MATTER
reflect
You have already learned that matter is the stuff that
everything in the universe is made of. In chemistry,
scientists study matter and the changes associated with
it. For example, water is matter than can exist in three
different states: a solid, a liquid, or a gas. You can freeze
liquid water and it will change into ice (a solid), or you can
heat liquid water and it will evaporate into water vapor (a
gas). What distinguishes these forms of water from one
another, and how do they behave differently?
What makes liquid water
different than ice or water
vapor?
Matter has mass and volume.
Does matter have a more specific definition than simply
“stuff”? Scientists define matter as anything that has mass
and takes up space. Mass is a measure of the amount of matter a substance contains;
volume is the amount of space a substance takes up. Even
gases that you cannot see, like water vapor, have mass and
volume. Like solids and liquids, gases are matter.
A water molecule
consists of an oxygen
atom (O) bonded to two
hydrogen atoms (H).
All matter is made of atoms, the smallest particles of a
substance that still have the properties of that substance.
Atoms combine to form molecules; a molecule consists of
two or more atoms joined by chemical bonds. A molecule of
water always contains two atoms of hydrogen and one atom
of oxygen. This molecule is the same whether in an ice cube,
a drop of liquid water, or a puff of water vapor. When matter
changes state—for example, from solid to liquid or gas—it does
not form different kinds of molecules.
look out!
This sample of boron,
an element, contains
only boron atoms.
Each atom of boron
has five protons.
Do not confuse the terms atom and
element. An atom is an individual
unit of matter. An element is a
substance that contains only one
kind of atom. Scientists have
discovered more than 100 different
elements. All the atoms of an
element contain the same number
of protons.
proton: a positively
charged particle
that, together
with electrons
(negative charge)
and neutrons (no
charge), makes up
an atom
© 2013-2014 Accelerate Learning - All Rights Reserved
1
MATTER
Also do not confuse the terms molecule and compound. A molecule consists of two or more
atoms joined through chemical bonds. A compound consists of two or more elements joined
through chemical bonds. Hydrogen gas (H2) and oxygen gas (O2) are molecules—each
consists of multiple atoms of only one type of element. Water (H2O) and carbon dioxide
(CO2) are both molecules and compounds.
The properties of a substance can change.
Scientists use two types of properties to identify matter: physical and chemical. A
physical property can be observed or measured without changing the matter itself.
Some examples of physical properties of matter include color, smell, melting and
boiling points, magnetism, and density. You can observe the color of water by
looking at it and the smell of water by smelling it. You can measure the melting and
boiling points of water by heating it; you may cause a change of state, but you do not
produce new kinds of matter. You can observe whether water is magnetic by holding a
magnet beside it. You can calculate the density of water by dividing a sample’s mass
(measured using a balance) by its volume (measured using a graduated cylinder).
None of these observations or measurements changes the water into a different kind
of matter.
Wood is a very flammable
substance. Burning wood
produces new substances such
as carbon dioxide and ash.
A chemical property can be observed only when the
matter changes as a result of a chemical reaction. In
other words, you observe chemical properties only
when one type of matter changes into another. Some
chemical properties include reactivity to different
chemicals and flammability. Combining molecules of
two different chemicals—for example, hydrogen and
oxygen—creates molecules of a new chemical: water.
You can observe whether a substance is flammable
by burning it; burning is a chemical reaction that
produces new kinds of substances.
Properties can also be classified based on whether
they change as the amount of matter changes.
Extensive properties depend on the amount of
a substance in a sample. For example, water in a large glass has greater mass and
volume than water in a small glass. It also has more thermal energy—the total energy
of vibrating particles in a substance—because it contains more particles. Mass, volume,
and thermal energy are all extensive properties.
© 2013-2014 Accelerate Learning - All Rights Reserved
2
MATTER
Intensive properties are properties of matter that do not
depend on the amount of a substance present in a sample.
Boiling point, melting point, and density are common
intensive properties. For example, at standard conditions,
liquid water will always boil when it reaches 100°C. This is
true whether you are trying to boil a small cup of water or
a large pot of water. Frozen water (or ice) will always melt
when it exceeds 0°C. This is true whether you are trying to
melt a small ice cube or a large block of ice.
The larger sample of water
has different extensive
properties than the smaller
sample. Both samples
have the same intensive
properties.
Under different conditions, the properties of a substance
can change. During a physical change, the chemical
composition or identity of a substance does not change.
In other words, only the substance’s physical properties
change during a physical change. For example, a physical
change occurs when you break ice into many small pieces. Additionally, all state changes
are physical changes. For example, a physical change occurs when you freeze water to
form an ice cube or when you melt ice to form liquid water.
Alternatively, a chemical change results in the formation of a new substance. In other
words, the substance’s chemical properties change. (These are usually accompanied by
physical changes.) If you dissolve an antacid tablet into water, a chemical change occurs.
