Chapter 2: Chemical Compounds and Bonding
Section 2.1: Ionic Compounds, pages 22–23
1. An ionic compound combines a metal and a non-metal joined together by an ionic bond.
2. An electrostatic force holds the positive and negative ions in an ionic bond together.
3. a
4. True
5. (a) Formation of potassium bromide:
(b) Formation of calcium chloride:
6. There is no such thing as a single molecule of sodium chloride because sodium chloride is an ionic
compound. The smallest subunit of sodium chloride is the formula unit, which consists of many repeating
patterns of sodium and chloride. The reason that single molecules of the compound do not exist is that the
properties of sodium chloride do not emerge unless many subunits of the pattern exist together in a crystalline
structure. For example, the hardness of sodium chloride emerges from the ionic bonds that join each ion to
many other ions of the opposite charge, not just a single ion to another ion.
7. Figure 1
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Chapter 2: Chemical Compounds and Bonding
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8. Table 1 Properties of Ionic Compounds
Property
Cause
Explanation
hardness
ionic bonds
Ionic bonds are quite rigid and resist being stretched. This
gives ionic compounds a hard texture.
high melting
electrostatic forces
The electrostatic force between positive and negative ions that
temperature
holds ionic compounds together is extremely strong and
requires a lot of energy to break.
crystal
regular ion
Ionic compounds form crystalline structures because positive
structure
arrangement
and negative ions are held tightly and rigidly at regular
angles, which creates lattice structure.
form
water molecules
When placed in water, polar water molecules surround the
electrolytes
ions and separate them from one another, causing electrolytes
to form.
conductivity
ion separation
When dissolved and broken up into ions, the ions themselves
are charged particles. These charged particles are capable of
conducting electricity.
Section 2.2: Molecular Elements and Compounds, pages 24–26
1. False. Unlike ionic compounds, the smallest subunit of a molecular compound is a single molecule.
2. a
3. Molecular compounds are usually made up of atoms that are non-metal, while ionic compounds include both
metals and non-metals.
4. Unlike ionic compounds, most molecular compounds usually have low melting points and have low
solubility in water.
5. (a) A formula for finding the bonding capacity of an element, given the number of electrons in its valence
shell, is as follows: If V is the number of electrons in the valence shell and B stands for bonding capacity, the
formula is B = 8 –V. For example, using sulfur and chlorine:
BS = 8 ! V
=8–6
=2
BCl = 8 ! V
and
=8–7
=1
6. A lone pair is a pair of electrons that is not involved in covalent bonding.
7. b
8. Covalent bonds result from the sharing of a pair of electrons by two. In an ionic bond, electrons are
transferred from one atom to another, forming a positive ion and a negative ion, which are held together by
electrostatic force.
9. Lewis structure and structural formula for carbon dioxide, CO2:
Step 1. Arrange the symbols.
Step 2. Count the valence electrons.
1 C atom: 4 e–
2 O atoms: 12 e–
Total: 16 e–
Step 3. Use Lewis dots to make single covalent bonds. Place lone pairs to satisfy the octet rule for surrounding
atoms.
Step 4. Place remaining electrons on the central atom. All 16 electrons have been used, so none remain.
Step 5. Reposition electrons to give all atoms in the compound a full octet.
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Chapter 2: Chemical Compounds and Bonding
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Step 6. Replace shared pairs with single or multiple covalent bonds to make a Lewis structure. Remove any
lone pairs to make a structural formula.
10. Lewis structure and structural formula for the phosphate ion, PO43–.
Step 1. Arrange the symbols.
Step 2. Count the electrons.
1 P atom: 5 e–
4 O atoms: 24 e–
–3 charge of PO43–: 3 e–
Total: 32 e–
Step 3. Use Lewis dots to make single covalent bonds.
Step 4. Place lone pairs to satisfy the octet rule for surrounding atoms.
