Name ____________________________________________
Date ____________________
Class ___________________
8
Covalent Bonding
Reviewing Vocabulary
Match the definition in Column A with the term in Column B.
Column A
Column B
______
1. The tendency of an atom in a compound to attract electrons
a. structural formula
______
2. A kind of bond in which there is unequal sharing of electrons
b. molecule
______
3. Any bond in which there is electron sharing
c. VSEPR model
______
4. The particle formed when two or more atoms bond covalently
d. coordinate covalent bond
______
5. Reactions that occur when more energy is released forming new
bonds than is required to break bonds in the initial reactants
e. hybridization
______
6. A kind of bond in which electrons are shared in an area centered
between the two atoms
g. electronegativity
______
7. A kind of bond formed by overlap of parallel orbitals
h. sigma bond
______
8. Any acidic compound that contains oxygen
i. polar covalent
______
9. A model that shows how the atoms are arranged in a molecule
j. pi bond
______ 10. Reactions that occur when more energy is required to break existing
bonds in reactants than is released when new bonds form in the
product molecules
______ 11. A condition that occurs when more than one valid Lewis structure
can be drawn for a molecule
f. oxyacid
k. covalent bond
l. resonance
m. endothermic
n. exothermic
______ 12. A kind of bond in which one of the atoms provides both electrons
for sharing
______ 13. A model used to determine molecular shape
______ 14. The combining of orbitals in an atom to form new, identical orbitals
Chemistry: Matter and Change
1
Chapter Assessment
Name ____________________________________________
Date ____________________
Class ___________________
8
Understanding Main Ideas (Part A)
Circle the letter of the choice that best completes the statement or answers the question.
1. In the formation of a covalent bond, electrons are
a. shared.
b. lost.
c. gained.
d. transferred.
2. Which of the following elements normally exists in the form of diatomic molecules?
a. helium
b. argon
c. iron
d. nitrogen
3. Four electrons are shared in a
a. single covalent bond.
b. double covalent bond.
c. triple covalent bond.
d. quadruple covalent bond.
4. Which of the following molecules contains only sigma bonds?
a. methane
b. oxygen
c. carbon dioxide
d. nitrogen
5. Which of the following molecules contains a triple bond?
a. methane
b. oxygen
c. carbon dioxide
d. nitrogen
6. How many pi bonds are there in a triple bond?
a. none
b. one
d. three
c. two
7. Which of the following molecules would be expected to have the greatest bond dissociation energy?
a. F2
b. O2
c. N2
d. Cl2
In the space at the left, write true if the statement is true; if the statement is false, change the
italicized term to make it true.
___________________ 8. In a chemical name, the prefix used to indicate the presence of
two atoms of a given kind is bi-.
___________________ 9. The prefix hydro- is used in naming binary acids.
___________________ 10. The oxyacid suffix for an acid that contains an anion ending
in -ate is -ic.
___________________ 11. In Lewis structures, hydrogen is always a terminal atom.
___________________ 12. In the carbon dioxide molecule, the central atom is a carbon atom.
___________________ 13. In the compound BH3, the boron atom has more than an octet of
electrons.
___________________ 14. The VSEPR model is based on the idea that in a molecule, nuclei
repel each other as much as possible.
Chemistry: Matter and Change
2
Chapter Assessment
Name ____________________________________________
Date ____________________
Class ___________________
8
Understanding Main Ideas (Part B)
The diagram below represents different hybridizations of the orbitals of three carbon
atoms, labeled X, Y, and Z. Use the diagram to answer the questions that follow.
1. Write the electron configuration of an unbonded carbon atom (atomic number 6) before
hybridization occurs.
______________________________________________________________________________________________
2. Look at carbon atom X in the diagram. What is the symbol for the hybrid orbitals formed by carbon
atom X? How many of them are there in that atom?
______________________________________________________________________________________________
3. Does carbon atom X have any unhybridized orbitals? If so, tell how many and write the symbol for
them.
