▲
▲
Fire dancing is a dangerous
art in which performers
manipulate burning
objects to create beautiful,
rhythmic patterns. The fire
is the main attraction in
the performance; it’s the
ever-changing movement
of light that keeps watchers
mesmerized. The dancer herself
is like a puppeteer who remains
obscured while creating the
effects. She does this not just by
controlling her movements but by
choosing the tools and fuel that
support the flames. In this way,
she controls the chemical reaction
that produces the light. Like all
chemical reactions, the one you see
here proceeds according to wellunderstood patterns determined
by the substances involved and the
conditions under which it occurs.
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Unit Contents
3
Chemical Names, Formulas,
and Equations
3.1 Ionic and Molecular
Compounds
3.2 Names and Formulas of Ionic
and Molecular Compounds
3.3 Chemical Equations and the
Law of Conservation of Mass
4
Classifying Compounds and
Chemical Reactions
4.1 Types of Chemical Reactions
4.2 Acids and Bases
4.3 Rates of Chemical Reactions
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What You Should Recall About...Physical and Chemical Properties
•
•
•
•
•
•
•
Properties of matter can be either physical or
chemical.
Physical properties are properties that do not
involve the way in which substances interact
chemically with other substances.
Chemical properties describe how substances
can change when they interact with other
substances to form new substances with new
properties.
Properties of matter can be either qualitative
or quantitative.
A qualitative property can be described
using words, such as “soft” and “red”; a
quantitative property can be described using a
measurement, for example, 100°C.
Examples of qualitative physical properties
include odour, colour, texture, state, and
malleability (the ability to be bent or
hammered without breaking).
Examples of quantitative physical properties
include melting point, boiling point,
solubility, and density.
Solubility describes how much of a
substance dissolves in another substance.
Check What You Recall
1. Window glass has a smooth texture. Brick
has a rough texture. Are these examples of
a physical property or a chemical property?
Explain your answer.
94
•
•
•
You can describe substances using their
physical properties just by observing them,
but chemical properties can only be observed
when substances interact in a chemical
change.
Some examples of chemical properties include
reactivity with other substances, such as water,
oxygen, or acids; and combustibility, the
ability of a substance to catch fire and burn
in air. Stability is another chemical property,
which refers to how easily the substance
breaks down to form other compounds.
Some examples of evidence that a chemical
change has taken place include the following:
• the formation of bubbles of gas when
baking powder and vinegar react
• the change in colour of a pair of blue jeans
that have been exposed to bleach
• the formation of a precipitate, such as the
formation of soap scum when soap and
minerals and water react, shown below
• the light and heat produced from a
campfire
• the sound of fireworks
Soap scum forms when soluble soap and soluble minerals in
water react to form a substance that does not dissolve in water.
2. Identify the types of properties described
in this sentence, and give reasons for your
choice: “Beeswax is soft and burns with a
bright flame.”
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3. Decide whether each statement below
describes a physical property or a chemical
property of a substance. Then indicate
whether it is a qualitative property or a
quantitative property.
(a) It is a pale yellow gas at room
temperature.
(b) It can burn or etch glass permanently.
(c) Its density is 1.695 g/L.
(d) It explodes when it reacts with water.
(e) Its melting point is 0°C.
4. Which chemical property of propane would
be most important to keep in mind when
using a gas barbecue? Explain your answer.
5. Tetrafluoromethane is a compound that is
a potent greenhouse gas. It lasts for a long
time in the atmosphere because it does
not readily break down or react with other
substances. What chemical properties of
tetrafluoromethane are described here?
What You Should Recall About...Classifying Matter
•
•
•
•
Matter can be classified according to whether
it is a pure substance or a mixture.
According to the particle theory of matter,
pure substances contain only one type of
particle. They cannot be separated into other
substances by physical means.
According to the particle theory of matter,
mixtures contain more than one type of
particle. They can be separated into pure
substances by physical means.
Pure substances are either elements or
compounds. Elements cannot be broken
down further by physical or chemical means.
Compounds are composed of more than one
type of element and can be broken down into
elements by chemical means.
Check What You Recall
6. Classify the following materials as mixtures or
pure substances.
(a) soup
(d) carbon dioxide
(b) bronze
(e) air
(c) oxygen
(f) gasoline
7. Classify the following pure substances as
elements or compounds.
(a) carbon
(b) water
(c) silicon dioxide
(d) nitrogen
•
Mixtures contain more than one type of
element and/or compound. They can be
solutions, which are uniform throughout,
or mechanical mixtures, which have varying
composition throughout.
Matter
Mixtures
Mechanical
Mixtures
Pure Substances
Solutions
Elements
Compounds
Matter can be classified according to the categories shown here.
8. Saltwater is a solution that contains two pure
substances that happen to be compounds:
water and salt.
(a) Suggest a way you could get the salt from
the water.
(b) Is there a physical method by which
you could break down the salt or water
further? Explain your answer.
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What You Should Recall About...Atomic Theory
•
•
A scientific law describes an action or pattern
observed so often that it is assumed to always
occur. For example, the law of conservation
of energy states that energy cannot be created
or destroyed, but can only change form.
A scientific theory is an idea or principle,
validated by scientists, that explains and
predicts events.
•
The atomic theory includes these ideas:
• All matter is composed of incredibly tiny
particles called atoms.
• Atoms cannot be created, destroyed, or
divided into smaller particles by a physical
or a chemical change.
• Atoms of different elements bond in
definite proportions to form compounds.
(c) Only a few investigations are conducted
before a theory is accepted by scientists.
10. During the Middle Ages, alchemists were
researchers who conducted investigations to
try to turn common metals such as lead into
gold. Why did alchemists fail to change lead
into gold?
Check What You Recall
9. Indicate whether the following statements are
true or false. If the statement is false, rewrite
it to make it true.
(a) In science, laws do not explain anything;
they just describe and summarize what
happens.
(b) A scientific theory rarely involves an
explanation of why something happens.
What You Should Recall About...Atoms and the Periodic Table
•
•
96
An atom is the smallest unit of an element
that has the properties of that element. Atoms
are made of even smaller subatomic particles:
protons, neutrons, and electrons.
The following statements are true for any
neutral atom:
• The number of protons is equal to the
number of electrons.
• The number of protons that an atom
of any element has is called the atomic
number.
• The sum of the number of protons and
the number of neutrons in an atom is
called the mass number.
• Protons and neutrons make up nearly all
the mass of an atom. Both neutrons and
protons have about 1840 times more mass
than electrons.
•
•
•
•
•
•
Chemical symbols, such as “B” for boron or
“Sn” for tin, are used to represent elements.
Chemical formulas are used to represent
compounds. For example, water is represented
by the formula H2O.
Elements are listed in the periodic table by
increasing order of atomic number. The
periodic law states that when elements are
arranged by atomic number, their chemical
and physical properties recur periodically.
A horizontal row in the periodic table is a
period. Periods are numbered from 1 to 7.
A vertical column in the periodic table is a
group. Groups are numbered from 1 to 18.
Elements in the same family (group) share
similar physical and chemical properties.
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Check What You Recall
11. Copy and complete the following table.
Facts About Subatomic Particles
Electrons
Location
Protons
inside the
nucleus
Charge
Relative
size
Neutrons
positive ()
smallest
of these
particles
12. The atomic number for nitrogen is 7. How
many protons and electrons does an atom of
nitrogen have?
13. What is the chemical symbol for these
elements?
(a) gold
(d) argon
(b) aluminum
(e) silver
(c) antimony
14. What are the chemical symbols for the
following elements: helium, aluminum,
tungsten, cadmium, krypton, francium, cobalt,
and barium? (Refer to a periodic table.)
15. Which element is found in Group 3 and
Period 5 of the periodic table?
16. Only two elements are liquids at room
temperature. Which two are they? (Refer to a
periodic table.)
17. Which of the following is not a classification
of elements represented on the periodic table?
(a) solids, liquids, and gases
(b) metals, non-metals, and metalloids
(c) earth, water, and air
(d) natural elements and synthetic elements
18. List three elements found in Period 2 of the
periodic table.
19. List two elements found in Group 2 of the
periodic table.
20. The noble gases are the elements in Group
18 of the periodic table. These non-metals
are all odourless, colourless gases at room
temperature. Look at the periodic table
and then list the noble gases, including the
chemical symbol for each gas.
21. Identify the information listed below for the
element beryllium. Refer to the periodic table
below.
(a) symbol
(b) name of group
(c) number of protons
(d) number of electrons
(e) atomic number
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U
nderwater documentary films offer a peek into the amazing diversity of ocean
life. Divers use specially designed movie cameras and tanks that let them breathe
underwater. But bubbles from regular scuba gear can scare wildlife and ruin a shot.
That’s where rebreathers come in. A rebreather is a specialized recycling apparatus
that adds oxygen to the air a diver breathes out and removes carbon dioxide from
it. The exhaled carbon dioxide interacts in a water solution with a compound called
calcium hydroxide in the rebreather. A solid substance called calcium carbonate is
produced during this interaction. Removing carbon dioxide (followed by adding
oxygen) allows exhaled air to be breathed again and again. No gas bubbles are
released to the surroundings.
The change that occurs when carbon dioxide interacts with calcium hydroxide
is one example of a chemical reaction. In this chapter, you will learn how to use the
names and chemical formulas of different compounds to describe what happens to
them, and to their properties, during chemical reactions.
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LAUNCH ACTIVITY 3
A Carbon Dioxide Generator
In your body, cellular respiration consumes oxygen and
generates carbon dioxide. But other chemical changes
can also generate carbon dioxide.
What to Do
1. Set up the apparatus as shown. Add about 100 mL
limewater to the beaker.
Safety Precautions
2. Place half a scoop of baking soda in the flask. Add
half a scoop of citric acid. Swirl the solids together
and record your observations.
• Dispose of materials as your teacher directs.
3. Add 20 mL of water to the flask and quickly place
the stopper on the flask. Swirl the flask.
Materials
•
•
•
•
•
•
•
•
•
250 mL Erlenmeyer flask with side arm
stopper
tubing
150 mL beaker
scoopula
25 mL graduated cylinder
baking soda
citric acid
limewater
4. Observe what is happening both in the flask and the
beaker. Record your observations.
What Did You Find Out?
1. Did a reaction occur in the flask? In the beaker? How
do you know?
2. In the test for carbon dioxide, the compound calcium
hydroxide in the limewater reacts with carbon
dioxide to form the compound calcium carbonate
and water. How did the appearance of the liquid
in the beaker change over time? What does this
mean in terms of the amount of calcium carbonate
produced?
3. Why do you think water was required for the
reaction to proceed? Would a reaction have occurred
if either citric acid or baking soda were left out?
4. How does this activity relate to what happens in a
rebreather, described on the facing page?
What You Will Learn
Why It Is Important
In this chapter, you will
• describe the differences between ionic and
molecular compounds
• name compounds and write their formulas
• write chemical equations
Chemically literate people can make informed
decisions about what products to buy and use and
to help reduce human impact on the environment.
A key part of chemical literacy is being able to
interpret chemical names and formulas, as well as
understand the chemical equations that represent
those reactions.
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3.1 Ionic and Molecular Compounds
What Do You Think?
• What are some examples of chemical compounds at home, and what are their
properties or uses?
• What kinds of things do people at home and in the workplace need to know
about the properties of substances to use them safely?
• What is the value of using the formula H2O to represent water or the formula
NaCl to represent table salt?
Key Terms
molecular compound
molecule
ion
ionic compound
Many of the chemical compounds in products that people use at home,
school, and work have properties that make them both beneficial and
potentially dangerous. For instance, compounds that include the element
chlorine are included in many household cleaners because of their strong
disinfectant properties. Chlorine kills bacteria and many other organisms
because it is toxic (poisonous) to them. Its toxicity is what makes chlorine
useful. However, its toxicity also means that people must use chlorine
with great care.
Chlorine compounds are also used on a large scale to disinfect
drinking water and swimming pool water, as shown in Figure 3.1.