Step 5. Compare electrons used to total number of electrons. All 32 electrons have been used, so none remain.
The central atom has a full octet.
Step 6. Replace the central dots with covalent bonds. Check the finished structure to make sure all atoms have
a full octet. Add brackets and a charge. Eliminate lone pairs to form a structural formula.
11.
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Chapter 2: Chemical Compounds and Bonding
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Section 2.3: Chemical Bonding and Electronegativity, pages 27–28
1. False. As the atomic radius of an atom decreases, electronegativity increases.
2. Within a single row of the periodic table, the element farthest to the right side will have the greatest
electronegativity.
3. a
4. Table 1 Electronegativity Trends
Low electronegativity
High electronegativity
large atomic radius
X
large ionic radius
X
high first ionization energy
X
location toward left side of periodic table
X
location toward right side of periodic table
X
location toward upper part of periodic table
X
electron affinity
X
metal
X
forms diatomic molecules
X
5. c
6. No, it is not possible for a diatomic molecule to have a polar-covalent bond. By definition, a diatomic
molecule consists of two atoms with the exact same electronegativity value. Therefore, the ΔEN for a diatomic
molecule is always zero, so the bond is always non-polar covalent.
7. (a) A compound consisting of two different atoms that have an electronegativity difference of 1.4 is held
together by a polar-covalent bond, because its ΔEN is greater than 0 and less than 1.7.
(b) This compound would be highly polar. It would be more polar, for example, than the quite polar O–H bond
that exists in water.
8. Table 2 Covalent, Polar-Covalent, and Ionic Compounds
Covalent
Polar-covalent Ionic
compound
compound
compound
0
>
0
and
<
1.7
≥ 1.7
ΔEN
example
N2
MgCl
NaF
atom with greater electronegativity
neither
Cl
F
“tug-of-war” winner
neither
Cl
F
9. The methanol molecule is more likely to be more polar than the methane molecule. The methane molecule
has all fairly non-polar C–H bonds, so it is likely to be less polar than the methanol molecule, which is
asymmetric and includes a fairly polar O–H bond, with a ΔEN of 1.4.
Section 2.4: Chemical Formulas and Nomenclature, pages 29–30
1. An ionic compound that is composed of exactly two different ions is called a binary ionic compound.
2. False. All compounds with a common name also have an IUPAC name.
3. b
4. In the ionic compound X2(YZ4)5, if the polyatomic ion YZ4 has a charge of –2, the X ion has a charge of +5.
5. (a) Chemical formula for calcium nitride:
Step 1. Write the symbols of the elements with the metal first and the non-metal second.
Ca
N
Step 2. Write the charges above the symbols.
+2
Ca
–3
N
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Chapter 2: Chemical Compounds and Bonding
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Step 3. Determine how many of each type of ion are required to bring the total charge
to zero.
3(+2) + 2(–3) = 0
Ca
N
Step 4. Write the chemical formula with subscripts.
Ca3N2.
Step 5. Make sure that the subscripts are a lowest whole number ratio.
The chemical formula for calcium nitride is Ca3 N2.
(b) Chemical formula for magnesium nitrate:
Step 1. Write the symbols of the elements with the metal first and the polyatomic ion second.
Mg
NO3–
Step 2. Write the charges above the symbols.
+2
Mg
–1
NO 3
Step 3. Determine how many of each type of ion are required to bring the total charge
to zero.
1(+2) + 2(–1) = 0
Mg
NO 3
Step 4. Write the chemical formula with subscripts.
Mg1(NO3)2
Step 5. Make sure that the subscripts are a lowest whole number ratio. Omit the subscript “1.”
The chemical formula for magnesium nitrate is Mg(NO3)2
6. (a) The IUPAC name for CaFl2 is calcium fluoride.
(b) The IUPAC name for Al2O3 is aluminum oxide.
(c) The IUPAC name for Na2S is sodium sulfide.
(d) The IUPAC name for ZnI2 is zinc iodide.
