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
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
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
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
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
2.2 Physical Properties
There are pitchers of ice water and lemonade
on a picnic table. How do you know which
liquid is in each pitcher? It’s easy! Lemonade
is yellow and has a tart taste that is hard to
miss. A yellow color and a tart taste are two
properties of lemonade.
2.2 Physical Properties
Examples of Physical Properties
What are some examples of physical
properties?
A physical property is any characteristic of a
material that can be observed or measured
without changing the composition of the
substances in the material.
Viscosity, conductivity, malleability,
hardness, melting point, boiling point, and
density are examples of physical properties.
2.2 Physical Properties
Examples of Physical Properties
Viscosity
The tendency of a liquid to
keep from flowing is called its
viscosity.
• Thick liquids, such as corn
syrup and honey, have a high
viscosity.
• Thin liquids, such as vinegar
and water, have a low
viscosity.
2.2 Physical Properties
Examples of Physical Properties
Conductivity
A material’s ability to allow heat to flow
is called conductivity.
• Materials that have a high conductivity,
such as metals, are called conductors.
• Good conductors of heat are usually also
good conductors of electricity.
2.2 Physical Properties
Examples of Physical Properties
Malleability
The ability of a solid to be hammered without shattering is
malleability.
• Most metals, such as gold, are malleable.
• An ice cube or piece of glass breaks into small pieces when
struck with a hammer. Solids that shatter when struck are brittle,
not malleable.
2.2 Physical Properties
Examples of Physical Properties
Hardness
One material can scratch another material if it
is harder than the other material.
• A kitchen knife can scratch a copper sheet
because stainless steel is harder than copper.
• The material used to sharpen the knife blade
must be harder than stainless steel. Diamond is
the hardest known material.
2.2 Physical Properties
Examples of Physical Properties
This Tlingit carver is using an adze to carve a canoe from
Western red cedar. Red cedar is a relatively soft wood.
The adze is hard.
2.2 Physical Properties
Examples of Physical Properties
Melting and Boiling Points
The temperature at which a material changes
state is a physical property.
• The temperature at which a substance changes
from solid to liquid (melts) is its melting point.
• The temperature at which a substance changes
from liquid to gas (boils) is its boiling point.
2.2 Physical Properties
Examples of Physical Properties
Melting and Boiling Points
Which of these substances are liquids
at room temperature (20C, or 68F)?
Answer:
2.2 Physical Properties
Examples of Physical Properties
Melting and Boiling Points
Which of these substances are liquids
at room temperature (20C, or 68F)?
Answer: octane,
water, and
acetic acid
2.2 Physical Properties
Examples of Physical Properties
Density
The ratio of the mass of a substance to its
volume is its density.
• Density can be used to test the purity of a
substance.
• Silver has a density of 10.5 g/cm3. A coin with a
density of 9.9 g/cm3 is not made from silver, or it
contains substances in addition to silver.
2.2 Physical Properties
Using Physical Properties
How can knowing the physical properties of
matter be useful?
Physical properties are used to identify a
material, to choose a material for a specific
purpose, or to separate the substances in a
mixture.
2.2 Physical Properties
Using Physical Properties
Using Properties to Identify Materials
A material can be identified by its
properties.
• Decide which properties to test.
• Do tests on a sample of the unknown
material.
• Compare the results with the data reported
for known materials.
2.2 Physical Properties
Using Physical Properties
Using Properties to Choose Materials
Properties determine which materials are
chosen for which uses.
• For example, shoelaces must be flexible,
that is they must be able to bend without
breaking.
• They must also be durable, that is, they
must be able to withstand repeated use.
2.2 Physical Properties
Using Physical Properties
Laces in hiking boots are usually made of
nylon or leather, not from wood.
2.2 Physical Properties
Using Properties to Separate Mixtures
What processes are used to separate
mixtures?
Filtration and distillation are two common
separation methods.
2.2 Physical Properties
Using Properties to Separate Mixtures
Filtration
You can separate hot tea from loose tea
leaves by pouring the mixture through a
strainer. Filtration is a process that
separates materials based on the size of
their particles.
