Section 2.1
2.1 Classifying Matter
1 FOCUS
Objectives
2.1.1
2.1.2
2.1.3
2.1.4
2.1.5
2.1.6
Classify pure substances as
elements or compounds.
Describe the characteristics of
an element and the symbols
used to identify elements.
Describe the characteristics of
a compound.
Distinguish pure substances
from mixtures.
Classify mixtures as heterogeneous or homogeneous.
Classify mixtures as solutions,
suspensions, or colloids.
Key Concepts
Why are elements and
compounds classified as
pure substances?
How do mixtures differ
from pure substances?
What is the main
difference among
solutions, suspensions,
and colloids?
Vocabulary
◆
◆
◆
◆
◆
◆
◆
◆
◆
pure substance
element
atom
compound
heterogeneous
mixture
homogeneous
mixture
solution
suspension
colloid
Reading Strategy
Summarizing Copy the diagram below. As
you read, complete the classification of matter.
Matter
a. ?
Element
Mixture
b. ?
c. ?
d. ?
E
ach piece of clothing sold has a care label, which lists recommended
cleaning methods for the clothing. For a sweater, the instructions
might say to machine wash the sweater using a gentle cycle, and then
tumble dry at a low temperature. They might say to hand wash the
sweater in cold water and lay the sweater flat to dry. The label might
even say, “Dry clean only.”
Why is it necessary to put care instructions on a label? The same
cleaning method will not work for all materials. For example, a shirt
made from 100 percent cotton may need to be ironed after washing.
But a shirt made from a cotton and polyester blend may come out of
the dryer wrinkle free. A wool jacket often needs to be dry cleaned
because wool can shrink when washed in water.
The tendency to wrinkle when washed is a property of cotton.
The tendency not to wrinkle when washed is a property of polyester. The tendency to shrink when washed is a property of wool.
Cotton, wool, and polyester have different properties because
they have different compositions. The word composition
comes from a Latin word meaning “a putting together,” or
the combining of parts into a whole. Based on their compositions, materials can be divided into pure substances
and mixtures.
Reading Focus
Build Vocabulary
L2
Paraphrasing To help students
understand the definitions of vocabulary terms, you may replace less familiar
words in a definition with a more familiar
word or phrase. For example, you can
replace distributed in the definition of a
homogeneous mixture with “spread
out,” or shattering in the definition of
malleability with “breaking into pieces.”
Reading Strategy
L2
a. Substance b. Compound
c. and d. Homogeneous mixture or
heterogeneous mixture
2 INSTRUCT
Figure 1 You can use the care labels on clothing to
sort laundry into batches for cleaning. The care
label shown is for a wool sweater that needs to be
dry cleaned or washed by hand.
L2
Some students may associate the term
material exclusively with solids because
they can see and hold solid materials.
They may have difficulty recognizing
that liquids and gases are also matter.
Challenge this misconception by pointing to the Materials list for the lab on
p. 60 and asking students to identify
the liquids.
Verbal
38 Chapter 2
38 Chapter 2
Section Resources
Print
• Reading and Study Workbook With
Math Support, Section 2.1
• Math Skills and Problem Solving
Workbook, Section 2.1
• Transparencies, Chapter Pretest and
Section 2.1
Technology
• Interactive Textbook, Section 2.1
• Presentation Pro CD-ROM, Chapter Pretest
and Section 2.1
• Go Online, NSTA SciLinks, Mixtures
Pure Substances
Pure Substances
FYI
Matter that always has exactly the same composition is classified as a
pure substance, or simply a substance. Table salt and table sugar are
two examples of pure substances. Every pinch of salt tastes equally
salty. Every spoonful of sugar tastes equally sweet.
Every sample of
a given substance has the same properties because a substance has
a fixed, uniform composition. Substances can be classified into two
categories—elements and compounds.
Samples of pure substances almost
always contain impurities, some that
are unintentional, some intentional.
For example, table salt is not pure
sodium chloride. It contains between
0.006% and 0.01% potassium iodide.
Elements
Elements
Although there are millions of known substances, there are only about
100 elements. An element is a substance that cannot be broken down
into simpler substances. Imagine cutting a copper wire into smaller
and smaller pieces. Eventually you would end up with extremely tiny
particles called copper atoms. An atom is the smallest particle of an
element.
An element has a fixed composition because it contains
only one type of atom.
No two elements contain the same type of atom. In Chapter 4, you
will find out more about atoms, including how the atoms of one element differ from the atoms of every other element.