______________________________________________________________________________________________
4. To how many other atoms would carbon atom X be attached? What types of bonds— single, double,
or triple—would they be? State whether each attachment would involve sigma bonds, pi bonds, or
both.
______________________________________________________________________________________________
5. What would be the shape of the molecule formed by carbon atom X when it bonds in that way?
______________________________________________________________________________________________
6. Suppose that the attachments in that molecule are to atoms of the same kind with an electronegativity
greater than that of carbon. Would each bond be polar or nonpolar? Would the molecule as a whole
be polar or nonpolar? Explain.
______________________________________________________________________________________________
______________________________________________________________________________________________
7. Look at carbon atom Y in the diagram. What is the symbol for the hybrid orbitals formed by carbon
atom Y? How many of them are there in that atom?
______________________________________________________________________________________________
Chemistry: Matter and Change
3
Chapter Assessment
Name ____________________________________________
Date ____________________
Class ___________________
8
Thinking Critically
The graph shows the electronegativities of the elements of periods 2 and 3 of the periodic table,
except for the noble gases. Use the graph to answer the following questions.
1. If two atoms of differing electronegativity are bonded covalently to each other, what is true of the
electrons they share? What type of bond results in such a case?
______________________________________________________________________________________________
______________________________________________________________________________________________
2. How does the electronegativity of boron (B) compare with that of nitrogen (N)? In terms of the
periodic table, how are these two elements related? Compare aluminum (Al) with phosphorus (P) in
the same way.
______________________________________________________________________________________________
______________________________________________________________________________________________
3. Describe the trend in electronegativity illustrated for period-2 and period-3 elements.
______________________________________________________________________________________________
4. How does the electronegativity of boron (B) compare with that of aluminum (Al)? In terms of the
periodic table, how are these two elements related? Compare nitrogen (N) with phosphorus (P) in the
same way.
______________________________________________________________________________________________
______________________________________________________________________________________________
5. Describe the trend in electronegativity within a group of the periodic table, as suggested by the
graph.
______________________________________________________________________________________________
Chemistry: Matter and Change
4
Chapter Assessment
Name ____________________________________________
Date ____________________
Class ___________________
8
Applying Scientific Methods
A college chemistry student is studying the properties of four unknown compounds, W, X, Y, and Z. She
has been informed that one of them is ionic and that the other three are covalent. Of the latter, she has
been told that the attractions between the formula units are dispersion forces in one case, hydrogen bonds
in another, and covalent (network) bonds in another. She has been asked to determine the type of
attractions for each substance. In an attempt to do so, she carries out experiments that reveal information
about the substances’ properties. Use this information to answer the questions that follow.
Property
Unknown W
Unknown X
Unknown Y
Unknown Z
Hardness of solid
soft
soft
brittle
brittle
Melting point (°C)
10
200
1500
3000
Boiling point (°C)
120
150
2500
4500
very soluble
insoluble
very soluble
insoluble
insoluble
very soluble
insoluble
insoluble
Conductivity of solid
nonconducting
nonconducting
nonconducting
nonconducting
Conductivity of liquid
nonconducting
nonconducting
conducting
nonconducting
Solubility in polar solvent
Solubility in nonpolar solvent
1. On the basis of the results of her hardness test, the student concludes that unknowns W and X are
covalent substances, and that either Y or Z is the ionic substance. Comment on the soundness of her
conclusion, given only the hardness information.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
2. The student examines the melting-point data, but claims that it is not useful in determining the
substances’ types of attractions. How would you reply to that claim?
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
3. On the basis of the results of the boiling-point and melting-point tests, the student concludes that W
is the hydrogen-bonded substance and that X must therefore be the substance that has the dispersion
forces. Is that conclusion valid? Explain.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
Chemistry: Matter and Change
5
Chapter Assessment
Name ____________________________________________
Date ____________________
Class ___________________
8
Applying Scientific Methods, continued
4. On the basis of the results of her solubility test, the student concludes that X must be covalent.
Comment, and state any further conclusions that can be derived about the other substances.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
5. On the basis of her electrical conductivity test, the student states that there must be some error
because unknown Y acts like a covalent substance when solid but like an ionic substance when
melted. Comment on her statement.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
6. The student examines the entire set of data but is unable to come to final, definite conclusions about
the substances’ types of attractions. Is it possible to do so, given the data? Explain, and state your
own conclusions if any.
