2.1 Classifying Matter
Each piece of your
clothing has a label that
recommends cleaning
methods. A 100%-cotton
shirt may need to be
ironed after washing. A
cotton and polyester
blend fabric may come
out of the dryer wrinkle
free. There is no cleaning
process that works for all
materials.
2.1 Classifying Matter
Pure Substances
Why are elements and compounds classified
as pure substances?
2.1 Classifying Matter
Pure Substances
A pure substance is matter that always has
exactly the same composition.
• Table salt and table sugar are two
examples of pure substances.
• Substances can be classified into two
categories—elements and compounds.
2.1 Classifying Matter
Pure Substances
Every sample of a given substance has the
same properties because a substance has a
fixed, uniform composition.
2.1 Classifying Matter
Elements
How do mixtures differ from pure
substances?
An element is a substance that cannot be
broken down into simpler substances.
An element has a fixed composition because
it contains only one type of atom.
No two elements contain the same type of atom.
2.1 Classifying Matter
Elements
Examples of Elements
• Some elements are solids at room
temperature. Most soft drink cans are
made from aluminum. Carbon is the
main element in the marks you make
with a pencil.
• The elements oxygen and nitrogen are
the main gases in the air you breathe.
• Two elements are liquids at room
temperature–bromine and mercury.
2.1 Classifying Matter
Elements
Symbols for Elements
Chemists use symbols of one or two
letters to represent elements. The first
letter is always capitalized. If there is a
second letter, it is not capitalized.
• C represents carbon.
• Al represents aluminum.
• Au represents gold. (The Latin name for
gold is aurum.)
2.1 Classifying Matter
Elements
Symbols for Elements
Symbols allow scientists who speak different
languages to communicate without
confusion. For example, nitrogen is azote in
France, stickstoff in Germany, and nitrógeno
in Mexico. But all scientists use N as the
symbol for the element nitrogen.
2.1 Classifying Matter
Elements
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.
Gold
Aluminum
Carbon
Iodine
2.1 Classifying Matter
Compounds
How do mixtures differ from pure
substances?
2.1 Classifying Matter
Compounds
A compound is a substance that is made from two
or more simpler substances and can be broken
down into those simpler substances.
A compound always contains two or more
elements joined in a fixed proportion.
2.1 Classifying Matter
Compounds
The properties of a compound differ from
those of the substances from which it is made.
• Water is composed of the elements hydrogen
and oxygen. 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.
2.1 Classifying Matter
Compounds
Silicon dioxide is a compound found in most lightcolored grains of sand and in crystals of quartz. It is a
colorless, transparent solid. Yet, silicon dioxide is
made from a colorless gas (oxygen) and a gray solid
(silicon). In silicon dioxide, there are always two
oxygen atoms for each silicon atom.
Oxygen
Silicon
Silicon dioxide
2.1 Classifying Matter
Mixtures
How do mixtures differ from pure
substances?
2.1 Classifying Matter
Mixtures
If you make salsa, a recipe can guide you. You
can use exactly the amounts in the recipe, or
you can adjust the ingredients to your own
taste. Salsa is a mixture. Each
batch may be slightly different.
2.1 Classifying Matter
Mixtures
The properties of a mixture can vary
because the composition of a mixture is not
fixed.
• Mixtures can retain some of the properties of their
individual substances.
• The properties of a mixture are less constant than the
properties of a substance.
2.1 Classifying Matter
Mixtures
Mixtures can be classified by how well the
parts of the mixture are distributed
throughout the mixture.
Heterogeneous Mixtures
In a heterogeneous mixture, the parts of
the mixture are noticeably different from one
another.
Homogeneous Mixtures
In a homogeneous mixture, the
substances are so evenly distributed that it
is difficult to distinguish one substance in
the mixture from another.
2.1 Classifying Matter
Mixtures
The sand is a
heterogeneous mixture of
different kinds of grains.
The spoon is stainless
steel, a homogeneous
mixture of iron,
chromium, and nickel.
2.1 Classifying Matter
Mixtures
Do the Contents of Two Cans of Mixed Nuts
Meet FDA Regulations?
According to Food and Drug Administration
(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.
2.1 Classifying Matter
Mixtures
1. Comparing and Contrasting
How are the two brands of
mixed nuts alike? How are
they different?
Answer:
2.1 Classifying Matter
Mixtures
1. Comparing and Contrasting
How are the two brands of
mixed nuts alike? How are
they different?
Answer: Both
brands contain
the same types of
nuts but the
amount of each
type differs.