Although chlorine compounds are widely used, they must be produced,
used, and disposed of carefully because of the hazardous nature of their
properties. Many other compounds contained in cleaning products are
also potentially dangerous, even though they are also useful for cleaning.
That’s why many products sold for use in the home have hazard symbols
and safety warnings on their packaging, as shown in the image on the
next page.
Figure 3.1 To keep the water in swimming pools free of harmful bacteria and other microbes,
compounds containing chlorine are often added to the water to disinfect it.
Infer Since chlorine is toxic to all organisms, including humans, what factors do you think are taken
into account in order to add chlorine to swimming pools so they are safe for people?
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3-1A Can You Judge a Product by Its
Label?
F i nd Out ACTIV ITY
Products used in the home have properties that make them useful for jobs such as cleaning clothes or shining glass. But these
properties can also make them dangerous. Many home products that are potentially dangerous have safety warnings on their
labels. Hazardous Household Product Symbols (HHPS) are designed to be easy to understand. The shapes that outline the
pictures are designed to look like road signs.
The PICTURE tells you the
TYPE of danger
READ THE LABELS EVERY TIME
AND STAY SAFE
There are two frames used around the symbols:
EXPLOSIVE The container can
explode if heated or punctured.
Flying pieces of metal or plastic
from the container can cause
serious injury, especially to eyes.
This frame means
that the container
is dangerous.
This frame means that
the contents inside the
container are dangerous.
CORROSIVE The product can
burn your skin or eyes. If
swallowed, it will damage your
throat and stomach.
FLAMMABLE The product or
its fumes will catch fire easily if it
is near heat, flames or sparks.
Rags used with this product may
begin to burn on their own.
POISON If you swallow, lick, or
in some cases, breathe in the
chemical, you could become very
sick or die.
symbol
signal word
CAUTION means temporary injury
may be frequent. Death may occur
with extreme exposure.
DANGER means may cause
temporary or permanent injury or
death.
EXTREME DANGER means
exposure to very low quantities may
cause death or temporary or
permanent injury.
What to Do
1. Work in small groups. Your teacher will provide your
group with an empty container for a common product
used in the home or a label from a common product.
Examine the label carefully.
2. What is the intended use of the product?
3. What substance or substances are found in the
product?
4. What, if any, hazard-related information is included on
the product labelling?
5. What, if any, safety-related instructions are provided?
6. Your teacher will provide MSDS for some of the
substances in the product. What information is provided
on an MSDS?
What Did You Find Out?
1. As a class, share some of the names of the substances
listed on the label.
The back or side label of regulated containers will always
have some type of bordered area. Inside the border. you
will find safety instructions, the words FIRST AID
TREATMENT along with instructions in case of injury
and a list of harmful substances in the product.
Avoid contact with eyes. Avoid inhalation.
FIRST AID TREATMENT
This product contains ammonia.
If splashed in eyes or on skin, flush thoroughly with water.
If swallowed, drink large amounts of water. DO NOT INDUCE
VOMITING. CALL PHYSICIAN OR POISON CONTROL
CENTRE IMMEDIATELY.
KEEP OUT OF REACH OF CHILDREN
2. Which substances are familiar to you? Which substances
are unfamiliar?
3. Based on the names of the substances, what similarities
and differences do you notice between ingredients in
the products?
4. Do you notice significant differences between products
that are labelled “green” and those that are not?
5. What do you think happens to the substances in these
products once they are used in your home?
6. Should people stop using products that contain
potentially dangerous compounds? Defend your answer.
7. How do the HHPS symbols compare with the WHMIS
symbols? Refer to the front of your textbook to remind
yourself of the WHMIS symbols.
8. Choose one compound from the class list. Conduct
research to find out about its properties and any issues
related to its production, use, or disposal. Briefly report
your findings to the class.
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Chemical Compounds
Did You Know?
How many compounds are
currently known to science? It
is a difficult question to answer
because there are so many.
Estimates differ, but all agree
that there are many millions.
Scientists also agree that many
millions more are possible–
over 100 000 new compounds
are being made each year.
One method for adding chlorine to the water in a pool involves breaking
down sodium chloride, also known as table salt. (A certain company that
uses this method brags that they use only the finest Nova Scotia salt!)
Water and sodium chloride are both examples of chemical compounds.
Some other familiar examples are shown in Figure 3.2.
In chemical terms, compounds are made of elements that are
chemically combined in specific proportions. Take a look at the periodic
table at the back of your book. There are 92 naturally occurring chemical
elements, most of which can combine with one or more other elements to
form compounds. Imagine how many combinations are possible!
Two Categories for Compounds
As you can see in Figure 3.2, even commonplace compounds have a wide
variety of properties. One way that chemists make sense of compounds
and their properties is to classify them. And two categories that chemists
use for compounds are molecular compounds and ionic compounds.
Chemicals in these two categories share similar properties, which can be
explained by their structure at the atomic level.
air – a mixture of elements and molecular compounds that include carbon dioxide and water
wood – mainly cellulose,
a molecular compound
made of carbon, hydrogen,
and oxygen
melamine plastic –
molecular compounds
made of carbon, nitrogen,
and hydrogen
butter – a mixture of molecular
compounds made of carbon,
hydrogen, and oxygen
sugar – a molecular compound
made of carbon,
hydrogen, and oxygen
molecular compound a
compound formed of
atoms of two or more
elements that share
electrons
molecule particle formed
by two or more atoms
joined by covalent bonds
102
table salt – an ionic compound
made of sodium and chlorine
baking soda –
sodium hydrogen carbonate,
an ionic compound
made of sodium, hydrogen,
carbon, and oxygen
eggshells – calcium carbonate,
an ionic compound made of
calcium, carbon, and oxygen
Figure 3.2 Chemical compounds include objects we use, food we eat, and the air we breathe.
Analyze What patterns in the properties of these ionic and molecular compounds do you notice?
Molecular Compounds
Water, sugar, and carbon dioxide may seem like very different substances.
Water is a clear liquid at room temperature, while sugar is a white solid
and carbon dioxide is a clear gas. But they have one important thing in
common that makes them all molecular compounds. All three substances
are made of atoms of non-metal elements joined together as molecules.
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Molecules
A molecule is the smallest independent unit of a molecular compound,
and it consists of atoms of different elements bonded together. For
example, water consists of two hydrogen atoms and one oxygen atom
bonded together as shown in Figure 3.3. The bonds between the atoms
are called covalent bonds and they are very strong. Covalent bonds form
when atoms share electrons. Think of a covalent bond as a tug-of-war
game. Two teams are joined by the rope but prevented from coming
together by the opposite forces they are exerting.
oxygen
atom
covalent
bonds
hydrogen atoms
Figure 3.3 Water is composed of
molecules. Water molecules consist of
two hydrogen atoms bonded to one
oxygen atom.
Explaining Some Properties of Molecular Compounds
Molecular compounds have widely varying properties. The plastic casing
of a ball-point pen, the components of gasoline, the strongly scented
compounds in a banana, and the carbon dioxide that we exhale with
every breath are all molecular compounds. But there are some properties
that many molecular compounds share, due to the way molecular
compounds are structured at the molecular level.
Although the bonds that hold atoms together in molecules are very
strong, the bonds that attract one molecule to another in a molecular
compound are relatively weak, as modelled in Figure 3.4. When you
melt or vaporize a molecular compound, you need to supply enough
energy to overcome the attraction between the molecules. Because this
attraction is weak, most molecular compounds boil and melt at relatively
low temperatures. This property also explains the relative softness of
molecular compounds.
In addition, because molecular compounds do not have free electrons
or ions, they are relatively poor conductors of electricity and heat. Figure
3.5 shows an application of this property.
strong covalent bonds
relatively weak bonds
Figure 3.4 The bonds that hold atoms together in molecules—covalent bonds—are very strong.
Compared to these covalent bonds, the bonds that hold one molecule to another are very weak.
Figure 3.5 Molecular compounds are
poor conductors of electric current.
This makes them useful as insulating
covers for computer cables.
Apply Why is it important that covers
for electrical wires not conduct electric
current?
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Ionic Compounds
ion an atom or group of
atoms with a positive or
negative charge
ionic compound a
compound composed of
oppositely charged ions
held together with ionic
bonds
Some compounds are not made of molecules. Instead, they are made of
ions. An ion is an atom or group of atoms with a positive or negative
charge. Compounds made of ions are called ionic compounds. Ionic
compounds consist of negatively charged ions and positively charged
ions held together with ionic bonds, which is the name for the attraction
between oppositely charged ions. Ionic bonds are very strong.
Ionic compounds containing two elements form when atoms of one
element each lose one or more electrons to atoms of the second element.
For example, table salt, sodium chloride, forms when sodium atoms each
transfer one electron to chlorine atoms. Each sodium atom becomes
positively charged: a positive ion. Each chlorine atom becomes negatively
charged: a negative ion. This is what happens when sodium metal reacts
with chlorine gas to form sodium chloride, as shown in Figure 3.6.
→

sodium
chlorine
sodium chloride
e–
Na
Cl
Na+
Cl–
Figure 3.6 A sodium atom loses one electron to a chlorine atom, forming a sodium ion, Na, and a
chloride ion, Cl. Joined by strong ionic bonds, they form the compound sodium chloride.
Word Connect
The term “ion” comes from
a Greek word that means
“going.” Physicist Michael
Faraday (1791–1867) first
used the term for substances
that conduct electric current
in solution—in other words,
substances that allow the
current to “go.”
104
Check Your Understanding
1. What is a molecule? Provide a sketch as part of your answer.
2. Give two examples of molecular compounds.
3. “The bonds in molecular compounds are very strong.” Do you
agree or disagree with this statement? Explain your answer.
4. Why do molecular compounds tend to boil and melt at relatively
low temperatures?
5. What is an ion? Give two examples of ions.
6. Give two examples of ionic compounds.
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Think About It
3-1B Patterns in Ion Formation
2. Look at the groups of the periodic table. What patterns
in ion charges do you notice?
What Did You Find Out?
1. Refer to the periodic table. What ions are formed by
elements from Groups 1, 2, 16, 17, and 18? Make
generalizations for each.
2. What are some elements you would not expect to find
in ionic compounds? Explain your answer.
What to Do
1. Take a look at the periodic table. Notice that many of
the element cells have one or more charges listed in
the upper righthand corner. According to the periodic
table’s key, what are these charges?
The Structure of Ionic Compounds
Unlike molecular compounds, ionic compounds do not consist of discrete
units (molecules). Instead, they form large structures with regular and
repeating patterns called lattices. The cubic structure of sodium chloride
is an example of a lattice. Notice the cubic shape of the sodium chloride
crystals in the magnified image in Figure 3.7. A model of the lattice
arrangement of ions of sodium chloride is shown in Figure 3.8.
Figure 3.7 This scanning electron microscope image shows smaller sodium chloride crystals on a
large crystal. The image has a magnification of 558x. Each crystal contains millions and millions of
sodium ions and chloride ions.
Figure 3.8 A crystal of sodium
chloride is structured so that six
chloride ions surround every sodium
ion, and six sodium ions surround
every chloride ion. They are all joined
by strong ionic bonds.
Explain Sodium chloride is formed of
charged particles, but the compound
overall has no charge. Why?
Explaining Some Properties of Ionic Compounds
To melt or boil an ionic compound requires breaking the strong ionic
bonds holding the ions together in a lattice structure. Because the bonds
are so strong, a great deal of energy is required to do this. As a result,
ionic compounds tend to melt and boil at very, very high temperatures.
For example, the melting point of sodium chloride is 801°C.
Ionic compounds do not conduct electricity in the solid state. Even
though they are made of ions, those ions are held rigidly in place.
Charged particles that can move are required to conduct an electric
current. Ionic compounds dissolved in water or melted ionic compounds
do, however, conduct electricity. In those forms, the ions in ionic
compounds are free to move around.
