Classification of Matter
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Printed: May 21, 2014
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C HAPTER
Chapter 1. Classification of Matter
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Classification of Matter
Lesson Objectives
• Distinguish between gases, liquids, and solids. Explain how these states differ at the molecular level.
• Classify samples of matter as pure substances, homogeneous mixtures, heterogeneous mixtures, compounds,
and elements.
• Use sketches to show how elements, compounds, and mixtures differ at the molecular level.
• Describe six different techniques for separating mixtures.
• Relate the names of elements to their international element symbols.
• Name the major groups and regions on the periodic table and identify elements belonging to these groups.
• Distinguish between metals, nonmetals, and metalloids using the periodic table.
Lesson Vocabulary
• pure substances: Have a constant composition and can only be changed by chemical reactions.
• elements: Substances that cannot be decomposed into simpler substances by chemical or physical means.
• compounds: Substances that can be broken down into their individual elements, but only through chemical
processes.
• mixtures: A combination of two or more pure substances.
• homogeneous mixtures: A mixture with uniform composition throughout.
• heterogeneous mixtures: A mixture with visibly distinguishable components, exist primarily in the solid and
liquid states.
Check Your Understanding
• Give some examples of chemical properties and physical properties of matter.
• What would be some chemical and physical properties of the following substances:
– a glass of water
– aluminum foil
– argon
Introduction
As we studied in our last lesson, matter can be described by its physical and chemical properties. We have seen
examples of how matter exhibits specific physical and chemical properties, which can be used to distinguish one
type of matter from another. In this lesson, we are going to use these properties to categorize the various forms of
matter.
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States of Matter
Matter typically exists in one of three states: solid, liquid, or gas. The state of a given substance is a physical
property. Some substances exist as gases at room temperature (such as oxygen and carbon dioxide), while others
(like water and mercury metal) exist as liquids. Most metals exist as solids at room temperature. All substances can
exist in any of these three states.
Water is a very common substance that we frequently encounter in all three states of matter, as seen in Figure 1.1.
When water is in the solid state, we call it ice, while water in the gaseous state is referred to as steam or water vapor.
The physical state of matter is a physical property because the identity of a pure substance does not change when it
is melted, frozen, or boiled.
FIGURE 1.1
Water is the same substance in any of
its three states. (A) A frozen waterfall in
Hungary. (B) The Nile River in Egypt. (C)
A steam powered train in Wales.
Solid
A solid is a form of matter that has a definite shape and volume. The shape of a solid does not change if it is
transferred from one container to another. The particles of a solid are packed tightly together in fixed positions,
usually in an orderly arrangement. Solids are almost completely incompressible, meaning that solids cannot be
squeezed into a smaller volume. When a solid is heated or cooled, it expands or contracts only slightly.
Liquid
A liquid is a form of matter that has a definite volume, but an indefinite shape. As water is poured from one container
into another, it adopts the shape of its new container. However, the volume of the water does not change, because
the water molecules are still relatively close to one another in the liquid state. Unlike a solid, the arrangement of
particles in a liquid is not rigid and orderly. Liquids are also incompressible.
Gas
A gas is a form of matter that has neither a definite shape nor a definite volume. A gas takes up the shape and volume
of its container. This is because the particles of a gas are very far apart from one another compared to the particles
that make up solids and liquids. Gases are easily compressed because of the large spaces in between gas particles.
Gas particles are often invisible, but they can be detected in various ways, such as the light emitted when an electric
current is passed through a sample of a gas ( Figure 1.2).
Molecular View of Solids, Liquids, and Gases
We are quite familiar with the properties of solids, liquids, and gases from our everyday experience. These properties
are fundamentally based on differences in the arrangement of atoms or molecules at the microscopic level. Figure
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Chapter 1. Classification of Matter
FIGURE 1.2
Sodium vapor lamps glow with a distinctive yellow color.
1.3 shows the differences between the ways in which particles appear in each of these three states. Remember, any
substance can be present as a gas, liquid, or solid when placed under specific conditions.
FIGURE 1.3
The particles of a gas are very far apart
compared to the particles of a liquid or a
solid.
As Figure 1.3 shows, the distance between particles is much smaller for the solid and liquid states than for the gas
state. In the solid state, particles are fixed in place, while particles are more free to move in the liquid and gas states.
The particles in the solid and liquid states “stick together,” but in the gas state, they move freely about the container.