2.2 Physical Properties
Using Properties to Separate Mixtures
These students filter (sift) dirt through a
wire screen to locate small objects.
Particles of dirt are small enough to pass
through the holes, but objects such as
broken bits of pottery are too large.
2.2 Physical Properties
Using Properties to Separate Mixtures
Distillation
Sometimes all the particles in a solution
are small enough to pass through a filter.
Distillation is a process that separates
the substances in a solution based on
their boiling points.
2.2 Physical Properties
Recognizing Physical Changes
The change of water from a liquid to a gas
during boiling is a physical change. A
physical change occurs when some of the
properties of a material change, but the
substances in the material remain the same.
2.2 Physical Properties
Recognizing Physical Changes
During a physical change, the size and
shape of a material can change but not the
composition. Some examples include
• melting butter in a pan
• crumpling a piece of paper
• slicing a tomato
2.2 Physical Properties
Recognizing Physical Changes
Some but not all physical changes can be
reversed. Braiding hair is a reversible
change. Cutting hair cannot be reversed.
2.2 Physical Properties
Assessment Questions
1. Which of the following is not a physical property?
a.
b.
c.
d.
density
boiling point
flammability
conductivity
2.2 Physical Properties
Assessment Questions
1. Which of the following is not a physical property?
a.
b.
c.
d.
density
boiling point
flammability
conductivity
ANS: C
2.2 Physical Properties
Assessment Questions
2. Which of these materials is not malleable?
a.
b.
c.
d.
copper
aluminum
glass
gold
2.2 Physical Properties
Assessment Questions
2. Which of these materials is not malleable?
a.
b.
c.
d.
copper
aluminum
glass
gold
ANS: C
2.2 Physical Properties
Assessment Questions
3. In choosing a material for use as a wire to carry
electric current, which physical property would be
most important?
a.
b.
c.
d.
conductivity
malleability
hardness
boiling point
2.2 Physical Properties
Assessment Questions
3. In choosing a material for use as a wire to carry
electric current, which physical property would be
most important?
a.
b.
c.
d.
conductivity
malleability
hardness
boiling point
ANS: A
2.2 Physical Properties
Assessment Questions
4. Which of these statements best describes a physical
change in a pure substance?
a. The substance changes into one or more new substances.
b. Some of the properties of the substance change, but the material
remains the same.
c. The properties of the material do not change, and the material
remains the same.
d. The substance is separated into two or more simpler substances.
2.2 Physical Properties
Assessment Questions
4. Which of these statements best describes a physical
change in a pure substance?
a. The substance changes into one or more new substances.
b. Some of the properties of the substance change, but the material
remains the same.
c. The properties of the material do not change, and the material
remains the same.
d. The substance is separated into two or more simpler substances.
ANS:
B
2.2 Physical Properties
Assessment Questions
1. The process of filtration uses the difference in
boiling points of substances to separate a mixture.
True
False
2.2 Physical Properties
Assessment Questions
1. The process of filtration uses the difference in
boiling points of substances to separate a mixture.
True
False
ANS:
F, distillation
2.3 Chemical Properties
How would you describe
these candles? Color,
hardness, and density
are physical properties
that you can use in the
description. You can also
say that the candles are
burning. The ability to
burn is not a physical
property. As a candle
burns, new substances
form.
2.3 Chemical Properties
Observing Chemical Properties
When can chemical properties be observed?
2.3 Chemical Properties
Observing Chemical Properties
As a candle burns, its compounds
combine with oxygen in the air to form
water and carbon dioxide.
A chemical property is any ability to
produce a change in the composition of
matter. Flammability and reactivity are
two examples of chemical properties.
2.3 Chemical Properties
Observing Chemical Properties
Chemical properties can be observed only
when the substances in a sample of matter
are changing into different substances.
2.3 Chemical Properties
Observing Chemical Properties
Flammability
Materials that burn can be used as fuel.
Flammability is a material’s ability to burn in
the presence of oxygen.
