuclei of the two atoms bonded together.
15. What property of the two atoms in a covalent bond determines whether or not the bond will bepolar?
electronegativity
16. How can electronegativity be used to distinguish between an ionic bond and a covalent bond?
The difference between the electronegativity of the two atoms in a bond will
determine whether the bond is ionic or covalent. If the difference in
electronegativity is greater than 1.7, the bond is considered ionic.
17. Describe the electron distribution in a polar-covalent bond and its effect on the partial charges ofthe compound.
The electron density is greater around the more electronegative atom, giving that
part of the compound a partial negative charge. The other part of the compound
has an equal partial positive charge.
42 CHEMICAL BONDING MODERN CHEMISTRYCopyright © by Holt, Rinehart and Winston. All rights reserved.
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C H A P T E R 6 R E V I E W
Chemical Bonding
SECTION 2
SHORT ANSWER Answer the following questions in the space provided.
1. Use the concept of potential energy to describe how a covalent bond forms between two atoms.
As the atoms involved in the formation of a covalent bond approach each other, the
electron-proton attraction is stronger than the electron-electron and proton-proton
repulsions. The atoms are drawn to each other and their potential energy decreases.
Eventually, a distance is reached at which the repulsions between the like charges
equals the attraction of the opposite charges. At this point, potential energy is at a
minimum and a stable molecule forms.
2. Name two elements that form compounds that can be exceptions to the octet rule.
Choose from hydrogen, boron, beryllium, phosphorus, sulfur, and xenon.
3. Explain why resonance structures are used instead of Lewis structures to correctly model certainmolecules.
Resonance structures show that one Lewis structure cannot correctly represent
the location of electrons in a bond. Resonance structures show delocalized
electrons, while Lewis structures depict electrons in a definite location.
4. Bond energy is related to bond length. Use the data in the tables below to arrange the bonds listedin order of increasing bond length, from shortest bond to longest.
a.Bond Bond energy (kJ/mol)
H—F 569
H—I 299
H—Cl 432
H—Br 366
H—F, H—Cl, H—Br, H—I
MODERN CHEMISTRY CHEMICAL BONDING 43Copyright © by Holt, Rinehart and Winston. All rights reserved.
Name Date Class
SECTION 2 continued
b.Bond Bond energy (kJ/mol)
C—C 346
C———C 835
C——C 612
C———C, C——C, C—C
5. Draw Lewis structures to represent each of the following formulas:
a. NH3
b. H2O
c. CH4
d. C2H2
e. CH2O
O
H
HOC|Oa
HOC'COH
HOHOCOHO
H
HOO
O
H
F F FF
HONOH
O
H
F F
44 CHEMICAL BONDING MODERN CHEMISTRYCopyright © by Holt, Rinehart and Winston. All rights reserved.
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C H A P T E R 6 R E V I E W
Chemical Bonding
SECTION 3
SHORT ANSWER Answer the following questions in the space provided.
a1. The notation for sodium chloride, NaCl, stands for one
(a) formula unit. (c) crystal.(b) molecule. (d) atom.
d2. In a crystal of an ionic compound, each cation is surrounded by a number of
(a) molecules. (c) dipoles.(b) positive ions. (d) negative ions.
b3. Compared with the neutral atoms involved in the formation of an ionic compound, the crystal lattice that results is
(a) higher in potential energy. (c) equal in potential energy.(b) lower in potential energy. (d) unstable.
b4. The lattice energy of compound A is greater in magnitude than that of compound B. Whatcan be concluded from this fact?
(a) Compound A is not an ionic compound. (b) It will be more difficult to break the bonds in compound A than those in compound B. (c) Compound B has larger crystals than compound A.(d) Compound A has larger crystals than compound B.
b5. The forces of attraction between molecules in a molecular compound are generally
(a) stronger than the attractive forces among formula units in ionic bonding.(b) weaker than the attractive forces among formula units in ionic bonding.(c) approximately equal to the attractive forces among formula units in ionic bonding.(d) equal to zero.
6. Describe the force that holds two ions together in an ionic bond.
The force of attraction between unlike charges holds a negative ion and a positive
ion together in an ionic bond.
7. What type of energy best represents the strength of an ionic bond?
lattice energy
MODERN CHEMISTRY CHEMICAL BONDING 45Copyright © by Holt, Rinehart and Winston. All rights reserved.