Suggested Activity
Investigation 3-1C: Properties of
Ionic and Molecular Compounds
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3-1C
Properties of Ionic and Molecular Compounds
SkillCheck
• Recording
Although each compound has unique properties, there are some similarities in these
properties that can help you to tell what kind of compound it is. In this investigation,
test six different compounds to determine whether they are ionic or molecular.
• Analyzing and Interpreting
Question
• Communicating
How can you use properties to classify compounds as ionic or molecular?
• Observing
Procedure
1. Label six test tubes A to F. Place samples of six different compounds in the test
tubes. Use enough of each compound to fill the rounded bottom of the test tube.
Safety Precautions
2. Prepare a table like the one shown. It should take up one full page so you have
enough space for all your observations. Give your table a title.
Substance
•
•
Wear safety eyewear and a
lab apron.
Crush
Test for odour cautiously.
Do not smell any chemicals
in the laboratory directly.
Follow the instructions given.
Melting
•
Treat the hot plate carefully.
Do not leave it turned on
for more than 2 min. Allow
it to cool for 15 min before
moving it.
•
To unplug the hot plate, do
not pull on the cord. Pull on
the plug.
Materials
•
6 test tubes with stoppers
•
6 samples of compounds
•
glass plate or watch glass
•
scoop
•
plastic water bottle
•
hot plate
•
aluminum foil
•
distilled water
•
conductivity tester
•
tongs
106
A
B
C
D
E
F
Hardness
Solubility
Conductivity
TOTAL score
3. Perform the following tests on each compound. At each test step, analyze all
the compounds before moving on to the next test. If a substance responds like
a molecular compound, record a score of one (1). If a substance responds like
an ionic compound, record a score of zero (0). Also record short, descriptive
observations for each test in your table.
Crush Test
Place one or two grains of the compound on a glass plate or watch glass. Press
on the compound with a scoop or another metal tool. Ionic compounds withstand
considerable force and then crush suddenly into a gritty powder (score 0). Solid
molecular compounds are often more flexible and crush like wax or plastic (score 1).
Hardness Test
You must wear gloves for this test. Wash and dry your gloves after each substance.
Rub some of each compound on a clear plastic water bottle. Ionic compounds are often
hard enough to scratch the plastic (score 0). Molecular compounds are seldom hard
enough to scratch the plastic (score 1).
Melting Test
Spread a square of aluminum foil to cover the entire surface of the hot plate. Carefully
place one small piece (no larger than half a grain of rice) of each substance on the
aluminum. Place the samples as far apart as possible but avoid the edges of the hot
plate. Plug the hot plate into the electric outlet. Turn on the hot plate. Ionic compounds
do not melt except at very high temperatures (score 0). Many molecular compounds
melt at relatively low temperatures (score 1). Turn off the hot plate after 2 min. When
the hot plate has cooled, pull out the plug. Do not pull on the cord.
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Conduct an InVesTIgATIOn
Solubility Test
Each test tube should still contain most of the original substance. Add 10 mL of
distilled water to each of the test tubes. Stopper each test tube. Keeping your fingers
on the stopper and test tube, gently shake or swirl the water and substance together.
Many ionic compounds will dissolve in water, although there are exceptions
(score 0). Many molecular solids are insoluble in water (score 1), although again there
are exceptions.
Conductivity Test
Use a conductivity tester to test the conductivity of the solution in each test tube.
When ionic compounds dissolve, the resulting solution will conduct electricity
(score 0). When molecular compounds dissolve, the resulting solution will usually
not conduct electric current (score 1). Make sure that you clean the probes of the
conductivity tester between readings.
4. Clean up your work area. Dispose of all the compounds as indicated by your
teacher. Return each piece of equipment to its place.
Analyze
1. Add up the scores for each compound. A low score, near 0, indicates that a
compound is ionic. A high score, near 6, indicates that the compound is molecular.
What patterns do you see?
2. If a compound has a score of 2, 3, or 4, use your descriptive observations to help
you decide whether it is ionic or molecular.
Conclude and Apply
1. Summarize your classification of each substance including a rationale for each
decision.
2. What was the purpose of assigning a number to each test? Did the numbers have
any scientific meaning?
3. If you could perform only two tests to identify ionic and molecular compounds,
which two tests would you choose? Explain your thinking. If these tests are more
important than the others for classifying, how could you reflect that in the scoring
system if you were to perform the investigation again?
4. Your teacher will tell you the names and formulas of the compounds. What do the
names and formulas tell you, if anything, about the compounds?
5. Examine the element symbols in the chemical formulas. What do you notice about
the elements that are in the formulas for the ionic compounds compared to the
elements that are in the formulas for the molecular compounds?
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Testing, Testing…with Tox21
In 2010, the explosion and fire on the drilling rig
Deepwater Horizon sent oil gushing into the Gulf of
Mexico, endangering wildlife and the environment.
Officials had to act quickly. Part of the response was
to use a certain group of chemicals to disperse the oil,
allowing for easier clean-up. First, however, government
scientists needed to test the chemicals to ensure they did
not pose a threat to human health. And they needed to
do it fast.
For this work, it helped to have a bright yellow robot
as a lab assistant. A high-speed robotic arm conducted
the tests for potential toxicity without having to expose
humans or other living things to the chemicals. Using the
robot was speedy and efficient. In just one day, the robot
could run tests that would keep a human lab technologist
busy for a year.
The Tox21 testing system is a significant new tool
for the science of toxicology, which is the study of how
chemicals can act as poisons when they react with other
chemicals in living things and in the environment. The
system represents a revolutionary shift in the science,
which is moving from testing a few doses on animals, to
the ability to test chemicals at a broad range of dosages
using cells in the laboratory.
Eventually, the Tox21 system will be able to assess
over 10 000 chemicals. Working day and night, 7 days
a week, it will also help reduce the backlog of untested
chemicals—a task that will save time and money, while
vastly improving our understanding of chemical toxicity.
The Tox21 Robot
The robot is part of a screening system called Tox21.
The system is an assessment tool that helps protect the
health of humans and the environment by testing how
chemicals react with laboratory preparations of living
cells. Scientists want to understand how the chemicals
found in various products, including food additives and
prescription drugs, react with the chemicals already
present in the human body and the environment.
In the past, toxicity tests were often done on animals.
In the Tox21 system, however, a test chemical is added to
a plate that has about 1500 small depressions or wells.
Each well holds a different type of cell derived from
human tissues. As the robot scans the cells to record any
chemical reactions between the test chemical and the
cells, scientists monitor the resulting data on computer
screens. Any chemicals that disrupt normal cell function
are cause for concern.
108
Questions
1.
Describe the advantages of using the Tox21
system over the ways that toxicology studies
have been done in the past.
2.
Why is it important that different dosages of
chemicals be tested on animal cells?
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Checking Concepts
1. Using an example, explain how a compound
can have properties that make it both useful
and hazardous.
2. What does the acronym HHPS stand for, and
what shapes are used to indicate the level of
danger? Include the symbols that are used in
the classification on HHPS labels.
3. Identify two categories that chemists use to
classify compounds. Explain how a compound
is classified into one of these two categories.
4. Describe the difference between an atom and
an ion.
5. Identify which of the following are chemical
compounds: an iron nail, ice cream, hand
sanitizer, a plastic bottle, mercury in a
thermometer, air, paper.
6. Make a table to compare ionic compounds
and molecular compounds. Include columns
for examples of each and descriptions of
characteristic properties.
7. Compare and contrast the bonds in molecular
compounds and ionic compounds.
8. Ionic compounds are made up of charged
particles, ions, and yet the compounds
themselves are electrically neutral. How is this
possible?
9. An element on the periodic table has a 3
in the upper right hand corner of its element
cell. What does this 3 mean?
Understanding Key Ideas
10. Explain the term “lattice structure” as it
applies to an ionic compound such as sodium
chloride.
11. Explain why calcium chloride does not
conduct electric current as a solid but does
conduct electric current in solution.
12. In a small coastal fishing village, the
community works together to catch, clean,
process, and ship their products to the
rest of the world. If the population of the
community were atoms, would the village be
more like a molecular or an ionic compound?
Explain your answer.
13. If a new element has been discovered that is
found to behave chemically like sodium, is it
more likely to form ionic or covalent bonds in
compounds? Explain your answer.
14. Consider the following observations.
• In most places, tap water conducts electric
current.
• Purified water that contains no dissolved
substances conducts very little electric
current, but it does conduct some.
• In the liquid state, a small percentage of
water molecules form the ions H and OH.
Based on these observations, answer the
following questions. Explain each answer.
(a) Would you expect a sample of water
consisting only of water molecules to
conduct electric current?
(b) What type of compound is likely
contained in tap water?
(c) Why is it important to make sure your
hands are dry when working with
electrical equipment?
(d) Why does even water from which all other
compounds have been removed conduct
electric current to a small extent?
15. Candle wax is soft to the touch and requires
only a small amount of heat to melt. Would
these two observations lead to the conclusion
that the candle wax is an ionic or a molecular
compound? Explain your answer.
16. An element in Group 1 on the periodic table
forms ionic compounds with elements in
Group 17 in a 1:1 ratio. What ratio would
you expect an element from Group 2 and
elements from Group 16 to have when they
form ionic compounds? Explain your answer.
17. Would you expect melted magnesium
chloride to conduct electricity? Explain your
answer.
Project Prep
Why is it important to understand the
properties of different categories of compounds
when planning and analyzing a chemical
investigation?
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3.2 Names and Formulas of Ionic
and Molecular Compounds
Key Terms
binary ionic compound
What Do You Think?
• Imagine that you have to create unique, distinctive names for a set of one
hundred or more objects such as seashells or computer emoticons. What criteria
(characterizing features) could you use?
• One example of a criterion for naming a compound is that the name should
indicate something about its composition. What other criteria do you think
scientists use to name ionic compounds and molecular compounds?
• What information does a chemical formula such as NaCl convey?
Think About It
3-2A What’s in a Name?
Are there any patterns in the names of molecular and
ionic compounds? Work with a partner to discover what
information you can get from some chemical names. Note
that each compound in this activity is composed of two
elements only.
2. Review the names of the ionic compounds listed below.
Notice where each element in the compound is located
on the periodic table. List at least two patterns that
you can find in how these names are written. Write at
least two questions that you have about the names of
ionic compounds.
(a) sodium bromide
(b) magnesium sulfide
(c) iron(III) oxide
(d) lead(IV) nitride
(e) aluminum fluoride
(f) calcium chloride
What Did You Find Out?
What to Do
1. Review the names of the molecular compounds listed
below. Note where each element in the compound is
located on the periodic table. List at least two patterns
that you can find in how the names are written. Write
at least two questions that you have about the names
of molecular compounds.
1. What are two ways to distinguish ionic compounds
from molecular compounds based on the compounds'
names?
2. What information is included in the name of a
molecular compound that is not included in the name
of an ionic compound?
(a) dinitrogen trioxide
(b) nitrogen trichloride
(c) carbon disulfide
(d) tetraphosphorus decaoxide
(e) phosphorus pentabromide
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Names of Binary Ionic Compounds
The large bulging mass around the person’s neck in Figure 3.9 is called
a goitre. Such a growth is caused by iodine deficiency. This problem
is uncommon in developed countries because the ionic compound
potassium iodide is added to our table salt.
Potassium iodide is an example of a binary ionic compound. In
chemistry, “binary” means “composed of two elements.” Binary ionic
compounds are composed of ions of one metal element and ions of one
non-metal element joined by ionic bonds. The name of a binary ionic
compound comes from the names of its elements as described below.
• The first part of “potassium iodide” names the positive ion,
potassium, K. The positive ion is always a metal in a binary ionic
compound. The positively charged metal ion is always named first. Its
name is the same as the name of its element.
• The second part of “potassium
iodide” names the negative ion,
iodide, I, an ion of iodine.
The negative ion in a binary
ionic compound is always a
non-metal. The name of the
negative ion in a binary ionic
compound always ends with the
suffix “-ide.” (The negative ion
of iodine is iodide.)