7. The IUPAC name for Pb3(PO4)2:
Step 1. This compound contains lead, Pb, which is a multivalent metal that can have a charge of +2 or +4, and
phosphate, PO4, a polyatomic ion that has a charge of –3.
Step 2. Write the chemical formula with the charge of the anion above its symbol.
–3
Pb3 (PO 4 ) 2
Step 3. The charge on the Pb ion may be +2 or +4.
Step 4. There are 2 phosphate ions, each with a –3 charge. Total negative charge = –6
Step 5. The total positive charge is +6, by the zero-sum rule. This charge is shared between three lead ions, so
the charge on each Pb ion is +2.
Step 6. The name of Pb3(PO4)2 is lead(II) phosphate.
8. (a) The IUPAC name of CuCl2:
Step 1. This compound contains copper, Cu, which is a multivalent metal that can have a charge of +1 or +2.
Step 2. Write the chemical formula with the charge of the anion above its symbol.
–1
CuCl2
Step 3. The charge on the Cu ion may be +1 or +2.
Step 4. There are 2 chloride ions, each with a –1 charge. Total negative charge = –2
Step 5. The total positive charge is +2, , by the zero-sum rule, so the charge on the copper ion is +2.
Step 6. The name of CuCl2 is copper(II) chloride.
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Chapter 2: Chemical Compounds and Bonding
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(b) The IUPAC name of FeBr2:
Step 1. This compound contains iron, Fe, which is a multivalent metal that can have a charge of +2 or +3.
Step 2. Write the chemical formula with the charge of the anion above its symbol.
–1
FeBr2
Step 3. The charge on the Fe ion may be +2 or +3.
Step 4. There are 2 bromide ions, each with a –1 charge. Total negative charge = –2
Step 5. The total positive charge is +2, , by the zero-sum rule, so the charge on the iron ion is +2.
Step 6. The name of FeBr2 is iron(II) bromide.
(c) The IUPAC name of FeCl3:
Step 1. This compound contains iron, Fe, which is a multivalent metal that can have a charge of +2 or +3.
Step 2. Write the chemical formula with the charge of the anion above its symbol.
–1
FeCl3
Step 3. The charge on the Fe ion may be +2 or +3.
Step 4. There are 3 chloride ions, each with a –1 charge. Total negative charge = –3
Step 5. The total positive charge is +3, , by the zero-sum rule, so the charge on the iron ion is +3.
Step 6. The name of FeCl3 is iron(III) chloride.
(d) The IUPAC name of PbBr4:
Step 1. This compound contains lead, Pb, which is a multivalent metal that can have a charge of +2 or +4.
Step 2. Write the chemical formula with the charge of the anion above its symbol.
–1
PbBr4
Step 3. The charge on the Fe ion may be +2 or +4.
Step 4. There are 4 bromide ions, each with a –1 charge. Total negative charge = –4
Step 5. The total positive charge is +4, , by the zero-sum rule, so the charge on the lead ion is +4.
Step 6. The name of PbBr4 is lead(IV) bromide.
9. (a) Name of N2O5: Does the formula begin with H? No. → Are the bonds covalent (ΔEN < 1.7)? Yes. ΔEN
for O–N = 3.4 – 3.0 = 0.4 < 1.7, so the bonds are covalent. → It is a molecular substance. Are all the elements
the same? No. → It is a molecular compound. Name each element with the proper prefix: The compound is
dinitrogen pentoxide.
(b) Name of CuF2: Does the formula begin with H? No. → Are the bonds covalent (ΔEN < 1.7)? No. ΔEN for
F–Cu = 4.0 – 1.9 = 2.1 > 1.7, so the bonds are not covalent. → It is an ionic compound. Does the chemical
formula begin with a multivalent metal ion? Yes. → Name the first element followed by its charge as a Roman
numeral: copper(II). → Does the formula contain a polyatomic ion? No. → Does the formula contain H2O?
