ALE 5. Classification of Matter
Name
Team No.
CHEM 161 – K. Marr
Section
What’s the difference between a physical property and a chemical property?
What is the difference between a physical change and a chemical change?
The Model
(Reference: section 2.1 in Silberberg 5th ed.)
Matter is defined as anything that has mass and takes up space. An atom is the smallest particle of
matter that can involve itself in a chemical reaction. (Nuclear reactions involve subatomic particles
such as neutrons and/or protons.) All of matter is composed of atoms. Matter can be classified as one
of the following: (1) an element; (2) a compound; (3) a homogeneous mixture (also called a solution);
or (4) a heterogeneous mixture. Examples of these are given in the figures below.
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Na
Figure 1. Atoms of the element sodium, Na. This figure represents a “slice” through a
(very small) crystal of a solid sample of sodium metal. Each sodium atom is depicted as
a circle around “Na.”
Figure 2. Diatomic molecules of the element
chlorine, Cl2. This diagram represents a “freeze
frame” of a gaseous sample of chlorine
molecules moving randomly in a spherical
container. A molecule is two or more atoms
chemically bonded together in a fixed ratio by
mass.
ALE 5 - Classification of Matter – Fall 2008
Figure 3. Molecules of the compound
hydrogen chloride, HCl. This diagram
represents a “freeze frame” of a gaseous
sample of hydrogen chloride molecules
moving randomly in a spherical
container. The chlorine atoms are
larger than the hydrogen atoms.
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Cl-
Na+
Cl- Na+ Cl- Na+
Na+
Cl- Na+ Cl- Na+ Cl-
Cl-
Na+
Na+
Cl- Na+ Cl- Na+ Cl-
Cl-
Na+
Na+
Cl- Na+ Cl- Na+ Cl-
Cl- Na+ Cl- Na+
Cl- Na+ Cl- Na+
Figure 4. The compound sodium chloride, NaCl. This figure represents a slice through
a very small crystal of solid sodium chloride, NaCl.
Figure 5. Two homogeneous mixtures of sodium chloride and water. The white circles without Na+ represent
molecules of water, H2O. When NaCl is added to water, water molecules dissolve (separate) the particles of
sodium chloride to form a homogeneous mixture (solution). This is a freeze frame—all of the particles are in
constant random motion.
Cl- Ag+ Cl- Ag+
Ag+ Cl- Ag+ Cl-
Cl- Ag+
Cl- Ag+ Cl- Ag+
Ag+ Cl-
Ag+ Cl- Ag+ Cl-
ALE 5 - Classification of Matter – Fall 2008
Figure 6.
A heterogeneous mixture
of silver chloride, AgCl
and water. The square
arrays of “Ag+” and “Cl-”
represent crystals of solid
silver chloride. The
empty white circles
without represent
molecules of water, H2O.
This is a freeze frame—
all of the water molecules
are in constant random
motion.
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Figure 7. The classification of matter into mixtures and pure substances
Key Questions
1. What makes one sample of matter an element, another sample a compound, and another a mixture?
Distinguish between an element, a compound, a mixture and a pure substance giving an example of
each that is not found on this handout.
a) element:
b) compound:
c) mixture:
d) pure substance:
ALE 5 - Classification of Matter – Fall 2008
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2. Most of the elements are metals, but some of the nonmetallic elements exist naturally as molecular
species. Use figures 1 and 2 of the model to compare and contrast the metallic element sodium with
the nonmetallic element chlorine. What do they have in common and what is different about them?
3. Are there molecules of sodium chloride within a sodium chloride crystal? Yes or No Circle your
choice and explain your reasoning:
4. What is (are) the difference(s) between a homogeneous mixture and a heterogeneous mixture? Give
an example of each that is not found on this handout.
Exercises
5. Can the relative amounts of the components of a mixture vary? Explain using specific examples to
support your explanation.
6. Can the relative amounts of the components of a compound vary? Explain using specific examples
to support your explanation.
ALE 5 - Classification of Matter – Fall 2008
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7. The tap water found in many areas of the U.S. and other parts of the world leave white deposits
when it evaporates. Is this tap water a mixture or a compound? Explain.
8. Explain the following Statements. Support your explanations with appropriate examples.
a.) The smallest particles unique to an element may be atoms or molecules.
b.) The smallest particles unique to a compound cannot be atoms.
Use the following information to answer questions 9 - 13
Sea water is collected at the beach and found to contain several grains of pure, quartz sand. The mixture
is filtered and the solid sand placed in a vial labeled A. Half the remaining liquid is placed in vial B.
The other half of the liquid is heated till it boils. The gas that escapes is collected and cooled. The
liquid that reforms is placed in vial C. The solid that remains after the boiling is placed in vial D.
Use the following four choices to categorize each sample below:
a.) pure element b.) pure compound c.) homogeneous mixture d.) heterogeneous mixture
9. The original sample
10. The sample in vial A
11. The sample in vial B
12. The sample in vial C
13. The sample in vial D
14. Categorize each of the following as a pure substance, a homogeneous mixture or heterogeneous
mixture.
a.) white grape juice
c.) water with ice cubes
b.) open bottle of beer
d.) fresh garden salad
15. If you have a container with hydrogen gas and oxygen gas in it do you have water? Explain why or
why not.
ALE 5 - Classification of Matter – Fall 2008
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