Figure 2 Aluminum, carbon, and
gold are elements that you can
see in common objects, such as
cans, pencils, and rings. Mixtures
containing iodine are used to
prevent and treat infections.
Analyzing Data Which of these
elements has a symbol that is not
related to its name in English?
FYI
Sometimes an atom is defined as “the
smallest particle of an element that has
the properties of the element.” However,
an atom of copper has none of the properties associated with bulk copper, such
as malleability, ductility, or density.
Build Science Skills
Examples of Elements At room temperature (20°C, or 68°F),
most elements are solids, including the elements aluminum and
carbon. You have seen aluminum foil used to wrap food. Most soft
drink cans are made from aluminum. Carbon is the main element in
the marks you make with a pencil on a piece of paper. Some elements
are gases at room temperature. The elements oxygen and nitrogen are
the main gases in the air you breathe. Only two elements are liquids at
room temperature, bromine and mercury, both of which are extremely
poisonous. Figure 2 shows four elements and their symbols.
Iodine (I)
L2
Observing Have students look at the
elements in Figure 2. Ask, What are
some characteristics of the elements
in Figure 2? (Gold is yellow and shiny.
Aluminum is gray and shiny. Carbon is dull
and black. Iodine is a dark purple solid.)
Follow up on their observations by asking
students to hypothesize about why the
iodine sample is in a closed container. (At
room temperature, iodine evaporates and
forms a purple gas, which is visible in the
container. The gas is poisonous.)
Visual
Aluminum (Al)
Gold (Au)
Carbon (C)
Properties of Matter 39
Customize for English Language Learners
Sharing Experiences
Encourage multilingual students to describe
what a particular element is called in their
native language. This exercise will be most
useful for those elements that have been
known for centuries or millennia. (Examples
include carbon, mercury, sulfur, iron, copper,
tin, zinc, silver, gold, and lead.) Use this
information as a springboard for discussing
the element names given in the text.
Answer to . . .
Figure 2 Gold
Properties of Matter 39
Section 2.1 (continued)
Integrate
Language Arts
Symbols for Elements In 1813, Jöns Berzelius, a Swedish
L2
Silicon
Have students research and explain the
origin of element symbols (other than
Au) that are not abbreviations for element names in English. Examples include
silver (Ag), lead (Pb), tin (Sn), antimony
(Sb), and mercury (Hg).
Verbal, Portfolio
Compounds
FYI
When the terms element, atom, compound, and molecule are defined in an
introductory section, the definition of
a molecule is often both too broad
and too narrow. Molecules are not the
smallest particle of all compounds,
and many elements exist in nature as
molecules. For this reason, in this text,
the formal definition of molecule does
not appear until Chapter 6, the chapter
on bonding, where it can be defined
accurately. (The term molecule is
introduced informally in Section 3.3
when water molecules are described.)
chemist, suggested that chemists use symbols to represent elements.
Many of the symbols he assigned to elements are still used. Each symbol
has either one or two letters. The first letter is always capitalized. If there
is a second letter, it is not capitalized.
It is easy to see why C and Al are used to represent carbon and aluminum. But why does gold have the symbol Au? The symbols that
Berzelius chose were based on the Latin names of the elements. The
Latin name for gold is aurum.
The symbols allow scientists who speak different languages to communicate without confusion. For example, nitrogen is known as azote
in France, as stickstoff in Germany, and as nitrógeno in Mexico. But scientists who speak English, French, German, and Spanish all agree that
the symbol for the element nitrogen is N.
Sometimes an element’s name contains a clue to its properties. For
example, the name hydrogen comes from the Greek words hydro and
genes, meaning “water” and “forming.”
Compounds
Oxygen
Figure 3 Elements have different
properties than their compounds.
Silicon is a gray solid and oxygen is
a colorless gas, which can be
stored in a metal tank. Silicon and
oxygen combine to form silicon
dioxide—a colorless, transparent
solid found in most grains of sand.
Silicon
dioxide
Water is composed of the elements hydrogen and oxygen. When electricity passes through water, bubbles of oxygen and hydrogen gas form
and rise to the surface of the water. If the gases are collected in a container and a flame is brought near the mixture, the hydrogen and
oxygen react and form water. Water is classified as a compound. A
compound is a substance that is made from two or more simpler substances and can be broken down into those simpler substances. The
simpler substances are either elements or other compounds.