In general, it requires energy to separate individual particles. If we want to make a solid adopt a liquid form, we
can add energy in the form of heat, increasing the temperature of the substance. Conversely, if we want to convert
a substance from a gas to a liquid or from a liquid to a solid, we remove energy from the system and decrease the
temperature. Pressure also plays an important role in changes of state, which will be discussed later on. We will
study these difference in greater detail in the chapter States of Matter.
Pure Substances
When studying the different states that matter exhibits, we have been looking at pure substances. Pure substances
have a constant composition and can only be changed through chemical reactions. Constant composition indicates
that a sample of a pure substance always contains the same elements in the same proportions. There are two main
types of pure substances:
• elements: Substances that cannot be decomposed into simpler substances by chemical or physical means.
• compounds: Substances that can be broken down into elements through chemical means.
Figure 1.4 shows pure substances in the form of elements and compounds.
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FIGURE 1.4
Pure substances: (left) the element sulfur
and (right) the compound water.
The image on the left shows elemental sulfur in the solid state. The image on the right shows water in its liquid form.
Sulfur is a pure element, and water is a compound comprised of the elements hydrogen and oxygen. Both of these
substances have a constant composition, but water can be broken down into its elements, whereas sulfur cannot be
decomposed into a simpler substance. Water can be broken down into its elements by passing electricity through a
salt solution.
Periodic Table of Elements
Chemists have classified and organized all of the known elements into what is called the periodic table. All known
substances are made of some combination of these elements. The periodic table is a tool that we use to help identify
and describe the composition of a given substance. All pure substances which cannot be broken down further, which
we have called elements, are displayed in the periodic table. Figure 1.5 shows our modern periodic table. We will
study the periodic table in more detail in the chapter The Periodic Table.
Mixtures
When two or more pure substances are combined together, a mixture is formed. Unlike pure substances, mixtures
have a variable composition. Variable composition indicates that the relative proportions of the mixtures components
may vary, and they can be separated by physical methods. There are two main types of mixtures.
Homogeneous Mixtures
A homogeneous mixture is one in which the composition is uniform throughout the mixture. A glass of salt water
is a homogeneous mixture because the dissolved salt is evenly distributed throughout the entire sample. It is often
easy to confuse a homogeneous mixture with a pure substance because they are both uniform, and it can be difficult
to tell which type you have by the naked eye. The difference is that the composition of the pure substance is always
the same, while the composition of a homogeneous mixture can vary. For example, you may dissolve a small amount
or a large amount of salt into a given sample of water. Although the ratio of salt to water will differ, the mixtures
will both be homogeneous. However, pure water will always have the same ratio of elements that make it a pure
substance (two hydrogen atoms per oxygen atom).
Wine, air, and gunpowder are other examples of common homogeneous mixtures ( Figure 1.6). Their exact
compositions can vary, making them mixtures rather than pure substances. Wine is a liquid mixture of water,
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Chapter 1. Classification of Matter
FIGURE 1.5
The modern periodic table.
ethanol, and a variety of other dissolved substances. Air is a mixture of nitrogen gas (78%), oxygen gas (21%), and
small amounts of various other gases. Gunpowder is a solid mixture comprised of potassium nitrate (75%), charcoal
(15%) and sulfur (10%).
FIGURE 1.6
Examples of homogenous mixtures: wine
and gunpowder.
In this figure, we see that the components of these mixtures cannot be distinguished from one another. However, the
substances comprising these mixtures can be separated through physical means.
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Heterogeneous Mixtures
Heterogeneous mixtures have visibly distinguishable parts. These mixtures will typically exist in the solid or liquid
states, but not the gas state. Gas state heterogeneous mixtures are not possible because gas particles freely mix and
disperse. Heterogeneous mixtures are quite common. For example, oil-and-vinegar salad dressing is a heterogeneous
mixture that is in the liquid state. Its composition varies and typically includes olive oil mixed with red vinegar. An
example of a solid heterogeneous mixture is soil. Soil is primarily comprised of organic and inorganic material,
including substances like decaying plants and animals, minerals, water, and air. The composition of soil varies
greatly from one location to another. Figure 1.7 shows these mixtures.
FIGURE 1.7
Examples of heterogeneous mixtures:
(left) oil and vinegar and (right) soil.
The substances that comprise heterogeneous mixtures can also be separated by physical means. We will discuss
separation techniques in the following lesson.