No. → It is a binary ionic compound. Name the ions in the order in which they appear in the chemical formula:
The compound is copper(II) fluoride.
(c) Name of Al(NO3)3: Does the formula begin with H? No. → Are the bonds covalent (ΔEN < 1.7)? No. → It
is an ionic compound. Does the chemical formula begin with a multivalent metal ion? No. → Does the formula
contain a polyatomic ion? Yes. → Does the formula contain H2O? No. → It is a polyatomic ionic compound.
Name the ions in the order in which they appear in the chemical formula: The compound is aluminum nitrate.
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Chapter 2: Chemical Compounds and Bonding
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Section 2.5: Explore an Issue in Chemical Compounds: Sugar versus Artificial
Sweeteners, page 31
1. Sugars have no nutritional value other than as a source of energy for the body.
2. False. A sucrose molecule is made of one molecule of glucose joined with one molecule of fructose.
3. a
4. (a) Sucralose is 600 times as sweet as sugar.
(b) To get the same level of sweetness in a 1 L pitcher of ice tea as with 100 g of sucrose, you would need to
add only 0.17 g of sucralose (100 ÷ 600 = 0.17).
(c) Even though some artificial sweeteners have more calories per gram than sugar, they are called “lowcalorie” sweeteners because you use such a small amount of them to sweeten a food item that the amount you
take in has only a few calories.
5. Table 1 Sweeteners
Sweetener Sweetness (1–10)
Health benefits
Health risk
sucrose
3
energy, not carcinogenic
obesity, diabetes, other problems
fructose
4
energy, not carcinogenic
obesity, diabetes, other problems
sucralose
10
unsafe only at high doses
aspartame
9
few calories, less risk of obesity
and diabetes
few calories, less risk of obesity
and diabetes
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breakdown products can cause
problems
Chapter 2: Chemical Compounds and Bonding
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Chapter 2 Summary, page 32
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Chapter 2: Chemical Compounds and Bonding
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Chapter 2 Questions, pages 33–34
1. False. The smallest unit of an ionic compound is the formula unit.
2. c
3. Table 1 Properties of Ionic Compounds
Typical ionic
Property
Reason
compound
texture
very hard, brittle,
breaks easily
melting point
very high
solubility in
water
very soluble
electrical
conduction
none in solid state;
good in liquid state
and when dissolved
Ionic bonds resist stretching. The crystal lattice structure is
easily offset if the crystal is struck. Ions with the same charge
are suddenly side by side and repel one another; the crystal
cracks.
Electrostatic forces (ionic bonds) are very strong and resist
breaking.
Polar water molecules are able to wedge in between charged
ions, causing the compound to break up, or dissolve, releasing
free-floating ions into the solution.
Ions are charged so they are good carriers of electricity.
4. Figure 1
5. Formation of lithium oxide:
6. Lewis structure and structural formula for SCl2:
7. If in the ionic compound X4Y3, the X cation has a charge of 3+, the Y anion has a charge of –4.
8. (a) The IUPAC name for K2S is potassium sulfide.
(b) The IUPAC name for Hg3(PO4)2 is mercury(II) phosphate.
9. (a) The chemical formula for zinc chromate is ZnCrO4.
(b) The chemical formula for lead(IV) bromide is PbBr4.
10. The acetic acid molecule is more likely to dissolve in water than the ethane molecule. The ethane molecule
has all fairly non-polar C–H bonds, so it is likely to be less polar than the acetic acid, which has two polar C–O
bonds. Since polar molecules are usually more soluble in water than non-polar molecules, you would expect
acetic acid to be more soluble.
11. If you add half the normal amount of sweetener to a bottle of pop, and your sweetener is a compound that
is half sucrose and half aspartame, the compound is likely to be extremely unsuccessful. Aspartame is
180 times as sweet as sucrose, so the pop will be sickeningly sweet.
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