The gas bubbling through the water as the tablet dissolves is a sign of this change. The
properties of the gas are different than the properties of the tablet or the water.
what do you think?
The picture on the left shows a measurement of the length of a paper clip. The picture on
the right shows the measurement of the temperature of water in a pipe. Are these physical
or chemical properties? Intensive or extensive properties?
© 2013-2014 Accelerate Learning - All Rights Reserved
3
MATTER
The movement and arrangement of particles is different in solids, liquids, and gases.
The atoms and molecules in matter are in constant motion, but some particles move more
quickly and farther apart than others. Because of this, solids, liquids, and gases have
different properties. Remember that a molecule of a substance (such as water) is the same
whether it is in a solid, liquid or a gas state. State of matter depends
not on the types of molecules that make up a substance but on how
these molecules move and interact.
• Solids: Of the three states of matter, a solid has particles
that move the least. The particles that make up a solid have
relatively little energy. As a result, they are packed closely
together, vibrating slightly in a fixed arrangement. Because the
particles in a solid cannot move very much, solids are relatively
incompressible. In other words, if you press down on a solid,
it does not move as much as a liquid or gas would move. This
arrangement of particles also gives solids a fixed shape and a
specific volume. An ice cube has the same shape and volume
whether it is sitting in a square box, in a round pitcher, or upon a
flat table.
• Liquids: The particles in a liquid are not as closely packed as
the particles in a solid. They have more energy and move freely
around each other. This is why liquids flow and take the shapes
of their containers. However, the particles in a liquid have less
energy than the particles in a gas. As a result, they are still quite
attracted to each other. Liquids are more compressible than
solids but less compressible than gases, and—like solids—a
liquid has a fixed volume. If you pour liquid water into a round
pitcher, the water will take on a round shape. If you pour liquid
water into a square box, the water will take on a square shape.
However, the water will not expand outward to fill the volume of
either container.
The particles
in a solid are
packed closely
together in a fixed
arrangement.
The particles in a
liquid move freely
past each other
but still remain
close together.
© 2013-2014 Accelerate Learning - All Rights Reserved
4
MATTER
• Gases: Of the three states of matter, a gas has particles
with the most energy. Gas particles can move far apart from
each other. As a result, gases have neither fixed shapes nor
fixed volumes. They are very compressible. If you pipe water
vapor into a closed cylinder, the gas will spread out to fill its
container. If you press down on the lid of the container, the
gas will decrease in volume as its particles are forced closer
together. If you have ever watched steam rising from a boiling
pot of water, the steam diffuses—or spreads out—into the
air as the water molecules move as far from each other as
possible.
The particles in a
gas move freely
apart from each
other.
There is a fourth state of matter: plasma. A plasma is similar to a
gas, but it is made up of ionized—or charged—particles. Some
of the particles in a plasma have positive charges, while other particles are free electrons
(in other words, electrons that are not attached to a nucleus). Plasmas are important
components of fluorescent light bulbs, neon signs, and plasma televisions.
look out!
For most types of matter, the particles are more closely
packed in the solid state than in the liquid state. These
solids are denser than the liquids they become when they
melt. (In other words, a sample of the solid contains more
particles than the same volume of liquid.) Water is an
important exception. Molecules of solid water are spaced
farther apart than molecules of liquid water. As a result,
ice is less dense than water. Ice floats on water.
This phenomenon is caused by hydrogen bonds: weak
interactions between the hydrogen and oxygen atoms of
neighboring water molecules. Oxygen atoms have slightly
negative charges, while hydrogen atoms have slightly
positive charges. Recall that opposite charges attract and
like charges repel. When water molecules come together
to form ice, the hydrogen atoms attract the oxygen
atoms and repel the other hydrogen atoms. The result
is a crystal, or lattice, structure with large gaps between
neighboring water molecules.
Hydrogen bonds keep water
molecules apart as they
come together to form ice.
© 2013-2014 Accelerate Learning - All Rights Reserved
5
MATTER
Matter can be a pure substance or a mixture.
A pure substance is matter made up of only one component. Pure substances may contain
only one type of atom (for example, a sample of the element boron) or only one type of
molecule (for example, a glass of water, which contains both hydrogen and oxygen atoms).
Water is also a compound because it contains several different atoms; boron is not a
compound.
In contrast to pure substances, a mixture is a combination of two or more substances
that do not form chemical bonds with each other. Air is a common mixture. Air contains
molecules of nitrogen gas (N2), oxygen gas (O2), and carbon dioxide (CO2), as well as
atoms of argon (Ar) and other elements. Most air also contains molecules of water vapor
(H2O). Air particles flow together in the atmosphere without forming chemical bonds.