Lesson Summary
• Matter exhibits specific physical and chemical properties.
• Matter can exist in one of three states: solid, liquid, or gas.
• In the solid state, particles are fixed in place relative to one another. In the liquid and gas states, individual
particles are free to move.
• Under the right pressure conditions, lowering the temperature of a substance in the gas state causes the
substance to liquefy. The opposite effect occurs if temperature is increased.
• Under the right pressure conditions, lowering the temperature of a substance in the liquid state causes the
substance to solidify. The opposite effect occurs if the temperature is increased.
• Pure substances have a constant composition and can only be changed by chemical reactions. They can be
classified as either elements or compounds.
• Elements are substances that cannot be decomposed into simpler substances by chemical or physical means.
Compounds, however, can be broken down further through chemical, but not physical, means.
• The periodic table is a tool that we use to help identify and describe the composition of a given substance. The
table is an arrangement of elements based on their physical and chemical properties.
• Homogeneous or heterogeneous mixtures are formed when two or more pure substances are combined. A
homogeneous mixture has a uniform distribution throughout the sample, whereas a heterogeneous mixture
has visibly distinguishable components.
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Chapter 1. Classification of Matter
Review Questions
1. Compare and contrast the three states of matter. Try to describe similarities and differences apparent at a
microscopic level as well as at the observable level between these states of matter.
2. Which of the following would be an example of a pure substance?
a.
b.
c.
d.
plastic
milk
100% ethanol
cake flour
3. Which of the following would be an example of an element?
a.
b.
c.
d.
water
orange juice
steel
iron
4. Which of the following would be an example of a compound?
a.
b.
c.
d.
water
sulfur
aluminum
brass
5. Compare and contrast a pure substance with a mixture and give an example.
6. Which of the following statements is true?
a.
b.
c.
d.
The periodic table is a list of various compounds found throughout the world.
The periodic table is randomly organized.
The periodic table has been the same for 50 years.
The periodic table is an organized assembly of the various elements that have been discovered.
7. Classify the following as a homogeneous mixture, a heterogeneous mixture, or neither.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
powdered sugar
mayonnaise
scrambled egg
air
soda pop
concrete
apple juice
glass
steel
copper
Further Reading / Supplemental Links
• Examples of laboratory techniques used for separating mixtures can be found at Science Park: http://scien
cepark.etacude.com/projects/
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Points to Consider
• As we saw, compounds can be broken down into their elemental components. How might you go about
breaking down a compound into its elements?
• The components that comprise homogeneous and heterogeneous mixtures can be separated out by physical
means. How might you go about separating out components of a soil mixture?
References
1. (A) Rodrigo; (B) Christine und David Schmitt (Flickr:cheesy42); (C) Steven Whateley. (A) http://commo
ns.wikimedia.org/wiki/File:Lillafured_icedwaterfall_wman.jpg; (B) http://commons.wikimedia.org/wiki/File
:Nile_river_at_Luxor_2007.jpg; (C) http://commons.wikimedia.org/wiki/File:Steam_Train.JPG . (A) CC BY
2.5; (B) CC BY 2.0; (C) Public Domain
2. User:Proton02/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:LPS_Lamp_35W_running.jpg
. Public Domain
3. Christopher Auyeung. CK-12 Foundation . CC BY-NC 3.0
4. Sulfur: Hi-Res Images of Chemical Elements; Water: Claire Cessford. Sulfur: http://commons.wikimedia
.org/wiki/File:Sulfur_%2816_S%29.jpg; Water: http://www.flickr.com/photos/35137234@N06/4230612281/
. Sulfur: CC BY 3.0; Water: CC BY 2.0
5. User:Cepheus/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:Periodic_table.svg . Public
Domain
6. Wine: George Hodan; Gunpowder: Oliver H.. Wine: http://www.publicdomainpictures.net/view-image.php
?image=35183&picture=glass-of-red-wine; Gunpowder: http://commons.wikimedia.org/wiki/File:Spk-RZ.jpg
. Public Domain
7. Oil/vinegar: Kat (Flickr:tyger_lyllie); Soil: Petr Kratochvil. Oil/vinegar: http://www.flickr.com/photos/ty
ger_lyllie/3350276971/; Soil: http://www.publicdomainpictures.net/view-image.php?image=13200&picture
=soil-texture . Oil/vinegar: CC BY 2.0; Soil: Public Domain
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