Reactivity
The property that describes how readily a
substance combines chemically with other
substances is reactivity.
2.3 Chemical Properties
Observing Chemical Properties
Rust forms when oxygen reacts with iron and water.
Rust is a brittle, reddish-brown compound. Because
iron is highly reactive, you would not choose iron to
make jewelry or coins.
2.3 Chemical Properties
Observing Chemical Properties
Nitrogen has many uses that depend on
its low reactivity.
Researchers in Japan pump nitrogen
gas into the steel tanks that hold
seawater in ships. The nitrogen
displaces the oxygen dissolved in the
water and prevents rusting.
2.3 Chemical Properties
Recognizing Chemical Changes
What observations might indicate that a
chemical change has occurred?
Three common types of evidence for a
chemical change are a change in color, the
production of a gas, and the formation of a
precipitate.
2.3 Chemical Properties
Recognizing Chemical Changes
The color change in a banana peel is caused by
chemical changes that are taking place in the cells
of the banana. A chemical change occurs when a
substance reacts and forms one or more new
substances.
2.3 Chemical Properties
Recognizing Chemical Changes
A Change in Color
A change in color is a clue that a
chemical change has produced at least
one new substance.
• A shiny silver bracelet that is exposed to
air will darken.
• As a match burns, it shrivels up and turns
black.
• A new copper roof and an old copper roof
have different colors.
2.3 Chemical Properties
Recognizing Chemical Changes
A new copper roof has a reddish color.
The green patina on an old copper roof is
a mixture of copper compounds.
2.3 Chemical Properties
Recognizing Chemical Changes
Production of a Gas
When you mix vinegar with baking soda, bubbles of
carbon dioxide form immediately. A similar chemical
change happens when you use baking powder as an
ingredient in a cake recipe. Bubble of carbon dioxide
expand and cause the cake to rise.
2.3 Chemical Properties
Recognizing Chemical Changes
Formation of a Precipitate
Any solid that forms and separates from a liquid
mixture is called a precipitate. When an acid is
added to milk, proteins in the milk undergo a
chemical change that causes them to stick together
in clumps and form a precipitate–cottage cheese.
2.3 Chemical Properties
Is a Change Chemical or Physical?
What is the difference between chemical and
physical changes?
2.3 Chemical Properties
Is a Change Chemical or Physical?
Are different substances present after a
change takes place? If not, then the
change is physical, not chemical.
When matter undergoes a chemical change,
the composition of the matter changes.
When matter undergoes a physical change,
the composition of the matter remains the
same.
2.3 Chemical Properties
Is a Change Chemical or Physical?
Even if you observe a color change, a gas, or a
precipitate, you cannot be sure that a chemical change
has taken place. When an iron horseshoe is heated, its
color changes from gray to red, but the iron is still iron.
That means the change is physical, not chemical.
2.3 Chemical Properties
Assessment Questions
1. Which of these properties is a chemical property
of sulfur?
a.
b.
c.
d.
yellow
flammable
brittle
soft
2.3 Chemical Properties
Assessment Questions
1. Which of these properties is a chemical property
of sulfur?
a.
b.
c.
d.
yellow
flammable
brittle
soft
ANS: B
2.3 Chemical Properties
Assessment Questions
2. Which of the following is not a common type of
evidence for a chemical change?
a.
b.
c.
d.
a change of state
a color change
a gas produced
a precipitate formed
2.3 Chemical Properties
Assessment Questions
2. Which of the following is not a common type of
evidence for a chemical change?
a.
b.
c.
d.
a change of state
a color change
a gas produced
a precipitate formed
ANS: A
2.3 Chemical Properties
Assessment Questions
3. You can be certain that a chemical change has
occurred when
a.
b.
c.
d.
there is a visible change.
the change is irreversible.
the temperature changes.
a new substance is formed.
2.3 Chemical Properties
Assessment Questions
3. You can be certain that a chemical change has
occurred when
a.
b.
c.
d.
there is a visible change.
the change is irreversible.
the temperature changes.
a new substance is formed.
ANS: D