Suppose you had a mixture of sugar dissolved in water. Even if you used a magnifying
glass, you would be unable to distinguish the sugar particles from the water particles. In
this type of mixture, the composition is uniform. In other words, each sample of sugar water
contains the same ratio of sugar and water particles. This is an example of a homogeneous
mixture. (Sugar water is not a compound because the sugar and water particles do not form
chemical bonds.) Other homogeneous mixtures include air, gasoline, and metal alloys.
Now, suppose you combined small iron pieces and
grains of sand. Some parts of this mixture would have
more iron pieces, and other parts would have fewer iron
pieces. Because its composition is not uniform, this is
an example of a heterogeneous mixture. In a typical
heterogeneous mixture, you can identify the different
pieces fairly easily. Other examples of heterogeneous
mixtures are oil and water, salad, and granite, a type
of rock.
This sample contains different
types of nuts. Because each
handful contains a different
ratio of nuts, the mixture is
heterogeneous.
Mixtures can be separated into their components using
physical means. If you had a mixture of small iron
pieces and sand, you could pick out the iron by moving
a magnet over the sand. If you had a mixture of sand stirred into water, you could separate
the sand by pouring the water through a filter. Homogeneous mixtures are more difficult to
separate, but you can still use physical means. To separate dissolved sugar from water, you
can heat the water until it evaporates. The liquid water changes to a gas, leaving behind the
sugar particles.
© 2013-2014 Accelerate Learning - All Rights Reserved
6
MATTER
Everyday Life: Heat can cause both physical and chemical changes.
There are many ways to change matter, and these changes may be either physical or
chemical. Heat is often used to cause a change. Consider melting ice cream or butter.
Adding heat is what causes each type of food to melt, or change from solid to liquid. In
these cases, heat causes physical changes.
However, heat can also cause chemical changes. Consider what happens when you cook
an egg. Ordinarily, the insides of an egg—the white and the yolk—are mostly liquid. When
we add enough heat, however, the white and yolk become solid. The heat rearranges the
atoms that make up the egg’s molecules, resulting in new substances.
Before heat is added, an egg’s white and yolk are liquid (left). Cooking the
egg causes a chemical change, resulting in new, solid substances (right).
Another example of how heat can cause both physical and chemical
changes happens when we light a candle. Candle wax is a simple
compound consisting of carbon atoms (C) and hydrogen atoms (H).
As the candle burns, the wax gets hot and melts—a physical change.
At the same time, the carbon and hydrogen in the burning wax
react with oxygen atoms (O) in the air. As a result of this chemical
reaction, the wax changes into carbon dioxide (CO2) and water
(H2O). Because new molecules form, burning a candle also causes
chemical changes.
© 2013-2014 Accelerate Learning - All Rights Reserved
7
MATTER
What do you know?
Matter exists in different forms. Study the types of matter in the box below. Decide whether
each is a pure substance or a mixture. Write your answers in the table below the list. If the
substance is a mixture, identify whether it is a homogeneous or a heterogeneous mixture.
• A glass of iced tea with ice
Types of Matter
• Brewed tea
• Aluminum foil
• Air
• Acetic acid and water
• Dirt
• Brass (an alloy of copper and zinc)
• Distilled water
• Carbon dioxide
• Chicken noodle soup
• Gold
• Milk
Pure substance
Mixture
Homogeneous
Heterogeneous
© 2013-2014 Accelerate Learning - All Rights Reserved
8
MATTER
connecting with your child
Motion in the Three States of Matter
To help your child learn more about how atoms and molecules behave in solids, liquids, and
gases, gather a small glass jar and a collection of small, round objects (such as marbles,
grapes, pom-poms, or ball bearings). Instruct your child to create a table like this:
State of Matter
Solid
Liquid
Gas
Image
Motion (Energy)
Interactions
To illustrate how particles behave in a solid, your child should fill the glass container
completely with the small objects. Your child should draw an image of a solid’s particles in
the second column and describe the motion of the particles in the third column. In the final
column, your child should describe how particles in a solid interact with each other. (You
may shake the glass jar to illustrate how the particles interact.)
Next, your child should remove about one-third of the small objects from the jar and then
shake the jar to illustrate how particles in a liquid move. Your child should also complete
the row of the table for particles in a liquid. Finally, your child should remove nearly all of
the objects from the jar and shake the jar to illustrate how the particles in a gas move. Your
child should also complete the final row of the table for particles in a gas.
Here are some questions to discuss with your child:
• How do neighboring particles interact in a solid? A liquid? A gas?
• How do particles move in a solid? A liquid? A gas?
• How does the energy of the particles in each state differ from each other? The particles
in which state have the greatest energy? How do you know this?
© 2013-2014 Accelerate Learning - All Rights Reserved
9