The properties of a compound differ from those of the substances
from which it is made. For example, oxygen and hydrogen are gases at
room temperature, but water is a liquid. Hydrogen can fuel a fire, and
oxygen can keep a fire burning, but water does not burn or help other
substances to burn. In fact, water is one of the substances commonly
used to put out fires.
Figure 3 shows another example of how properties change when
elements join and form compounds. Silicon dioxide is a compound
found in most light-colored grains of sand. It is a colorless, transparent
solid. Yet, silicon dioxide is made from a colorless gas (oxygen) and a
gray solid (silicon). Silicon is used to make chips for computers.
A compound always contains two or more elements joined in
a fixed proportion. For example, in silicon dioxide, there are always two
oxygen atoms for each silicon atom. (Di- means “two.”) In water, there
are always two hydrogen atoms for each oxygen atom.
What happens if electricity passes through water?
40 Chapter 2
Facts and Figures
Electrolysis of Water Early chemists
were able to use heat to break down many
compounds into their constituent elements.
Because water cannot be decomposed by this
method, water was classified as an element
until chemists were able to use electric current
40 Chapter 2
to break down water into hydrogen and
oxygen. (The decomposition of water into
hydrogen and oxygen will not occur unless
ions are added to the water because there are
not enough ions in pure water to conduct
an electric current.)
Mixtures
Figure 4 The ingredients shown
are used to make one kind of
salsa, which is an example of a
heterogeneous mixture.
Salsa
oes
um tomat
• 4 or 5 pl
Serrano
sh
fre
5
• 3–
s
chili pepper
of cilantro
s
rig
sp
12
•
c clove
• large garli
ite onion
• small wh
1 teaspoons
•1 2
juice
fresh lime
•
teaspoon
salt
3
4
Figure 5 Sand is a heterogeneous mixture. The spoon
is stainless steel, which is a
homogeneous mixture.
Interpreting Photographs
Explain how viewing sand
through a hand lens helps show
that sand is a heterogeneous
mixture.
L1
Compare and Contrast Refer to
page 226D in Chapter 8, which provides the guidelines for comparing
and contrasting.
Have students read pp. 41–44 and gather
information on different classifications of
mixtures. Then, have students create a
chart that compares and contrasts each
type of mixture.
Visual
Integrating
Language Arts
Mixtures
Suppose you are making salsa using the ingredients shown in Figure 4.
You have a choice. You can use exactly the amounts listed in the recipe,
or you can adjust the ingredients according to your own taste. You
might have to prepare the recipe a few times before deciding if you
have just the right amount of each ingredient.
Mixtures tend to retain some of the properties of their individual
substances. But the properties of a mixture are less constant than the
properties of a substance.
The properties of a mixture can vary
because the composition of a mixture is not fixed. The type of pepper
and the quantity of pepper used in a salsa recipe determine the “hotness” of a batch of salsa. Chili peppers contain a compound called
capsaicin (kap SAY uh sin) that can cause a burning sensation in your
mouth. The amount of capsaicin varies among types of peppers.
Cayenne peppers, for example, contain more capsaicin than do
jalapeño peppers.
No matter how well you stir a batch of salsa, the ingredients
will not be evenly distributed. There may, for example, be
more onion in one portion of the salsa than another.
Mixtures can be classified by how well the parts of the mixture are distributed throughout the mixture.
Build Reading Literacy
L2
Have students consider the difference
between hot food (as in warm versus
cold) and hot food (as in spicy versus
mild). Encourage students to suggest
examples of dishes other than salsa
that are hot in the second, spicy sense.
Some students may want to record a
family recipe for a “hot” dish. Have
them identify the ingredient(s) that
can be varied to control the “hotness”
of the mixture.
Logical
Build Science Skills
L2
Observing Have students look at
samples of sand with a hand lens. Explain
that the composition of sand can vary
from beach to beach because the rocks
and shells from which sand forms have
different compositions. Ask, How can
you tell that sand is a heterogeneous
mixture? (The grains of sand vary in color
and size.) (A sample of sand that contains
only ground-up shells would probably be
classified as homogeneous.)
Visual
Heterogeneous Mixtures If you look at a handful
of sand from a beach, the sand appears to be all the same
material. However, if you use a hand lens, you will notice that the
sample of sand is not the same throughout. Figure 5 shows that grains
of sand vary in size. Also, some grains are light in color and some are
dark. Sand is an example of a heterogeneous mixture. Heterogeneous
(het uh roh GEE nee us) comes from the Greek words hetero and genus,
meaning “different” and “kind.” In a heterogeneous mixture, the parts
of the mixture are noticeably different from one another.