The names and symbols of common
negative ions of non-metals are
shown in Table 3.1. The ion
charges are also found on the
periodic table at the back of your
textbook.
binary ionic compound
a compound composed
of ions of two different
elements: a positively
charged metal ion and a
negatively charged nonmetal ion
Figure 3.9 The goitre shown here
results from a thyroid gland that
enlarges as it attempts to absorb more
iodine. Fish are an excellent natural
source of iodine, so people who live
near the sea and eat a lot of fish are
not likely to suffer from goitres caused
by iodine deficiency.
Table 3.1 Ions of Non-metals
Element
Ion
Symbol
Group
fluorine
fluoride
F
17
chlorine
chloride
Cl
17
bromine
bromide
Br
17
iodine
iodide
I
17
oxygen
oxide
O2
16
sulfur
sulfide
S2
16
selenium
selenide
Se2
16
nitrogen
nitride
N3
15
phosphorus
phosphide
P3
15
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positive ion (Al3+)
negative ion (O2–)
Al2O3
subscripts
Figure 3.10 Anatomy of the formula
of an ionic compound. Formulas for
ionic compounds are always written
with the positive ion first and the
negative ion second. In binary ionic
compounds, the positive ion is a
metal and the negative ion is a
non-metal.
Interpreting the Chemical Formula of an Ionic Compound
The chemical formula of a binary ionic compound contains element
symbols to identify each ion. The positively charged metal ion comes first
and the negatively charged non-metal ion comes second, as shown in
Figure 3.10.
Some formulas have small numbers, called subscripts, written to the
right of one or both symbols. The subscripts indicate the ratio of each
type of ion in the compound. If no subscript is shown, you assume the
number to be 1. For example, the formula Ag2O means Ag2O1. Examine
Figure 3.11 to see some examples of chemical formulas of binary ionic
compounds, and their meanings.
MgCl2
KI
K+
I–
Al2O3
Cl–
O2–
1 K ion : 1 I ion
+
–
Mg2+
Cl–
Al3+
O2–
Al3+
O2–
1 Mg2+ ion : 2 Cl– ions
2 Al3+ ions : 3 O2– ions
Figure 3.11 The subscripts in chemical formulas of ionic compounds tell you the ratio of the ions in
the compound.
3-2B The Structure and Formulas of
Ionic Compounds
As you know, ionic compounds consist of ions bonded
together. For example, sodium chloride (table salt) is made
of sodium ions and chloride ions. The diagram below
represents part of a salt crystal. From the diagram, you
can see how a crystal of salt is structured. How does the
structure relate to the formula of sodium chloride?
Cl
Na
Think About It
What to Do
1. Examine the diagram carefully to see how the sodium
and chloride ions are arranged.
2. Count the total number of ions of each element that are
represented in the model.
(a) How many sodium ions are represented?
(b) How many chloride ions are represented?
What Did You Find Out?
1. What is the ratio of sodium ions to chloride ions in
sodium chloride? In other words, how many sodium
ions are there for every one chloride ion?
2. The chemical formula for sodium chloride is NaCl. Based
on this model, should the formula be Na18Cl18? Explain
why or why not.
3. What does the formula NaCl mean?
4. Given the chemical formula of the ionic compound
beryllium fluoride, BeF2, what do you expect to be the
ratio of beryllium ions to fluoride ions?
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Check Your Understanding
7. Examine the periodic table and compare it with Table 3.1. What
do you notice about the locations of the elements listed in the table
and the charges of the ions they form?
8. Which of the following ionic compounds are binary ionic
compounds and which are not? Explain your answer.
(c) NaNO3
(d) NH4Cl
(a) KCl
(b) Al2O3
9. Write the names of ionic compounds containing the following
elements.
(a) rubidium and bromine
(b) oxygen and magnesium
(c) strontium and fluorine
10. Write the names of the following ionic compounds.
(c) MgSe
(e) Li3N
(g) BeF2
(a) KBr
(b) MgCl2
(d) Na2S
(f) AlBr3
(h) RbBr
Writing Formulas of Ionic Compounds
Although an ionic compound is made up of ions, overall the compound
is electrically neutral—it has no charge. So the positive charges on the
metal ions must balance the negative charges on the non-metal ions. For
example, in aluminum oxide, Al2O3, there are two aluminum ions, Al3,
and three oxide ions, O2. What is the total charge?
Charge from Al3
Charge from O2
There are 2 aluminum ions in the formula,
each with a charge of 3.
2  (3)  6
There are 3 oxide ions in the formula, each
with a charge of 2.
3  (2)  6
Total charge: (6)  (6)  0
When writing the formula of a binary ionic compound, you first need
to determine the charges on the ions. Table 3.1 lists the ions of nonmetals. For metals that form only one type of ion, all you need to do
to figure out the ion charge is to look at the periodic table, as shown in
Figure 3.12. (You can find the charges for non-metal ions on the periodic
table, too.) Once you know the charges, you can figure out the formula.
Group 1 metals all form ions
with a charge of 1+.
Group 2 metals all form ions with
a charge of 2+.
Notice that some metals
can form more than one ion.
Figure 3.12 The periodic table lists
the charges of ions commonly formed
by the various elements.
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Sample Problem: Writing the Formulas of Ionic
Compounds
Problem
What are the chemical formulas of
(a) calcium chloride?
(b) aluminum sulfide?
Solution
(a) calcium chloride
1. Identify each ion and its charge.
chloride: Cl
calcium: Ca2
2. Determine the number of ions needed to balance positive
charges with negative charges. In this case, two chloride ions
are needed to balance the charge on calcium.
Charge from Ca2
Charge from Cl
A calcium ion has a charge of 2.
A chloride ion has a charge of 1.
Therefore, two chloride ions are
needed to balance the charge of
one calcium ion.
2  (1)  2
1  (2)  2
3. Use subscripts to write the formula. Remember to write the
metal ion first. Do not include a subscript if the subscript
would be “1.”
The formula for calcium chloride is CaCl2.
Solution
(b) aluminum sulfide
1. Identify each ion and its charge.
sulfide: S2
aluminum: Al3
2. Determine the number of ions needed to balance positive
charges with negative charges. In this case, two aluminum ions
are needed to balance the charges on three sulfide ions.
Charge from Al3
Charge from S2
An aluminum ion has a charge of
3.
The lowest common multiple of 3
and 2 is 6. To get 6, multiply 3
by 2.
2  (3)  6
A sulfide ion has a charge of 2.
To get 6, multiply 2 by 3.
3  (2)  6
3. Use subscripts to write the formula. Remember to write the
metal ion first. Do not include a subscript if the subscript
would be “1.”
The formula of aluminum sulfide is Al2S3.
continued on next page
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Sample Problem: Writing the Formulas of Ionic
Compounds—continued
Check Your Solution
In each case, the symbol for the metal is written first and the
symbol for the non-metal comes second. The ratio of charges
results in a neutral compound in both cases.
For CaCl2: 1  (2)  2  (1)  0
For Al2S3: 2  (3)  3  (2)  0
Practice Problems
1. Write the formulas of the ionic compounds containing the
following ions.
(a) Na and Br
(b) K and S2
(c) Zn2 and I
(d) Mg2 and N3
2. Write the formulas of the following ionic compounds.
(a) sodium iodide
(f) aluminum iodide
(b) zinc oxide
(g) aluminum phosphide
(c) magnesium chloride
(h) calcium oxide
(d) potassium selenide
(i) calcium sulfide
(e) silver sulfide
(j) rubidium bromide
3. Silver iodide has a crystal structure similar to ice and can cause
water to freeze. It has been used in rainmaking experiments,
in which a substance is released into clouds to try to induce
precipitation. A silver iodide generator is shown in
Figure 3.13. What is the chemical formula of silver iodide?
Figure 3.13 This Cessna 210 single-engine airplane is equipped with a silver iodide generator. It is
designed for cloud seeding experiments.
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Word Connect
As their name suggests,
Roman numerals were first
used by the ancient Romans.
Their numeral system used
letters from the Latin
alphabet —I (1), V (5), X (10),
L (50), C (100), D (500), and
M (1000)—to express large
and small numbers. For
example, the year 2012 is
MMXII in Roman numerals.
Multivalent Metals
As you can see when you examine the periodic table, some metals form
more than one type of ion. Such metals are called multivalent metals.
For example, copper can form ions with a 1 or 2 charge, as shown
in Figure 3.14. To distinguish between the ions, a Roman numeral
is written after the name of the metal. For example, Cu is written as
copper(I), pronounced “copper one.” Cu2 is written as copper(II),
pronounced “copper two.” On the periodic table, the ion charges for a
given element are listed with the most common charge at the top and the
least common charge at the bottom.
Figure 3.14 Although both of these
compounds contain copper and oxygen,
copper(II) oxide, CuO, is black and
copper(I) oxide, Cu2O, is red.
Infer What does the colour difference
indicate about the two samples?
Chemical Formulas and Names of Ionic Compounds
Containing Multivalent Metals
Figure 3.15 Like many compounds
of chromium, chromium(III) chloride
is vividly coloured. In fact, the name
“chromium” comes from the Greek
word for “colour.”
116
To write the chemical formula of a multivalent metal, follow the same
process as for the binary ionic compounds you have been naming so far.
The only difference is that you cannot tell the charge on the metal ion by
looking at the periodic table because there will be more than one choice.
Instead, look at the Roman numeral in the name, which will tell you the
charge.
Table 3.2
The Roman numerals for charges 1
Roman Numerals
through 7 are given in Table 3.2.
Metal Ion
Roman
For example, the name chromium(III)
Charge
Numeral
chloride (shown in Figure 3.15) tells you
1
I
that the chromium ion in the compound is
3

Cr . The chloride ion is Cl . For a neutral
2
II
compound, there must be three chlorine
3
III
ions for every one chromium ion,
4
IV
so the formula is CrCl3.
5
V
When naming a compound that contains
6
VI
a multivalent ion, you must include a
7
VII
Roman numeral to show which charge the
ion has. You can determine the charge of the
positive ion by determining the charge of the negative ion in the
compound, as shown in the Sample Problem on the next page.
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Check Your Understanding
11. What is the name of each of the following metal ions?
(b) Ni3
(c) Au
(d) Ti4
(a) V4
12. Write the formula for these compounds with a multivalent metal.
(a) nickel(III) chloride
(c) copper(I) oxide
(b) lead(IV) sulfide
(d) copper (II) oxide
Sample Problem: Naming an Ionic Compound with a
Multivalent Metal
Problem
The compound Fe2O3 is used as a source of iron in the steel
industry. Figure 3.16 shows an example of Fe2O3 in nature. What
is the name of Fe2O3?
Solution
1. Identify the ions.
The ion of iron may be either Fe2 or Fe3.
The ion of oxygen is O2.
2. Determine the ratio of ions in the compound.
• According to the formula, the compound has 2 iron ions
for every 3 oxygen ions.
3. The negative charges and the positive charges must be equal
in magnitude. Determine which of the two possible iron ions
achieves this balance.
• Since there are 3 oxygen ions, there is an overall negative
charge of 6.
• Since there are 2 iron ions, they must have a charge of 3
to give an overall positive charge of 6.
4. Write the name of the compound using a Roman numeral to
indicate the charge of the metal ion.
• The name of Fe2O3 is iron(III) oxide.
Check Your Solution
Figure 3.16 The famously red soil of
Prince Edward Island gets its colour
from compounds of iron, including
Fe2O3(s).
Two Fe3 ions have a charge of 6. Three O2 ions have a charge
of 6. The charges balance.
Practice Problems
4. Write the names of the compounds with the following ions.
(c) Cu2 and Cl
(a) Co3 and O2
(b) Mn4 and S2
(d) Cu and Cl
5. Write the names of the following compounds. Each contains
an ion of a multivalent metal.
