Answers to book problems
Page 177
1. Ionic bonding involves losing and gaining electrons to form ions and involves the attraction between large
numbers of + and – ions. There are no individual molecules in ionic compounds. Covalent bonding involves
sharing electron pairs between atoms.
2. A large difference in electronegativity between two atoms causes the bonding to be ionic. A small difference in
electronegativity between two atoms causes the bonding to be covalent (molecular).
3. A. ionic
b. polar-covalent
c. polar-covalent
4. I and Br, Cu and S, Li and F
5.
a. CuCl has the greater % ionic character because it has the greater difference in electronegativity
b. The chlorine in CuCl has the greater negative partial charge compared to the chlorine in ICl because
there is a greater difference in electronegativity, so the electrons in the CuCl bond get pulled more
toward the Cl in CuCl than they do toward the Cl in ICl
Page 209
3. The greater the electronegativity difference between two atoms is, the more ionic the bond between them is.
4. a. Polar refers to bonds that have an uneven distribution of charge. In other words, the shared electrons in the bond
are attracted more to one side than the other.
b. In a polar-covalent bond the electron pair is not shared equally by the two bonded atoms. (The electrons are closer to
one atom than the other.) In a nonpolar-covalent bond, the electron pair is shared equally between the two bonded
atoms.
5. Atoms form chemical bonds if it lowers their potential energy. In other words, they bond if it makes them more
stable.
6.
Electronegativity
(from page 161)
H 2.1
S 2.5
K 0.8
Si 1.8
K 0.8
Se 2.4
C 2.5
Electronegativity
(from page 161)
I 2.5
O 3.5
Br 2.8
Cl 3.0
Cl 3.0
S 2.5
H 2.1
Difference
0.4
1.0
2.0
1.2
2.2
0.1
0.4
Probable Bond Type
(see page 176)
Polar-covalent
Polar-covalent
ionic
Polar covalent
ionic
Nonpolar-covalent
Polar-covalent
7. The pairs above listed from most ionic to most covalent:
K and Cl, K and Br, Si and Cl, S and O, tie between H and I and C and H, Se and S
Which atom is more
electronegative?
I
O
Br
Cl
Cl
S
C
Page 194, #4. B is molecular, A is ionic. The intermolecular attractions that hold molecules together are weaker than
the attraction between ions in an ionic compound. This causes lower melting and boiling points in molecular
substances.
Answers to book assignment for “Intermolecular Forces”
Page 207
5. Hydrogen bonding is responsible for water’s high boiling point. In general, boiling point is a measure of the amount of
energy needed to overcome intermolecular attractions. Hydrogen bonding is a particularly strong dipole-dipole
attraction that causes a powerful attraction between water molecules. This causes water to have a high boiling point.
6. Boiling point is directly correlated with the strength of intermolecular forces. The boiling point is the temperature at
which a molecule goes from a liquid state to a gas state. In the gaseous state, all the intermolecular forces are
essentially broken. The stronger the intermolecular forces, the more energy needed to break the intermolecular
forces, the higher the boiling point.
Page 211
37.
a. Intermolecular forces are the forces of attraction between molecules.
b. Intermolecular forces are weaker than the forces involved in ionic and metallic bonding.
c. The strongest intermolecular forces occur between polar molecules.
38. The larger the difference in electronegativities of the atoms in the bond, the greater the polarity of that bond.
39.
a. Dipole-dipole forces are the forces of attraction between polar molecules.
b. The overall polarity of a molecule depends on the polarity of the individual bonds and the geometry of the
molecule. For example, the C-H bonds in methane are polar bonds, but methane as a whole molecule is nonpolar due to its symmetrical geometry.
40.
a. An induced dipole is an instantaneous dipole that is produced in a nonpolar molecule when the molecule’s
electrons are momentarily attracted by a polar molecule.
b. Induced dipoles account tor the solubility of nonpolar compounds, such as oxygen, in polar compounds, such
as water.
41.
a. Hydrogen bonding is a particularly strong dipole-dipole force that occurs between molecules containing
hydrogen atoms and highly electronegative atoms, such as those of N, O, and F.
b. Because of the large electronegativity difference between H and F,N, and O, the bonding within molecules
containing these atoms is extremely polar. This causes very strong intermolecular forces between these highly
polar molecules.
42. London dispersion forces are the weakest of intermolecular forces caused by momentary, induced dipoles created
in nonpolar molecules and atoms.
45. a. toward F
b. toward Cl
c. toward Br
d. toward I
46. a. nonpolar
b. polar
c. polar
d. nonpolar
47. a. polar
b. nonpolar
c. nonpolar
50.
d,c,a,b
52.
a. metals and nonmetals
d. polar
e. polar
f. polar
e. nonpolar
b. nonmetals only
c. metals only
63.
Electronegativity
(page 161)
Zn 1.6
Br 2.8
S 2.5
Electronegativity
(page 161)
O 3.5
I 2.5
Cl 3.0
Difference
1.9
0.3
0.5
Bond Type (Page
176)
ionic
Polar-covalent
Polar-covalent
More-negative
atom
O
Br
Cl
64.
69. F has the highest electronegativity and therefore has the greatest attraction for the electrons it shares in a covalent
bond. In other words, it pulls the electrons it shares with other atoms more strongly toward itself.
70.
a. Hydrogen can’t be a central atom because in can only form one bond. Also, there are too many valence
electrons.
b. The carbon and oxygen atoms have more than 8 electrons around them.
c. The top chlorine atom has too many electrons.
The correct structures are shown below.
71. Because of its symmetry, methane is nonpolar, so the only forces holding one methane molecule to another would
be the weak London forces. In contrast, ammonia molecules are highly polar so the attraction between NH3 molecules
is much stronger. Therefore, it takes more energy to separate ammonia molecules so that they become a gas.