Properties of Matter 41
Facts and Figures
Capsaicinoid Content Capsaicin (8-methylN-vanillyl-6-nonenamide) is the most abundant
of a group of compounds called capsaicinoids.
These compounds are found in the seeds and
membranes of chili peppers. When they are
ingested, they affect pain receptors in the
mouth and throat. Because capsaicin is an oil,
and oil and water do not mix, drinking water
spreads the oil to more parts of the mouth
and increases the burning sensation.
The capsaicinoid content of a pepper is
measured in Scoville units. Wilbur Scoville
developed the method for measuring the
“hotness” of chili peppers in 1912. He mixed
ground chilies with a sugar and water solution
and diluted the mixture until tasters no longer
reported a burning sensation. The greater the
dilution needed, the higher the assigned
number of Scoville units. Fifteen Scoville units
is equivalent to one part per million.
Answer to . . .
Figure 5 More details are visible
in the magnified sand, making it
easier to observe the different parts
of the mixture.
Bubbles of oxygen and
hydrogen form and rise
to the surface of the water.
Properties of Matter 41
Section 2.1 (continued)
Do the Contents of Two
Cans of Mixed Nuts
Meet FDA Regulations?
Contents of Two Cans of Mixed Nuts
Do the Contents of Two Cans
of Mixed Nuts Meet FDA
Regulations?
L2
Answers
1. Both brands contain the same six
types of nuts, but the amount of each
type of nut varies.
2. There are 344.79 g in Brand A and
350.32 g in Brand B. The percents by
mass in Brand A are: 44.2% peanuts,
13.64% almonds, 16.79% Brazil nuts,
13.4% cashews, 5.77% hazelnuts,
and 6.21% pecans. The percents by
mass in Brand B are: 54.8% peanuts,
8.90% almonds, 5.59% Brazil nuts,
21.06% cashews, 4.82% hazelnuts, and
4.82% pecans.
3. Yes. Both brands contain more than
four types of nuts other than peanuts.
The percent of each nut by mass is within
the 2% to 80% range.
4. The ingredients are listed in order by
total mass. The ingredient with the
largest total mass is listed first.
For Extra Help
The Food and Drug Administration (FDA) has two
main areas of concern about food. First, and most
important, the FDA ensures that food sold in the
United States is safe to eat. Second, the FDA
ensures that the information on a food label
accurately describes a food product.
What can you assume when you see the label
“mixed nuts” on a can of nuts? According to the
FDA regulations, a can labeled mixed nuts must
contain at least four types of shelled nuts other
than peanuts. The mass of each type of nut must
be not less than 2 percent of the total mass and
not more than 80 percent of the total mass.
Mass in
Brand A
Mass in
Brand B
Peanut
152.39 g
191.96 g
Almond
47.02 g
31.18 g
Brazil nut
57.88 g
19.60 g
Cashew
46.20 g
73.78 g
Hazelnut
19.90 g
16.90 g
Pecan
21.40 g
16.90 g
1. Comparing and Contrasting How are
the two brands of mixed nuts alike? How
are they different?
2. Calculating What is the percent by mass of
each type of nut in each can?
3. Drawing Conclusions Do the contents of
each can meet the FDA regulations? Explain.
4. Inferring On the Brand A label, the nuts
are listed in this order: peanuts, Brazil nuts,
almonds, cashews, pecans, and hazelnuts.
What do you think determines the order?
Homogeneous Mixtures If you collect water from both the
shallow end and the deep end of a swimming pool, the water samples
will appear the same. The water in a swimming pool is a homogeneous
(hoh moh GEE nee us) mixture of water and substances that dissolve in
water. In a homogeneous mixture, the substances are so evenly distributed that it is difficult to distinguish one substance in the mixture
from another. A homogeneous mixture appears to contain only one
substance. The serving spoon in Figure 5 is made of stainless steel—a
homogeneous mixture of iron, chromium, and nickel.
L1
Have students answer Question 3 by calculating 2% and 80% of each total mass
and checking to see if any of the masses
fall outside that range.
Logical
Solutions, Suspensions, and Colloids
It isn’t always easy to tell a homogeneous mixture from a heterogeneous
mixture. You may need to observe the properties of a mixture before you
decide. The size of the particles in a mixture has an effect on the properties of the mixture.