(e) Ni2S3
(g) PbF4
(a) FeO
(c) SnS2
(b) Cu3N
(d) Sn3N2
(f) NiS
(h) TiS2
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Ionic Compounds Containing Polyatomic Ions
Limestone is an important industrial mineral that is mined in several
locations around Nova Scotia. Limestone is made of an ionic compound
called calcium carbonate, CaCO3, which is also the compound that shells
such as those shown in Figure 3.17 are made of.
The carbonate ion, CO32, is composed of carbon and oxygen atoms.
An ion that, like carbonate, is composed of atoms of more than one
element is a polyatomic ion. Compounds containing polyatomic ions are
not binary compounds because they always contain at least three elements.
But like binary compounds, compounds containing polyatomic ions are
named by writing the name of the positive ion followed by the name of
the negative ion.
Figure 3.17 Shellfish use calcium
carbonate to make their shells.
Research From what sources do
shellfish get calcium carbonate?
Common Polyatomic Ions
There are a limited number of polyatomic ions that regularly occur in
compounds. You can look up their names, formulas, and charges in a table
such as Table 3.3. Notice that the only positively charged polyatomic ion
listed is the ammonium ion, NH4.
Table 3.3 Names, Formulas, and Charges of
Some Common Polyatomic Ions
1 Charge
1 Charge
2 Charge
3 Charge
ammonium,
NH4
acetate, C2H3O2
chlorate, ClO3
chlorite, ClO2
hydrogen carbonate, HCO3
hydroxide, OH
nitrate, NO3
nitrite, NO2
permanganate, MnO4
carbonate, CO32
chromate, CrO42
dichromate, Cr2O72
peroxide, O22
sulfate, SO42
sulfite, SO32
phosphate, PO43
phosphite, PO33
Sample Problem: Writing Chemical Formulas of a
Compound with a Polyatomic Ion
Problem
Calcium nitrate is a key component of nitrogen-containing
fertilizers. Important as a way to increase the yield of farms, such
fertilizers can also cause problems when an excess of nitrogen
enters waterways. What is the formula of calcium nitrate?
Solution
1. Identify each ion and its charge. (Use Table 3.3 or another
table of polyatomic ions to identify the polyatomic ion.)
nitrate: NO3
calcium: Ca2 continued on next page
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Sample Problem: Writing Chemical Formulas of a
Compound with a Polyatomic Ion—continued
2. Determine the number of ions needed to balance positive
charges with negative charges. In this case, two nitrate ions are
needed to balance the charge on calcium.
Charge from Ca2
Charge from NO3
A calcium ion has a charge of 2.
A nitrate ion has a charge of 1.
Therefore, 2 nitrate ions are needed
to balance the charge of one
calcium ion.
1  (2)  2
2  (1)  2
3. Use subscripts to write the formula. If the polyatomic ion
is going to take a subscript, use brackets to enclose the
polyatomic ion before adding the subscript as shown. This
shows that the nitrate ion is a unit, and that there are 2 of
them for each calcium ion.
The formula of calcium nitrate is Ca(NO3)2.
Check Your Solution
The symbol for the metal is written first and the symbol for the
polyatomic ion comes second. The ratio of charges results in a
neutral compound.
1  (2)  2  (1)  0
Practice Problems
6. Write the formula of each of the following compounds.
(a) barium nitrate
(e) sodium dichromate
(b) potassium carbonate
(f) iron(II) chromate
(c) nickel(II) sulfate
(g) lead(IV) acetate
(d) magnesium phosphate
(h) ammonium sulfate
7. There is an error in each of the formulas of the following ionic
compounds. Explain the error and correct each formula.
(a) sodium phosphate, Na3P
(b) magnesium nitrate, MgNO32
(c) potassium sulfite, KSO3
(d) sodium hydroxide, Na(OH)
8. The crystals shown in Figure 3.18 are the largest so far
discovered on Earth. Formed naturally in very hot and humid
conditions, the crystals are made of the compound calcium
sulfate. What is the formula of calcium sulfate?
Figure 3.18 These enormous natural
calcium sulfate crystals are located in
a 290-m-deep cave in Mexico called
Cueva de los Cristales. The conditions
are extreme—50°C and 100 percent
humidity. Even with special breathing
apparatus and cooling suits explorers
cannot endure much more than
30 minutes in the cave.
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3-2C The Ionic Card Game
F i nd Out ACTIV ITY
How well do you understand the rules for naming and
writing formulas for ionic compounds? Apply your
knowledge and creativity to design a chemical card game.
2. Prepare cards and a detailed set of rules for your game.
Materials
4. Exchange games with at least one other group. After
playing each game, complete an evaluation of the
game as directed by your teacher.
• pencils
• felt markers
• index cards
What to Do
1. Work with your group to design a card game that
involves naming and finding formulas for ionic
compounds. Consider the following criteria as you
design your game.
• Your game must include a variety of ions, including
polyatomic ions, and must involve combining them
to make a net charge of zero.
• The game must include at least 15 cards.
• You may base the game on other card games, or you
may invent a new game entirely.
3. Try several rounds of your game within your group.
Refine the rules as necessary.
5. As a class, devise a game you can play with all of the
cards.
What Did You Find Out?
1. What challenges did your group face in designing and
producing the game?
2. How did your game differ from those of other groups?
3. What would you improve about your game if you were
to redesign it? Give reasons for each change.
4. How has producing and playing a card game helped
you to learn and practise naming rules and formulawriting rules for ionic compounds?
• The game should involve two to four players and
require no more than 15 min to complete.
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3-2D Chemical Formulas of Molecular
Compounds
Think About It
Like ionic compounds, molecular compounds are represented by chemical formulas. How do
chemical formulas of molecular compounds compare to chemical formulas of ionic compounds?
Selected Molecular Compounds
Name of
substance
Chemical
formula
Elements
present
How many
atoms of each?
water
H2O
hydrogen,
oxygen
2 atoms H
1 atom O
hydrogen
peroxide
H2O2
carbon
dioxide
CO2
carbon
monoxide
CO
propane
C3H8
glucose
C6H12O6
What to Do
1. Copy the table above. Be sure to leave plenty of room
in the far right column for drawing the molecular
models.
2. Complete the columns with the headings “Elements
present” and “How many atoms of each?”
3. Your teacher has provided molecular models for each of
the compounds. Decide which model represents which
compound and sketch the models to complete the table.
Label each atom with the symbol of its element.
Sketch of molecular model
What Did You Find Out?
1. What do the chemical formulas of molecular
compounds represent?
2. Why is the chemical formula of hydrogen peroxide not
simplified to HO?
3. How do formulas of molecular compounds differ from
those of ionic compounds?
4. Water and hydrogen peroxide both contain hydrogen
and oxygen. Yet they have different properties. Why do
you think this is the case?
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Names and Formulas of Binary Molecular Compounds
binary molecular
compound A compound
composed of atoms of two
different elements, usually
two non-metals, that
are joined together with
covalent bonds
Chemical formulas of binary molecular compounds indicate how many
atoms of each element are present in a single molecule of the compound,
as shown for sulfur hexafluoride, SF6, in Figure 3.19. Like names for
ionic compounds, names for binary molecular compounds have two
parts—one for each element in the compound. The following three rules
will help you write names and formulas of binary molecular compounds.
Figure 3.19 Because of its insulating
properties, and because it does not
react easily with other substances,
sulfur hexafluoride is sometimes used
to insulate double-glazed windows.
The formula for sulfur hexafluoride,
SF6, indicates that there is 1 sulfur
atom and 6 fluorine atoms in each
molecule of the compound.
Rules for Writing Names and Formulas of Binary Molecular
Compounds
Did You Know?
The difference between a
molecule of carbon monoxide,
CO, and carbon dioxide, CO2,
is only one oxygen atom, but
the difference in the properties
of the compounds is a matter
of life and death. Both are
colourless, odourless gases, but
you breathe in carbon dioxide
all day with no ill effects. Air
is 0.03% carbon dioxide and
carbon dioxide is only lethal at
10%. Carbon monoxide, though,
is lethal to humans in very small
amounts—just 0.08%.
122
1. The first element in the name and formula of a binary molecular
compound is usually the one that is farther to the left on the periodic
table.
Example: In carbon monoxide, CO, carbon comes first because carbon is
to the left of oxygen on the periodic table.
2. When naming, the suffix “–ide” is attached to the name of the
second element.
Example: “Oxygen” is changed to “oxide” in the name “carbon
monoxide.”
3. When naming, prefixes are used to indicate how many atoms of each
type are present in one molecule of the compound. Table 3.4 lists
the first 10 prefixes. The prefix “mono-” is used only for the second
element in the name. When there is no prefix, “mono-” is implied, as
in “carbon monoxide.” Also, when “mono-” comes before
“-oxide,” an "o" is dropped. Thus, you write “monoxide,” not
“monooxide.”
Example: Using prefixes correctly, the name of CO is carbon monoxide.
Table 3.4 Prefixes Used to Name Binary Molecular Compounds
Prefix
Number
Prefix
Number
mono-
1
hexa-
6
di-
2
hepta-
7
tri-
3
octa-
8
tetra-
4
nona-
9
penta-
5
deca-
10
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Sample Problem: Names and Formulas of Binary
Molecular Compounds
Problem
Nitrogen and oxygen form a wide variety of different molecular
compounds with different properties. Two examples are described
below. A third is shown in Figure 3.20.
(a) Dinitrogen tetraoxide is used in rocket fuels. What is its
formula?
(b) NO2 is a toxic brown gas that is found in smog in urban areas.
What is its name?
Solution
(a) Nitrogen comes first in the formula, as in the name, because
it is to the left of oxygen in the periodic table. The prefix “di”
tells you that there are 2 nitrogen atoms and the prefix “tetra”
tells you that there are 4 oxygen atoms.
The formula of dinitrogen tetraoxide is N2O4.
(b) Follow these steps to name a compound.
1. Name the leftmost element in
the formula first.
The first element is N (nitrogen).
2. Name the second element,
making sure the name ends with
the suffix “-ide.”
The second element is O (oxygen),
which becomes “oxide.”
3. Add a prefix to each element’s
name to indicate the number
of atoms of each element in a
molecule of the compound. If
the first element would get the
prefix “mono,” do not include
that prefix.
The compound’s name is nitrogen
dioxide.
Figure 3.20 The compound NO acts
to widen blood vessels, which can
lessen chest pain in heart patients. The
patient takes nitroglycerin pills, which
react in the body to form NO.
Apply What is the name of the
compound NO?
The name of NO2 is nitrogen dioxide.
Check Your Solution
Nitrogen is to the left of oxygen on the periodic table, so it appears
first. The prefix “mono-” is implied in “nitrogen” and the prefix
“di-” is correctly used in “dioxide.”
Practice Problems
9. Write the formulas of the following molecular compounds.
(a) sulfur tetrafluoride
(d) oxygen difluoride
(b) disulfur difluoride
(e) nitrogen tribromide
(c) dinitrogen trioxide
(f) diiodine hexachloride
10. Write the names of the following molecular compounds.
(c) SO3
(e) CCl4
(a) PI3
(b) SO2
(d) S2F10
(f) N2O5
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3-2E
Think About It
Decisions, Decisions
Flowcharts can be used to represent a process graphically.
For example, the simple flowchart to the right shows how
to approach solving the problem of what to do when
your morning alarm sounds. Although in practice you do
not need a flowchart to decide whether or not to hit the
snooze button, it can be helpful to use a flowchart to go
through a more complex decision-making process. Writing
a chemical name or formula, for example, requires making
a number of decisions and determinations about the
compound in question.
How can you design flowcharts to represent the
processes of naming and writing formulas for compounds?
What to Do
1. Work in small groups. Your teacher will assign you one
of the following two tasks:
• Design and make a flowchart to represent the
process of naming compounds.
• Design and make a flowchart to represent the
process of writing formulas for compounds.
2. In your group, brainstorm a list of criteria for your
flowchart. What goal should it accomplish? Who
should be able to use it? Have your teacher check and
approve your criteria.