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
7. How do the overall procedure and your reasoning illustrate scientific methods?
______________________________________________________________________________________________
______________________________________________________________________________________________
______________________________________________________________________________________________
Chemistry: Matter and Change
6
Chapter Assessment
TEACHER GUIDE AND ANSWERS
6. The bonds would be polar, but the molecule as a
Chapter Assessment - Chapter 8
whole would be nonpolar because of its shape and the
fact that the polarities would “cancel” one another.
7. sp2; three
Reviewing Vocabulary
1. g
2. i
Thinking Critically
3. k
1. The electrons are not shared equally, but are more
4. b
5. n
6. h
2.
7. j
8. f
9. a
3.
10. m
11. l
4.
12. d
13. c
14. e
5.
attracted to the more electronegative atom. The bond
is polar covalent.
N is more electronegative than B. Both are in period
2, with N to the right of B. P is more electronegative
than Al. Both are in period 3, with P to the right of
Al.
Electronegativity increases from left to right across
both periods.
B is more electronegative than Al. Both are in group
13, with B above Al. N is more electronegative than
P. Both are in group 15, with N above P.
Electronegativity decreases going down a group in
the periodic table.
Understanding Main Ideas (Part A)
Applying Scientific Methods
1. a
1. The conclusion is sound. Only covalent substances
2. d
are soft, although some covalent substances (network
solids) are hard and brittle. Ionic solids also are
brittle, so there is no way to tell whether Y or Z is the
ionic substance.
2. The claim is not valid. The low melting points of W
and X strongly suggest that they are covalent
molecular substances. The high melting points of Y
and Z suggest that one must be ionic, the other
covalent network, with Z more likely to be the
network solid.
3. The conclusion is valid. Hydrogen-bonded substances
have relatively high boiling points for molecular
substances, and that is true of X. Because Y has very
low melting and boiling points, and the remaining
unknowns do not, it must be the substance that has
the very weak dispersion forces.
4. The student’s conclusion is valid because only
nonpolar covalent substances are highly soluble in
nonpolar solvents. The high solubility of W and Y in
the polar solvent suggests that one is the ionic
substance and the other the hydrogen-bonded (highly
polar) one, but more information would be needed to
derive further conclusions.
3. b
4. a
5. d
6. c
7. c
8. di9. true
10. true
11. true
12. true
13. less
14. electrons
Understanding Main Ideas (Part B)
1. 1s22s22p2
2. sp3; four
3. It has no unhybridized orbitals.
4. four other atoms; four single bonds, each sigma only
5. tetrahedral
Chemistry: Matter and Change
7
Teacher Guide and Answers
TEACHER GUIDE AND ANSWERS
5. The statement is not valid. The two pieces of
information together suggest that Y is ionic because
ionic substances conduct when in the liquid state, but
not when in the solid state.
6. The entire set of data does allow identification of
each substance’s type of attractions. W must be
hydrogen-bonded covalent because of its relatively
high boiling point for a covalent molecular compound
and its solubility in the polar solvent. The fact that it
does not conduct as liquid and that its melting point is
not very high allows one to rule out that it is ionic. X
must be covalent with inter-molecular dispersion
forces because of its very low melting and boiling
points, lack of conductivity, and solubility in the
nonpolar solvent. Y must be ionic because of its high
melting and boiling points coupled with its
conductivity as liquid and its solubility in the polar
solvent. Z must be the covalent network solid. Its
very high melting and boiling points, brittleness, and
lack of conductivity support that conclusion.
7. The steps involve those often used in investigating a
problem scientifically. A question was initially posed,
experiments planned and carried out, observations
made, data analyzed, and conclusions reached on the
basis of the data.
Chemistry: Matter and Change
8
Teacher Guide and Answers