Based on the size of its largest particles, a
mixture can be classified as a solution, a suspension, or a colloid.
Solutions, Suspensions,
and Colloids
Solutions If you place a spoonful of sugar in a glass of hot water
FYI
Many alloys are not true solutions.
Sterling silver, a mixture of silver and
copper, is an example. Silver and copper
are completely soluble in all proportions
when molten. However, solid sterling
silver is a two-phase alloy with pockets
of silver and pockets of a 71.9% silver
and 28.1% copper mixture.
Type of Nut
For: Links on mixtures
Visit: www.SciLinks.org
Web Code: ccn-1021
and stir, the sugar dissolves in the water. The result is a homogeneous
mixture of sugar and water. When substances dissolve and form a
homogeneous mixture, the mixture that forms is called a solution.
The windshield wiper fluid in Figure 6 is a solution. So is tap water.
42 Chapter 2
Facts and Figures
Download a worksheet on
mixtures for students to complete,
and find additional teacher support
from NSTA SciLinks.
42 Chapter 2
Regulatory Agencies Responsibility for
protecting the food supply is shared among
the FDA, the Department of Agriculture, and
the EPA, which regulates pesticides. Food
that is adulterated or mislabeled may be
voluntarily destroyed or recalled, or seized
by court order. The FDA is responsible for
establishing standards for identity, quality,
and fill of container. If standards have been
set for a product, such as mixed nuts, the
product must comply with those standards.
Food labels must include a statement of
identity (usual or common name), the net
quantity of the contents, the name and
place of business of the supplier, and a
list of ingredients in descending order by
mass. The goal is to have honest and
informative labels.
A
Figure 6 The liquids shown represent
three categories of mixtures. A Windshield
wiper fluid is a solution. B Muddy water
collected from a swamp is a suspension.
C Milk is a colloid.
Comparing and Contrasting Based on
appearance, how are a solution and a
colloid similar?
Transmission Versus
Scattering
L2
Purpose Students observe light pass
through different mixtures.
B
C
Materials 2 beakers, water, iodine
solution, table salt, stirring rods, milk,
fish tank, flashlight, white paper
Procedure Demonstrate that a
solution can have color and still transmit
light. Fill two beakers halfway with
water. Add a small amount of iodine
solution to one beaker and stir. Add
table salt to the second beaker. Ask
students to describe the color of each
mixture and state whether it is clear.
Demonstrate transmission of light versus
scattering. Fill the tank with water. Turn
off the lights. Shine a flashlight through
the tank so that it lights up the white
paper placed behind the tank. Add
some milk to the water and stir. Shine
the light through the tank again. (These
behaviors of light are discussed in detail
in Section 18.3.)
Liquid solutions are easy to recognize. They do not separate into
distinct layers over time. If you pour a liquid solution through a filter,
none of the substances in the solution are trapped in the filter. You can
see through solutions that are liquids because light passes through
them without being scattered in all directions. These three properties
of liquid solutions can be traced to the size of the particles in a solution. The particles in a solution are too small to settle out of the
solution, be trapped by a filter, or scatter light.
Suspensions Have you ever seen the instruction “Shake well
before using” on a bottle? This instruction is a clue that the material in
the bottle is a suspension. A suspension is a heterogeneous mixture
that separates into layers over time. For example, if you shake up a container of sand and water, the sand mixes with the water and forms a
suspension. Over time, the suspended particles of sand settle to the
bottom of the container.
You could use a filter to separate the sand from the water. The water
would pass through the filter, but the sand would remain in the filter
paper. Suspended particles settle out of a mixture or are trapped by a
filter because they are larger than the particles in a solution. The
worker in Figure 7 is using a mask to filter out particles of plastic foam
that are suspended in air. Because larger particles can scatter light in all
directions, suspensions are cloudy.
Expected Outcome Although the
salt solution is colorless and the iodine
solution is colored, both transmit light.
Light passes through the water in the
tank and makes a bright spot on the
paper. With milk added, the light is
scattered so that the spot is much
less distinct.
Visual
What happens to suspended particles over time?
Figure 7 When a surfboard is
sanded, particles of plastic
become suspended in air. The
worker wears a mask to keep
from breathing in the particles.