3. As a group, decide what medium you will use to
present your flowchart. You could use software to
create a digital image, for example, or you could draw
your flowchart on a large sheet of paper.
4. As a group, design and make your flowchart. Test it by
using it to name or write formulas for several ionic and
molecular compounds.
5. Share your flowchart with the class.
Morning alarm is going off
Is it summer,
a weekend
or a holiday?
No
Get up and
go to school.
Yes
Get up and
go to work.
Yes
Do you have a
shift at work?
No
Hit the snooze button.
What Did You Find Out?
1. Compare the naming flowcharts from different groups.
What were the similarities and differences? What
worked and what did not work as well?
2. Compare the formula-writing flowcharts from different
groups. What were the similarities and differences?
What worked and what did not work as well?
3. How would you improve your flowchart if you had to
redo this activity?
4. Would making a flowchart for these processes have
been possible without a consistent, logical naming and
formula-writing system? Explain your answer.
IUPAC and Systematic Names
What comes to mind when you hear the word “lime”? You probably just
pictured the small green citrus fruit shown in Figure 3.21. But lime is
also the common name for a hugely important chemical with a broad
variety of applications in farming, the pulp and paper industry, and the
food industry, to name just a few. Chemists working with the compound
lime know that it is an ionic compound composed of calcium and oxygen,
but nothing about its common name suggests that fact. The name calcium
oxide and the formula CaO, however, tell you what you need to know
about the composition of lime.
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Who developed the rules for naming and writing formulas that you
have been learning to use? The international system for naming chemicals
is maintained by the International Union of Pure and Applied Chemistry
(IUPAC). Founded in 1919, IUPAC has developed a systematic method
to name chemicals according to their composition. Today, scientists all
over the world use the IUPAC system. This system ensures that each
pure substance has a unique name, called its systematic name. The name
of a substance describes its composition. It also enables scientists to write
its chemical formula and predict some of its properties.
A
B
Figure 3.21 (A) The word “lime” could mean a tangy fruit. (B) Or, it could refer to the important industrial chemical calcium
oxide, CaO. Common names are still used in industry and on labels, but they do not provide any information about the
composition of the compound.
Communicate What is another example of a word that can mean two different things?
3-2F
Why IUPAC?
Bodies such as IUPAC and the ACS (American Chemical
Society) create and uphold rules for naming elements and
compounds. Before such rules were in place, however,
chemicals were often given evocative names—now called
common or “trivial” names—that emerged from their
appearance, properties, production, or use rather than their
chemical composition.
What to Do
1. Work in groups. Your teacher will assign you one of the
following names: alumina, cinnabar, hematite, laughing
gas, limestone, magnetite, or slaked lime.
2. Conduct Internet research to find out the systematic
name and chemical formula of your compound. List any
additional names for the compound. Also, list some of
its properties, applications, and a few interesting facts
you come across in your research. If possible, find out
the historical source of the common name.
Think About It
3. Present your findings to the class as a poster or
electronic slide presentation.
What Did You Find Out?
1. Was it always clear what compound was meant by the
common or “trivial” name? Explain your answer and
give an example.
2. Give some advantages and disadvantages to using
common names for substances.
3. What are the key advantages of having an
international system of naming and writing formulas
for chemical compounds? Are there any disadvantages?
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Exceptions to the Rules
Did You Know?
Because of its very tiny size
relative to other atoms, and
its single electron, hydrogen is
unusual. It has some properties
that make it similar to the
metals in Group 1, but others
that make it similar to the nonmetals in Group 17. For this
reason, some periodic tables
show hydrogen on its own,
separated from the main groups.
One important group of compounds breaks the naming rules given in
this section. These are the compounds that contain hydrogen. You might
think that HCl, for example, would be ionic. It contains hydrogen (found
with the metals on the periodic table) and a non-metal. In fact, hydrogen
is a non-metal, and HCl is known to be molecular. In its pure form, it is a
gas at room temperature.
Although it is a molecular compound, HCl is not named in the same
way as other molecular compounds you have encountered so far. Like
other binary hydrogen-containing compounds, it is named as though it is
an ionic compound. The correct name for HCl is thus hydrogen chloride,
not hydrogen monochloride. Similarly, the name of H2S is hydrogen
sulfide, not hydrogen disulfide. And these compounds are named
differently when they are dissolved in water. You will learn more about
this type of compound in Chapter 4.
Compounds containing hydrogen and carbon, such as ethane, C2H6,
or ethanol, C2H5OH, have yet another set of naming rules, which you
will encounter if you continue your studies in chemistry.
Key Naming Rules: A Summary
In this section you learned how to name and write the formulas of ionic
and molecular compounds. Table 3.5 below summarizes some of the
key points to remember when naming molecular compounds and ionic
compounds. In the next section, you’ll use your naming and formula
writing skills to describe chemical reactions.
Table 3.5 A Summary of Key Naming and Formula-Writing Rules
Ionic Compounds
Molecular Compounds
Binary Ionic Compounds
Binary Molecular Compounds
• The metallic element (positive ion) comes first in the name
and the formula.
• The end of the name of the non-metallic element is changed
to “-ide” (for example, sodium chloride).
• Ions of multivalent metals are named by adding Roman
numerals in brackets to indicate their charges (for example,
lead(IV) chloride).
• Subscripts in the formulas indicate the ratio of ions of each
type in the compound.
• The total charge of the ions must add to zero.
• The leftmost element on the periodic table comes first
in the name and the formula.
• The suffix "ide" is attached to the name of the second
element.
• These compounds are named using prefixes to indicate
the number of atoms in each molecule (for example,
P2O5 is diphosphorus pentaoxide).
• The prefix “mono-“ is omitted in the first element
named (e.g., CO2 is carbon dioxide).
• Subscripts in the formulas indicate the number of
atoms of each element in each of the compound.
Compounds with Polyatomic Ions
• Refer to Table 3.3 for the names and charges of polyatomic
ions.
• When writing formulas, treat polyatomic ions as a unit.
Include brackets around the formula of the ion if the ion as a
whole takes a subscript.
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Checking Concepts
Understanding Key Ideas
1. Jeremy states that nitrogen dioxide, NO2, is
not a binary compound because it contains
three atoms in the molecule. Is Jeremy
correct or incorrect? Explain your reasoning.
2. Why do people with diets that contain a lot
of fish not suffer from goitres?
3. What ending do all binary compounds
share, whether they are ionic or molecular
compounds?
4. Fiona writes the formula for calcium chloride
as Ca1Cl2. Is this correct? Explain why or why
not.
5. The ratio of calcium to fluorine in calcium
fluoride is 1:2. Based on this, can the ionic
binary compound be written as Ca3F6?
Explain why or why not.
6. Which of the following are binary
compounds?
AlCl3, H2O, CNO, C6H12O6, MgS, PbF2,
NaHCO3, NaOH
7. Write the names of the ionic compounds that
form using the following elements.
(a) silver and chlorine
(b) oxygen and zinc
(c) beryllium and iodine
(d) fluorine and magnesium
8. Identify the charge on the metallic ion in the
following ionic compounds.
(a) PbO2
(b) CuS
(c) CrF3
(d) FeN
9. A test question asks you to write the formula
for iron oxide. What further information do
you need in order to write the compound’s
formula, and how would this information be
indicated in the question?
10. Mercury has the chemical symbol Hg and
can form two ions when forming ionic
compounds. Write and name the two possible
compounds that could form when mercury
combines with oxygen.
11. Two sodium atoms are walking down the
street when one turns to the other and says,
“I lost an electron.” The other says, “Are you
sure?” The first one says, “Yes, I am positive.”
Trailing behind is a magnesium atom, which
proudly announces, “Hey, I am positive too.”
Explain what the ions in this story are really
telling us about the type of ion they form in
ionic compounds.
12. Some people call the method of writing
formulas for ionic compounds “electron
accounting.” Explain why this is a good
name.
13. David states that the name of CuCl2 is
copper(I) chloride while Terri states that the
name is copper(II) chloride. Which is correct?
Explain your answer.
14. Write the formulas for each of the following:
(a) iron(II) nitride (c) copper(I) sulfide
(b) lead(II) oxide
(d) tin(IV) fluoride
15. Write formulas for each of the following:
(a) nitrogen dioxide
(b) sulfur trioxide
(c) dinitrogen tetraoxide
(d) phosphorus pentachloride
16. Name each of the following:
(c) KHCO3
(a) AlPO4
(b) Na2CO3
(d) Mg(OH)2
17. Write formulas for the following:
(a) sodium sulfate
(b) magnesium phosphate
(c) calcium nitrate
(d) aluminum chlorite
18. Write formulas for the following:
(a) copper(I) chlorate
(b) iron(II) phosphate
(c) tin(IV) carbonate
(d) nickel(II) permanganate
Project Prep
Consider the importance of using systematic
names and formulas in the planning and
analysis of a scientific investigation.
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3.3 Chemical Equations and the
Law of Conservation of Mass
What Do You Think?
• How do elements and compounds interact to form different compounds?
• What relationship exists between the mass of substances before and after a
chemical change?
• What ways can you think of to represent a chemical change, and what are the
advantages and disadvantages of each?
Key Terms
chemical reaction
reactant
product
chemical equation
coefficient
chemical reaction a
process in which pure
substances undergo a
change, forming a different
pure substances
Loud explosions, flashes of colour, puffs of smoke—these are all results
you might expect from chemical reactions. Many chemical reactions are
explosive, colourful, and smoky. But many more take place in the world
around you without your even noticing them. However, whether they are
obvious or not, chemical reactions are vital to maintaining and sustaining
your health and the health of all life on Earth. Table 3.6 shows some
examples of chemical reactions.
In chemical terms, a chemical reaction occurs when one or more
substances (elements or compounds) change to form one or more
different substances (elements or compounds). The substances that
undergo a chemical reaction are called the reactants. The substances
formed in a chemical reaction are called products. Look at Table 3.6 and
try to identify the products and reactants for each chemical reaction.
reactant an element or
compound that undergoes
a chemical reaction
product an element or
compound that is formed
in a chemical reaction
128
Table 3.6 Examples of Chemical Reactions
Example
Description
lemon
cake rising
In a leavening reaction, baking soda reacts with
lemon juice to form compounds including carbon
dioxide and water.
fireworks
exploding
In one of many reactions that take place in fireworks,
potassium chlorate reacts to form potassium chloride
and oxygen.
oak tree
performing
photosynthesis
In the reaction that is responsible for producing all
of the oxygen in the air we breathe, plants use
energy from the Sun to convert carbon dioxide and
water into glucose and oxygen.
human
performing
respiration
Everything you do is powered by cellular respiration.
In this energy-releasing reaction in the cells of your
body, oxygen and glucose are converted into carbon
dioxide and water.
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Word Equations
Suggested Activity
Nitrogen and its compounds are an essential part of the biosphere. But
too much nitrogen, or nitrogen in the wrong form, can damage an
ecosystem. For example, too many ammonium-containing compounds
in oceans or lakes can lead to an overgrowth of algae, as shown in
Figure 3.22. The algae use up dissolved oxygen, killing other organisms,
reducing diversity, and making the water unsafe for human use.
As part of a process that can be used to remove excess ammonium
ions from wastewater, special bacteria can convert dissolved ammonium
nitrite to gaseous nitrogen and liquid water. These bacteria are facilitating
a useful chemical reaction.
B
A
Investigation 3-3B: Mass Before
and After
C
Figure 3.22 (A) This algal bloom was caused by pollutants such as excess ammonium-containing compounds. (B) Ammonium-containing
wastewater is produced by a variety of human activities, including farming, mining, and the food industry. (C) Certain bacteria can use a chemical
reaction to clean up ammonium-containing wastewater.
Take a look at the description of a chemical reaction in the previous
paragraph. Is there a more concise way to represent this chemical
reaction? One way is to use the word equation shown in Figure 3.23. In a
word equation, the name of each reactant is written to the left of an arrow
and the name of each product is written to the right of the arrow. If there
is more than one product or reactant they are separated by “” signs as
shown.