2.1 Classifying Matter
Mixtures
2. Calculating What is the percent by mass of each
type of nut in each can?
Answer:
2.1 Classifying Matter
Mixtures
2. Calculating What is the percent by mass of each
type of nut in each can?
Answer:
Brand A: 44.2% peanuts, 13.64% almonds,
16.79% Brazil nuts, 13.4% cashews, 5.77%
hazelnuts, and 6.21% pecans
Brand B: 54.8% peanuts, 8.90% almonds, 5.59%
Brazil nuts, 21.06% cashews, 4.82% hazelnuts,
and 4.82% pecans
2.1 Classifying Matter
Mixtures
3. Drawing Conclusions Do the contents of each
can meet the FDA regulations? Explain.
Answer:
2.1 Classifying Matter
Mixtures
3. Drawing Conclusions Do the contents of each
can meet the FDA regulations? Explain.
Answer:
Yes. Both brands contain more than four types of
nuts other than peanuts. The masses are within
the 2% to 80% range.
2.1 Classifying Matter
Mixtures
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?
Answer:
2.1 Classifying Matter
Mixtures
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?
Answer: The ingredients are listed in order by total
mass. The ingredient with the largest mass is
listed first.
2.1 Classifying Matter
Solutions, Suspensions, and Colloids
What is the main difference among
solutions, suspensions, and colloids?
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.
2.1 Classifying Matter
Solutions, Suspensions, and Colloids
Solutions
When substances dissolve and form a
homogeneous mixture, the mixture that forms
is called a solution.
Suspensions
A suspension is a heterogeneous mixture
that separates into layers over time.
2.1 Classifying Matter
Solutions, Suspensions, and Colloids
Colloids
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.
2.1 Classifying Matter
Solutions, Suspensions, and Colloids
These liquids represent three categories of
mixtures.
• Windshield wiper fluid is a solution.
• Muddy water collected from a swamp is a
suspension.
• Milk is a colloid.
2.1 Classifying Matter
Assessment Questions
1. Which of these substances is a compound?
a.
b.
c.
d.
copper
water
oxygen
carbon
2.1 Classifying Matter
Assessment Questions
1. Which of these substances is a compound?
a.
b.
c.
d.
copper
water
oxygen
carbon
ANS: B
2.1 Classifying Matter
Assessment Questions
2. Which of these groups of letters could be used as
a symbol for an element?
a.
b.
c.
d.
HF
Cm
Car
fe
2.1 Classifying Matter
Assessment Questions
2. Which of these groups of letters could be used as
a symbol for an element?
a.
b.
c.
d.
HF
Cm
Car
fe
ANS: B
2.1 Classifying Matter
Assessment Questions
3. Which of the following statements does not apply
to a compound?
a. It is made of two or more elements.
b. It has components that are joined in fixed proportions.
c. It can be separated into components by physical
methods.
d. It can be broken down into elements or other
compounds.
2.1 Classifying Matter
Assessment Questions
3. Which of the following statements does not apply
to a compound?
a. It is made of two or more elements.
b. It has components that are joined in fixed proportions.
c. It can be separated into components by physical
methods.
d. It can be broken down into elements or other
compounds.
ANS: C
2.1 Classifying Matter
Assessment Questions
4. How does a compound differ from a mixture?
a. A compound cannot be broken down into simpler
substances.
b. Compounds can be separated by physical processes
and mixtures cannot.
c. The composition of a mixture cannot vary.
d. A compound is made of two or more elements in fixed
proportion.
2.1 Classifying Matter
Assessment Questions
4. How does a compound differ from a mixture?
a. A compound cannot be broken down into simpler
substances.
b. Compounds can be separated by physical processes
and mixtures cannot.
c. The composition of a mixture cannot vary.
d. A compound is made of two or more elements in fixed
proportion.
ANS: D
2.1 Classifying Matter
Assessment Questions
5. Which of these materials is a heterogeneous
mixture?
a.
b.
c.
d.
air
seawater
sand
steel
2.1 Classifying Matter
Assessment Questions
5. Which of these materials is a heterogeneous
mixture?
a.
b.
c.
d.
air
seawater
sand
steel
ANS: C
2.1 Classifying Matter
Assessment Questions
6. Which of the following can be separated with a
filter?
a.
b.
c.
d.
colloids
compounds
solutions
suspensions
2.1 Classifying Matter
Assessment Questions
6. Which of the following can be separated with a
filter?
a.
b.
c.
d.
colloids
compounds
solutions
suspensions
ANS: D