Properties of Matter 43
L1
Use Visuals
Figure 7 To emphasize that suspended
particles settle out over time, ask, What
will happen to the particles of plastic
suspended in the air? (The particles
will eventually settle out.) Discuss with
students the dangers of inhaling
suspended particles. Ask, How does a
mask prevent the worker from inhaling particles of plastic? (The particles in
suspensions can be separated by filtration.
The mask is a filter.)
Visual
Answer to . . .
Figure 6 The solution and the colloid
both appear homogeneous.
Suspended particles
settle out of a mixture.
Properties of Matter 43
Section 2.1 (continued)
Build Science Skills
L3
High beam
Classifying Have interested students
research categories of colloids such as
gels, foams, aerosols, and emulsions.
Have students find out how scientists
distinguish different types of colloids.
Have them identify household examples
of each type.
Visual, Portfolio
3 ASSESS
Evaluate
Understanding
L2
Have students make a game of concentration using the terms in the chapter
and their definitions. Have groups of
students write each term on separate
index cards and the definition of each
term on a second set of index cards. To
play the game, students should shuffle
all the cards together and then lay them
face down in a grid. Each student takes
turns flipping over two index cards. If
the cards match, the student can remove
the cards from the grid. If the cards do
not match, the student places the cards
face down. After all of the cards are
gone, the student who has removed
the most cards wins the match.
Reteach
L1
Use Figure 6 as a visual aid to summarize
the key differences among different
types of mixtures.
Students should specify which
ingredients are required for the cereal to
qualify for a particular label and suggest
a range for ingredients such as dried
fruit or nuts. (Students could choose
another edible mixture, such as canned
vegetable soup.)
Low beam
Figure 8 The photograph shows
how water droplets in fog scatter
the light from high beams. The
drawing compares the areas lit by
high beams and low beams.
Interpreting Diagrams Which
beams normally make a larger
area of a road visible?
Colloids Milk is a mixture of substances including water, sugar, proteins, and fats. When fresh cow’s milk is allowed to stand, a layer of
cream rises to the top. This layer contains much of the fat in the milk.
In the milk you buy at the store, the cream does not form a separate layer.
The milk has been processed so that the fat remains dispersed throughout the milk. The result is homogenized milk, which is a colloid.
A colloid contains some particles that are intermediate in size
between the small particles in a solution and the larger particles in a
suspension. Like solutions, colloids do not separate into layers. You
cannot use a filter to separate the parts of a colloid.
Fog is a colloid of water droplets in air. Figure 8 shows how fog
affects which headlights a driver uses. Automobiles have headlights
with low beams for normal driving conditions and high beams for
roads that are poorly lit. With the high beams, a driver can see a bend
in the road or an obstacle sooner. But the high beams are not useful on
a foggy night because the water droplets scatter light back toward the
driver and reduce visibility. With the low beams, much less light is scattered. The scattering of light is a property that can be used to
distinguish colloids and suspensions from solutions.
Section 2.1 Assessment
Reviewing Concepts
1.
Why does every sample of a given
substance have the same properties?
2.
Explain why the composition of an
element is fixed.
3.
4.
5.
Describe the composition of a compound.
Why can the properties of a mixture vary?
On what basis can mixtures be classified
as solutions, suspensions, or colloids?
Critical Thinking
6. Predicting If you added salt instead of sugar
to a pitcher of lemonade, how would this
change the properties of the lemonade?
7. Interpreting Visuals Explain why silicon
dioxide cannot be the only compound in the
sample of sand shown in Figure 5.
8. Inferring Fresh milk is a suspension. After
fresh milk is homogenized, it is a colloid. What
happens to the size of the drops of fat in milk
when milk is homogenized?
Writing Instructions Pick a cereal that is
an obvious mixture. Write rules that could be
used to control the cereal’s composition. Use
the FDA rules for mixed nuts as a model.
44 Chapter 2
If your class subscribes to
the Interactive Textbook, use it to
review key concepts in Section 2.1.
Section 2.1
Answer to . . .
Figure 8 High beams
44 Chapter 2
Assessment
1. A pure substance has a fixed composition.
2. An element contains only one kind of atom.
3. Compounds contain two or more elements
joined in a fixed proportion.
4. Because the composition of a mixture is
not fixed
5. Mixtures can be classified as solutions,
suspensions, or colloids based on the size
of their largest particles.
6. The lemonade would taste salty instead
of sweet.
7. Silicon dioxide is colorless. There must be at
least one other compound in the sample to
account for the dark-colored grains.
8. Large drops are broken down into smaller
drops, which can remain dispersed
throughout the milk.