“produces”
or
“yields”
“and”
ammonium nitrite → nitrogen � water
reactant
products
Figure 3.23 A word equation is one concise way to represent a chemical reaction.
Identify What type of compound is the reactant? How would you classify the products?
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The Conservation of Mass in Chemical Reactions
The work of early chemists influenced the way chemical reactions are
studied and represented today. In the late 1700s, a French scientist named
Antoine Lavoisier, shown in Figure 3.24, greatly advanced the study
of chemistry. One of his most influential contributions was recognizing
the importance of measuring the mass of all the substances involved in a
chemical change. These measurements were crucial for making accurate
inferences about what happened to the substances.
Lavoisier performed many experiments in which he carefully measured
the mass of the reactants, performed a reaction in a sealed container (a
closed system), and then carefully measured the mass of the products. For
example, he worked with mercury(II) oxide, HgO, which reacts to form
mercury and oxygen when heated. Over and over again, his results were
the same: the total mass of the reactants was the same as the total mass
of the products. He summarized his results in his law of conservation of
mass.
The Law of Conservation of Mass
In a chemical reaction, the total mass of the products is always the
same as the total mass of the reactants.
B
A
Figure 3.24 (A) Antoine and Marie-Anne Lavoisier were a successful scientific team. Marie-Anne
translated scientific papers published in English into French for her husband and drew diagrams of the
setups he used for his experiments. (B) Marie-Anne’s sketches include the closed system apparatus
that Lavoisier used for his experiments that demonstrated conservation of mass.
Conservation of Atoms
Lavoisier’s work allowed John Dalton to re-introduce the idea of atoms
to the world in the early 1800s. Since atoms make up each reactant and
product, Dalton’s atomic theory stated that each atom in the reactants
is also present in the products. Since atoms are neither created nor
destroyed in chemical reactions, the mass does not change, either.
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Chemical Equations and the Law of Conservation of Mass
Scientists use a chemical equation to represent a chemical reaction. A
chemical equation is different from a word equation in that it includes the
formulas for the elements and compounds involved, rather than the names.
chemical equation a
representation of a chemical
reaction that uses chemical
formulas and symbols
Skeleton equation Refer back to Figure 3.23. Replacing the words
in a word equation with chemical formulas produces what is sometimes
called a skeleton equation, shown below. A skeleton equation is still
incomplete, however; it does not reflect the law of conservation of mass.
There are different numbers of atoms of hydrogen and oxygen on each
side of the equation.
coefficient number placed
in front of a chemical
formula in a balanced
equation to show how
many atoms, molecules, or
ions are involved
NH4NO2 → N2  H2O
Balanced chemical equation A balanced chemical equation represents
a chemical reaction as it really occurs. In accordance with the law of
conservation of mass, atoms are never destroyed or created in a chemical
reaction—they are just rearranged. So in a balanced chemical equation,
the same number of atoms of each element appear on both sides of the
arrow. This balance is achieved using coefficients. Coefficients not shown
are assumed to be 1, as in this balanced chemical equation:
NH4NO2(aq) → N2(g)  2H2O(ℓ)
The State of a Substance
As shown in the example above, a chemical equation may also provide
information about the states of the reactants and products in a chemical
reaction. Table 3.7 shows the abbreviations used to do this.
3-3A
Paper Clip Reactions
In this activity, use
paper clips to model
atoms and molecules
to help you balance
chemical equations in
accordance with the
law of conservation of mass.
Materials
• paper clips of different colours
• list of skeleton equations
What to Do
1. Your teacher will give you a list of skeleton equations.
For each, use paper clips to model the reactants and
products. One paper clip of a given colour should
represent one atom of a given element. Note which
colour you are using for each element.
Table 3.7 Abbreviations
for States of Substances
State
Abbreviation
Solid
(s)
Liquid
(ℓ)
Gas
(g)
Dissolved in
water
(aqueous
solution)
(aq)
F i nd Out ACTIV ITY
2. Taking each equation in turn, work with the paper
clip models to create a balanced equation in which
the reactants have the same number of each colour of
paper clip as the products.
What Did You Find Out?
1. What could you do to balance the equation while
maintaining an accurate model of the chemical
reaction? What could you not do and still maintain an
accurate model?
2. How did your paperclip models reflect the conservation
of atoms in chemical equations?
3. What strategies did you use to make it easier to
balance the equations?
4. Were any of the equations particularly easy to balance?
Particularly difficult? Explain why you think this was
the case.
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Balancing Chemical Equations
A
The steps below summarize how to use coefficients to balance chemical
equations. The explosive formation of water from hydrogen and oxygen,
shown in Figure 3.25, is used to illustrate the steps.
How to Balance a Chemical Equation
1. H2(g)  O2(g) → H2O(ℓ)
In the skeleton equation, there is the same number of hydrogen
atoms on both sides of the equation. There are more oxygen atoms
in the reactants, however, than in the product.
B
Checking the Atom Balance
Element
Reactant
Product
Equal?
H
2
2
yes
O
2
1
no
H2O
H2
O2
2. H2(g)  O2(g) → 2H2O(ℓ)
Placing the coefficient 2 in front of H2O(ℓ) balances the oxygen atoms
on each side of the equation. But now there are 4 hydrogen atoms on
the product side and only 2 on the reactant side.
Figure 3.25 A flame (A) is used to
ignite a mixture of hydrogen (in the
balloon) and oxygen in air. In the
resulting explosion (B), water forms.
Checking the Atom Balance
Element
Reactant
Product
Equal?
H
2
4
no
O
2
2
yes
H2
O2
2H2O
3. 2H2(g)  O2(g) → 2H2O(ℓ)
Placing the coefficient 2 in front of H2(g) brings the total number
of hydrogen atoms to 4 on each side of the equation. The equation
is now balanced.
Checking the Atom Balance
132
Element
Reactant
Product
Equal?
H
4
4
yes
O
2
2
yes
2H2 O2
2H2O
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Check Your Understanding
13. Iron reacts with oxygen to form iron(III) oxide. Write a word
equation to describe this reaction.
14. What was the significance of a closed system in Lavoisier’s
experiments?
15. What is the law of conservation of mass?
16. How does a balanced chemical equation reflect the law of
conservation of mass?
17. Determine the number of atoms of each element in the following
terms.
(a) 3CO
(d) 3PCl5
(b) H2O
(e) 2NH4NO3
(c) 5NO2
(f) 2(NH4)2SO4
18. Balance each of the following chemical equations.
(a) Mg(s)  O2(g) → MgO(s)
(b) Li(s)  Br2(g) → LiBr(s)
(c) Al(s)  CuO(s) → Al2O3(s)  Cu(s)
(d) CH4(g)  O2(g) → CO2(g)  H2O(g)
(e) Al(s)  O2(g) → Al2O3(s)
(f) CaCl2(aq)  AgNO2(aq) → AgCl(s)  Ca(NO3)2(aq)
Tips for Writing and Balancing Chemical Equations
When you are writing or balancing a chemical equation, it is important to
remember that every equation is different. The same approach does not
work for every chemical equation. You should be systematic, however, in
the approach you use. A few suggestions to help you get started are listed
below. Keep them in mind as you work through the Practice Problems
on the next page.
• Balance equations by adjusting coefficients, never by changing
chemical formulas.
• Balance metals first.
• Add coefficients to any elements last.
• Balance hydrogen and oxygen last. They often appear in more than
one reactant or more than one product, so it is easier to balance them
after the other elements are balanced.
• If a polyatomic ion appears in both a reactant and a product, treat it
as a single unit.
• Once you think the chemical equation is balanced, do a final check by
counting the atoms of each element one more time.
• If you go back and forth between two substances, using higher and
higher coefficients, double-check each chemical formula. An error
in a chemical formula might be preventing you from balancing the
chemical equation.
• Remember that the following elements exist as diatomic molecules,
like the one in Figure 3.26: hydrogen, H2(g), nitrogen, N2(g),
oxygen, O2(g), fluorine, F2(g), chlorine, Cl2(g), bromine, Br2(ℓ), and
iodine, I2(s).
Figure 3.26 When writing a
chemical equation, always write
oxygen as O2.
Interpret Why would you not write
oxygen as O in a chemical equation?
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Sample Problem: Writing a Balanced Chemical
Equation
Problem
Ammonia is an important fertilizer and is also used in household
cleaners, as shown in Figure 3.27. In the industrial production of
gaseous ammonia, gaseous nitrogen and gaseous hydrogen react to
form the product. What is the balanced chemical equation?
Solution
1. Begin by writing a word equation.
Figure 3.27 You may be familiar
with the sharp smell of ammonia in
glass cleaning products. Ammonia’s
properties make it suitable for
cleaning to a shine.
nitrogen  hydrogen → ammonia
2. Next, write a skeleton equation by writing the chemical formula
for each substance. Remember that nitrogen and hydrogen are
diatomic molecules. Include the states.
N2(g)  H2(g) → NH3(g)
3. Finally, use coefficients to balance the equation.
First consider the compound in the equation, since elements are
easier to balance later. You know you need to have 2 nitrogen
atoms in the product to balance the nitrogen in the reactants.
Therefore, add a coefficient of 2 to NH3(g).
N2(g)  H2(g) → 2NH3(g)
Now the nitrogen atoms are balanced. But the hydrogen atoms
are not balanced, because there are 2 hydrogen atoms on
the reactant side and 6 hydrogen atoms on the product side.
Therefore, add a coefficient of 3 to H2(g).
N2(g)  3H2(g) → 2NH3(g)
Check Your Solution
All the chemical formulas are correct. The atoms all balance, as
shown below.
Element
Reactant
Product
Equal?
N
2
2
yes
H
6
6
yes
Practice Problems
For each of the following reactions, write a word equation, a skeleton
equation, and a balanced chemical equation, including states of matter.
11. Nitrogen monoxide gas reacts with oxygen gas to form
nitrogen dioxide gas.
12. Solid aluminum reacts with oxygen gas to form solid
aluminum oxide.
13. Potassium sulfate and silver nitrate, both dissolved in water,
react to form solid silver sulfate and dissolved potassium nitrate.
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Conduct an InVesTIgATIOn
3-3B Mass Before and After
SkillCheck
• Predicting
• Observing
• Recording
• Analyzing and Interpreting
In this investigation, you will analyze the mass of products and reactants in a
reaction that takes place when you mix two solutions.
Question
How does the mass of the reactants compare with the mass of the products in a
chemical reaction between sodium hydroxide and iron(III) nitrate?
Prediction
Safety Precautions
Make a prediction about how the mass of the reactants will compare to the mass of
the products of the reaction you are about to perform.
Procedure
•
Wear safety eyewear
throughout this activity.
•
Wear a lab coat or apron
throughout this activity.
•
Rinse any spills with plenty
of water, and report them to
your teacher immediately.
•
Dispose of materials as your
teacher instructs.
Materials
•
graduated cylinder
•
dilute sodium hydroxide
solution, 0.1 mol/L NaOH(aq)
•
200 mL Erlenmeyer flask
•
dilute iron(III) nitrate
solution, Fe(NO3)3(aq)
•
small test tube
•
stopper (to fit the
Erlenmeyer flask)
•
balance
1. Read the steps that follow. Make a table to record your results.
2. Use a graduated cylinder to measure 20 mL of dilute sodium hydroxide solution,
NaOH(aq). Pour the solution into the Erlenmeyer flask.
3. Pour the iron(III) nitrate solution, Fe(NO3)3(aq), into the small test tube. Fill the
small test tube about half full.
4. Tilt the Erlenmeyer flask carefully and let the small test tube slide down inside,
as shown in the photograph. Do not let the solutions mix. Seal the flask with
the stopper.
5. Measure the mass of the flask and its contents. Record your measurement. Also
record your qualitative observations about the appearance of the contents of
the flask.
6. Tip the flask so that the solutions mix. Observe what happens and record your
observations.