Name Date Class
SECTION 3 continued
8. What types of bonds are present in an ionic compound that contains a polyatomic ion?
The atoms in a polyatomic ion are held together with covalent bonds, but
polyatomic ions combine with ions of opposite charge to form ionic compounds.
9. Arrange the ionic bonds in the table below in order of increasing strength from weakest tostrongest.
Ionic bond Lattice energy (kJ/mol)
NaCl �787
CaO �3384
KCl �715
MgO �3760
LiCl �861
KCl, NaCl, LiCl, CaO, MgO
10. Draw Lewis structures for the following polyatomic ions:
a. NH4�
b. SO42�
11. Draw the two resonance structures for the nitrite anion, NO2�.
N|O
aO Oa E
� NO|
aO OaE�A A
O
OSOO[ ]2–
O
C
CC O
C
CC
OCCC
O
C
CC
HO
HONOHO
H]
+
[
46 CHEMICAL BONDING MODERN CHEMISTRYCopyright © by Holt, Rinehart and Winston. All rights reserved.
Name Date Class
C H A P T E R 6 R E V I E W
Chemical Bonding
SECTION 4
SHORT ANSWER Answer the following questions in the space provided.
b1. In metals, the valence electrons are considered to be
(a) attached to particular positive ions. (c) immobile.(b) shared by all surrounding atoms. (d) involved in covalent bonds.
a2. The fact that metals are malleable and ionic crystals are brittle is bestexplained in terms of their
(a) chemical bonds. (c) enthalpies of vaporization.(b) London forces. (d) polarity.
d3. As light strikes the surface of a metal, the electrons in the electron sea
(a) allow the light to pass through.(b) become attached to particular positive ions.(c) fall to lower energy levels.(d) absorb and re-emit the light.
d4. Mobile electrons in the metallic bond are responsible for
(a) luster. (c) electrical conductivity.(b) thermal conductivity. (d) All of the above.
a5. In general, the strength of the metallic bond moving from left toright on any row of the periodic table.
(a) increases (c) remains the same(b) decreases (d) varies
c6. When a metal is drawn into a wire, the metallic bonds
(a) break easily. (c) do not break.(b) break with difficulty. (d) become ionic bonds.
7. Use the concept of electron configurations to explain why the number of valence electrons in metalstends to be less than the number in most nonmetals.
Most metals have their outer electrons in s orbitals, while nonmetals have their
outer electrons in p orbitals.
MODERN CHEMISTRY CHEMICAL BONDING 47Copyright © by Holt, Rinehart and Winston. All rights reserved.
Name Date Class
SECTION 4 continued
8. How does the behavior of electrons in metals contribute to the metal’s ability to conduct electricityand heat?
The mobility of electrons in a network of metal atoms contributes to the
metal’s ability to conduct electricity and heat.
9. What is the relationship between the enthalpy of vaporization of a metal and the strength of thebonds that hold the metal together?
The amount of energy required to vaporize a metal is a measure of the strength
of the bonds that hold the metal together. The greater a metal’s enthalpy of
vaporization, the stronger the metallic bond.
10. Draw two diagrams of a metallic bond. In the first diagram, draw a weak metallic bond; in thesecond, show a metallic bond that would be stronger. Be sure to include nuclear charge and numberof electrons in your illustrations.
a. b.
weak bond strong bond
Note: In the strong bond, the charge on the nucleus and the number of electronsmust be greater than in the weak bond.
11. Complete the following table:
Metals Ionic Compounds
Components atoms ions
Overall charge neutral neutral
Conductive in the solid state yes no
Melting point low to high high
Hardness soft to hard hard
Malleable yes no
Ductile yes no
���
��
�� ��
� � �
��
��
� �
��
�
�
�
�
48 CHEMICAL BONDING MODERN CHEMISTRYCopyright © by Holt, Rinehart and Winston. All rights reserved.
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C H A P T E R 6 R E V I E W
Chemical Bonding
SECTION 5
SHORT ANSWER Answer the following questions in the space provided.
1. Identify the major assumption of the VSEPR theory, which is used to predict the shape of atoms.
Pairs of valence electrons repel one another.