7. Measure the mass of the flask and its contents. Record your measurement.
8. Follow your teacher’s instructions to dispose safely of the materials and clean
up your work area.
Analyze
1. What did you observe that tells you a chemical reaction took place?
2. The stoppered flask creates a closed system in which no substances can enter
and from which no substances can escape. Why was it important to create a
closed system for this investigation?
3. How did the mass of the reactants, flask, test tube, and stopper compare with
their mass after the reaction?
Conclude and Apply
1. How did your results compare to the prediction you made at the beginning of
the activity?
2. Do you think you would see similar results if you carried out an investigation
like this with different reactants (and different products)? Explain your answer.
3. Propose an explanation for what you observed in this investigation.
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Green Chemistry
Reduction of Waste with Green Chemistry
A relatively new field of chemistry, called green
chemistry, focusses on designing reactions that produce less
waste. These reactions can be used for drug manufacturing
and other industrial processes. Green chemistry also aims
to reduce or eliminate toxic substances that are used in
or produced by many chemical reactions. Some of the
principles of green chemistry include:
• preventing or reducing waste
• using safer solvents
• using renewable raw materials
• ensuring that reactions are energy efficient
Litres of Waste per 1000 kg
of Emend® Produced
The development of new medicinal drugs has great benefits
for humans and other animals. The chemical reactions that
are used to make these drugs, however, often involve many
steps. These steps may result in as much as 100 000 times
more waste than the amount of drug produced, by mass.
The waste can harm the environment, and disposal of
waste can be expensive.
400 000
350 000
300 000
250 000
200 000
150 000
100 000
50 000
0
Before Green
Chemistry
Using Green
Chemistry
The process that involves green chemistry produces 340 000 fewer
litres of waste per 1000 kg of drug produced compared to the
traditional process. This is a huge reduction in waste: 340 000 L of
waste could fill more than 2000 average-sized bathtubs!
Green Medicine
As one example, Merck and Co. Inc. has developed a
greener reaction for synthesizing a drug called Emend®.
This drug is used to treat vomiting and nausea caused by
chemotherapy. The new reaction is far more efficient than
the original reaction. It uses smaller amounts of reactants,
water, and energy to produce twice as much of the desired
product! It also involves fewer steps than the original
reaction. The costs of producing the drug are therefore
reduced.
In the past, chemists who were working to protect
the environment designed ways to clean up the toxic
wastes produced by chemical processes. The goal of green
chemistry is not to create these toxic wastes in the first
place.
Atom economy (AE) is an important principle of green chemistry.
Chemists design reactions to use as little of the reactants as
possible to produce the greatest yield of the desired product. Waste
is therefore reduced. Chemists calculate percent atom economy
using this equation:
(
)
mass of final desired chemical compound
%AE  ________________________________  100%
sum of masess of all reactant compounds
Questions
1. Turn to Appendix B at the end of in this textbook
and read the 12 principles of green chemistry.
Choose one principle. Explain how this principle
helps to protect the environment.
2. Rewrite each of the 12 principle statements for a
class of Grade 7 students so they will be able to
understand the principles of green chemistry.
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Checking Concepts
1. Write word equations for three common
reactions. Label the products and the
reactants.
2. When looking at an equation for a chemical
reaction, what does the arrow mean?
3. Describe the difference between a word
equation and a chemical equation.
4. What is a skeleton equation, and how does it
differ from a balanced chemical equation?
5. When a chemical compound must be placed
in water to form a solution in a reaction, how
is this indicated in the chemical equation?
6. Identify the reactants and products in each of
the following:
(a) Mg(s)  HCl(aq) → MgCl2(aq)  H2(g)
(b) Fe(s)  O2(g) → Fe2O3(s)
(c) Na3PO4  FeCl3 → FePO4  NaCl
(d) MgO(s) → Mg(s)  O2(g)
7. Describe the contribution of Antoine
Lavoisier to the study of chemical reactions.
8. What are the numbers that are placed in
front of a chemical compound to balance a
chemical reaction called?
9. Which elements exist as diatomic molecules?
Understanding Key Ideas
10. As a tree gets older, it increases in mass.
Explain why this is not an exception to the
law of conservation of mass.
11. Your classmate states that the law of
conservation of mass is not being followed
in the reaction of Mg(s)  O2(g) → MgO(s)
because there is a loss of one atom of oxygen
in the process. Is this statement correct or
incorrect? Explain your answer.
12. After balancing the reaction of hydrogen
gas and oxygen gas to form water vapour, a
student balanced the reaction as follows:
4H2(g)  2O2(g) → 4H2O(g)
Is this balanced correctly? Explain your
answer.
13. State the number of atoms of each element in
the following terms:
(c) 3Cu2(SO4)
(a) 2NH4NO2
(d) 4FeCl3
(b) 5H2SO4
14. Write the skeleton equation for each of the
following reactions:
(a) sodium chlorate reacts with potassium
iodide to form sodium iodide and
potassium chlorate
(b) copper(II) sulfate reacts with heat to form
carbon dioxide gas and copper(II) oxide
(c) zinc reacts with copper(II) nitrate to form
copper and zinc nitrate
(d) iron reacts with oxygen to form iron(III)
oxide
15. Which equation from question 14 is not
balanced? Determine the balanced equation
for this reaction.
16. Propane, C3H8, reacts with oxygen to
form carbon dioxide and water during the
combustion process.
(a) Write the skeleton equation for this
reaction.
(b) Balance the reaction.
17. Write balanced chemical reactions for each
word equation. (You do not need to include
states.)
(a) potassium iodide → potassium  iodine
(b) lead(II) nitrate  sodium chloride →
lead(II) chloride  sodium nitrate
(c) magnesium  silver nitrate →
magnesium nitrate  silver
(d) sodium  water →
sodium hydroxide  hydrogen
18. Balance the following skeleton equations:
(a) H2O2(aq) → H2O(ℓ)  O2(g)
(b) Fe(s)  H2SO4(aq) →
H2(g)  Fe2(SO4)3(aq)
(c) FeBr3(s) → FeBr2(s) + Br2(ℓ)
Project Prep
Consider the importance of including balanced
chemical equations as part of the planning and
analysis of a laboratory investigation.
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Chapter
3
Prepare Your Own Summary
In this chapter, you learned how to name and
write formulas for chemical compounds. You also
learned how to write balanced chemical equations
to represent chemical reactions. Create your own
summary of the key ideas from this chapter. You
may include graphic organizers or illustrations or
both for your summary. (See Appendix B for help
with using graphic organizers.) Use the following
headings to organize your summary:
1. Ionic and Molecular Compounds
2. Names and Formulas of Ionic and Molecular
Compounds
3. Chemical Equations and the Law of
Conservation of Mass
Checking Concepts
1. You are probably familiar with the smell of
chlorine from visiting a local swimming pool.
(a) Explain why chlorine compounds are
added to pool water.
(b) After heavy use, municipalities will
“shock” the water in a pool by adding a
larger than normal amount of chlorine.
Why would this be done?
2. How are ionic compounds and molecular
compounds different at the atomic level?
3. Describe three physical properties of ionic
compounds and three physical properties of
molecular compounds.
4. When given the compound S2O5 to name,
Maya said it was called disulfur pentaoxide
while Dennis said that it was called
pentaoxygen disulfide. Who is correct and
why?
5. Consider the order of elements in formulas
of ionic compounds.
(a) In a binary ionic compound, which
element is listed first in the formula, the
positively charged metallic ion or the
negatively charged non-metallic ion?
(b) Is the order the same when writing the
name of the compound?
138
6. What are the small numbers located in some
compound formulas called, and what do they
indicate?
7. Write the ionic compound formulas for each
of the following combinations of atoms.
(a) aluminum and chlorine
(b) lithium and oxygen
(c) sulfur and magnesium
(d) nitrogen and calcium
8. Write names for each of the following:
(a) SO3
(b) N2O5
(c) PCl3
(d) P2O3
9. Explain the steps that must be followed to
determine the formula of calcium nitride.
10. Consider the chemicals that react and form
in chemical changes.
(a) What is the general name given to
chemical compounds that are required to
start a chemical reaction?
(b) What is the general name given to the
chemical compounds that form during a
chemical reaction?
11. What is a multivalent metal? Give three
examples as part of your answer.
12. When you see a Roman numeral in the name
of an ionic compound, what does it tell you
about the metal in the compound?
13. What is the ratio of lithium ions to oxide
ions in lithium oxide?
14. Explain how balancing a chemical equation
reflects the law of conservation of mass.
Understanding Key Ideas
15. Is a family unit more like an ionic compound
or a molecular compound? Explain your
answer.
16. Explain why a binary ionic compound cannot
be formed with lithium and calcium.
17. Determine the charge for each metallic ion in
the following compounds:
(c) TiO2
(a) CuSO4
(b) CrF3
(d) Fe2S3
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18. In which of the following compounds does
iron have a 2 charge?
FeS, Fe3(PO3)2, Fe(OH)2, FeN, FeSO4,
Fe(CH3COO)2, Fe(OH)3
19. Write formulas for each of the following:
(a) tetraphosphorus hexoxide
(b) dinitrogen monoxide
(c) sulfur tetrafluoride
(d) carbon disulfide
20. Write names for each of the following:
(a) SnO
(c) Fe2S3
(b) PbCl2
(d) NiN
21. Write the formulas of each of the following:
(a) iron(II) carbonate
(b) tin(IV) chromate
(c) ammonium phosphate
(d) copper(I) acetate
22. Octane, C8H18, is used in fuels for
automobiles. In the combustion process,
octane combines with oxygen to produce
carbon dioxide gas and water vapour.
(a) Identify the reactants and products in
this process.
(b) Write the skeleton equation for this
reaction.
(c) Balance the skeleton equation.
23. Write skeleton equations for the following
reactions. (You do not need to include
states.)
(a) calcium sulfate  potassium hydroxide →
calcium hydroxide  potassium sulfate
(b) barium  water →
barium hydroxide  hydrogen
(c) copper(I) sulfide  oxygen →
copper(I) oxide  sulfur dioxide
(d) magnesium nitride  water →
magnesium oxide  nitrogen trihydride
24. Balance the skeleton equations from
question 23.
25. Balance the following skeleton equations.
(a) NO2(g)  O2(g)  2H2O(ℓ) →
HNO3(aq)
(b) CH4(g)  O2(g)  Cl2(g) →
HCl(g)  CO(g)
(c) Mg(OH)2(s)  HNO3(aq) →
Mg(NO3)2(aq)  H2O(ℓ)
(d) Na2S(aq)  HBr(aq) →
NaBr(aq)  H2S(g)
26. For each of the following reactions, write a
word equation, a skeleton equation, and a
balanced chemical equation, including states
of matter.
(a) Nitrogen gas reacts with bromine gas to
form gaseous nitrogen tribromide.
(b) Liquid phosphorus trichloride reacts with
chlorine gas to form solid phosphorus
pentachloride.
(c) Aqueous silver nitrate reacts with solid
copper to form aqueous copper(II)
nitrate and solid silver.
27. Baking soda, NaHCO3(s), and citric
acid, C6H8O7(s), react in water to form
carbon dioxide, water, and sodium citrate,
Na3C6H5O7(aq). This is the reaction you
observed if you did the Launch Lab at the
beginning of the chapter.
(a) Sodium citrate is an ionic compound.
What is the charge on the negative ion?
How do you know?
(b) Write a skeleton equation for the
reaction.
(c) Write a balanced chemical equation for
the reaction. Include states of matter.
Why It Matters
The law of conservation of mass states that
matter is not destroyed or created in a chemical
reaction—it stays constant. How does the law
of conservation of mass relate to the three Rs:
reduce, reuse, and recycle? How does it relate
to the principles of green chemistry, described
in the Science Watch in Section 3.3? Since the
quantity of matter on Earth is more or less
constant, what implications does the law of
conservation of mass have for the way we use
natural resources such as oil and gas?
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