2. In water, two hydrogen atoms are bonded to one oxygen atom. Why isn’t water a linear molecule?
The electron pairs that are not involved in bonding also take up space, creating
a tetrahedron of electron pairs and making the water molecule angular or bent.
3. What orbitals combine together to form sp3 hybrid orbitals around a carbon atom?
the s orbital and all three p orbitals from the second energy level
4. What two factors determine whether or not a molecule is polar?
electronegativity difference and molecular geometry or unshared electron pairs
5. Arrange the following types of attractions in order of increasing strength, with 1 being the weakestand 4 the strongest.
3 hydrogen bonding
4 ionic
2 dipole-dipole
1 London dispersion
6. How are dipole-dipole attractions, London dispersion forces, and hydrogen bonding similar?
They are all forces of attraction between molecules. In all cases there is an attraction
between the slightly negatively-charged portion of one molecule and the slightly
positively charged portion of another molecule.
MODERN CHEMISTRY CHEMICAL BONDING 49Copyright © by Holt, Rinehart and Winston. All rights reserved.
Name Date Class
SECTION 5 continued
7. Complete the following table:
Formula Lewis structure Geometry Polar
H2S bent yes
CCl4 tetrahedral no
BF3 trigonal planar no
H2O bent yes
PCl5 trigonal bipyramidal no
BeF2 linear no
SF6 octahedral noCF C
S
—C CF CC
CF CC
——
——
—
CF CC
CF CC CF CC
CF C—Be—
C CF CC
P
—
CClCC
CCl
CCl
ClCCCla
a
a
—
—CC
——
OH
—C C—
H
B
—
—
—
F C
CFa CFa
C C
—C—
——
CClCC
CCl
CC CCl
CC
CClCC
SH
—
C C—
H
50 CHEMICAL BONDING MODERN CHEMISTRYCopyright © by Holt, Rinehart and Winston. All rights reserved.
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C H A P T E R 6 R E V I E W
Chemical Bonding
MIXED REVIEW
SHORT ANSWER Answer the following questions in the space provided.
1. Name the type of energy that is a measure of strength for each of the following types of bonds:
lattice energy a. ionic bond
bond energy b. covalent bond
enthalpy of vaporization c. metallic bond
2. Use the electronegativity values shown in Figure 20, on page 161 of the text, to determine whethereach of the following bonds is nonpolar covalent, polar covalent, or ionic.
ionic nonpolar covalenta. H—F d. H—H
ionic polar covalentb. Na—Cl e. H—C
polar covalent polar covalentc. H—O f. H—N
3. How is a hydrogen bond different from an ionic or covalent bond?
A hydrogen bond is a dipole-dipole attraction between a partially positive hydrogen
atom and the unshared electron pair of a strongly electronegative atom such as O,
N, or F. Unlike ionic or covalent bonds, in which electrons are given up or shared,
the hydrogen bond is a weaker attraction. Hydrogen bonds are generally
intermolecular, while ionic and covalent bonds occur between ions or atoms
respectively.
4. H2S and H2O have similar structures and their central atoms belong to the same group. Yet H2S is agas at room temperature and H2O is a liquid. Use bonding principles to explain why this is.
Oxygen has higher electronegativity than sulfur, which creates a highly polar bond.
Increased polarity in H2O bonds means a stronger intermolecular attraction, making
water a liquid at room temperature. Hydrogen bonding exists between water
molecules, but not between hydrogen sulfide molecules.
MODERN CHEMISTRY CHEMICAL BONDING 51Copyright © by Holt, Rinehart and Winston. All rights reserved.
Name Date Class
MIXED REVIEW continued
5. In what way is a polar-covalent bond similar to an ionic bond?
There is a difference between the electronegativities of the two atoms in both
types of bonds that results in electrons being more closely associated with the
more electronegative atom.
6. Draw a Lewis structure for each of the following formulas. Determine whether the molecule ispolar or nonpolar.
polar a. H2S
polar b. COCl2
polar c. PCl3
polar d. CH2O
—
H
— OH aC
——
—P—
—CCCl
CC CCl
CC
CClCC
C—
CCl
CC
CCl
CC
—OCC
——
SH
—
C C—
H
52 CHEMICAL BONDING MODERN CHEMISTRYCopyright © by Holt, Rinehart and Winston. All rights reserved.
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