States of matter
verything around you is made of matter. Anything that has mass and takes up
space is matter. The air we breathe, the water we drink and the food we eat are
all different types of matter. But air, water and food are very different. One
important difference between these items is their state.
Solids do not usually flow
The three main states of matter are solid, liquid and gas.
Most solids are too rigid to flow.
E
Substances such as sugar, which
are made up of many small solid
pieces, can be poured.
Gases change shape
Gases fill the entire container they
are in. The helium gas in balloons
changes shape depending on the
shape of the balloon. The helium fills
every part of the balloon.
The volume of gases changes
Gases expand to fill the
containers they are placed
in. Gases do not have a
fixed volume.
Solids have a constant
shape
Solids have a fixed shape
and change shape only
when a force is applied.
The force applied to both
ends of this bar by the
circus strongman causes
the bar to bend.
Gases flow
Like liquids, gases
flow from one
container to another.
The gas from the
helium bottle flows to
the balloon through a
tube. It is often hard to
see gases flow because
many of them are
colourless.
Gases can be compressed
Gases can be squeezed so they
take up less space (compressed).
The gas inside the helium bottle
is compressed. It expands when
it leaves the bottle and fills the
balloons. Solids and liquids
cannot be compressed.
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Science Alive for VELS Level 5
Investigating solids, liquids and
gases
You will need:
a piece of dowel
large plastic syringe
water
plasticine
salt
sponge.
• Copy the following table.
Liquids have a fixed volume
The liquid from the jug can
be poured into several
glasses. The total amount of
space taken up in the glasses
equals the amount that was
originally in the jug.
Property
Solid (dowel)
Liquid (water)
Gas (air)
Fixed shape
Liquids flow
Liquids can be
poured from
one container
to another.
When the
container is
full, it
overflows.
Solids have a fixed volume
If you move a solid from container
to container, the amount of space it
takes up (volume) is the same.
Fixed volume
Able to be
compressed
• Insert the dowel into the syringe. Press down on the plunger.
1. Can the dowel be compressed?
• Draw some water into the syringe. Put your finger over the end of
the syringe and press down on the plunger.
2. Can water be compressed?
• Draw some air into the syringe. Put your finger over the end of the
syringe and press down on the plunger.
3. Can air be compressed?
• Complete the remainder of the table by looking closely at the dowel
and water, and by reading the captions on the circus scene.
• Investigate the properties of plasticine, salt and sponge.
4. Classify each of the three materials as a solid, liquid or gas.
5. Which materials did you have trouble classifying? Why?
REMEMBER
1. What properties do we use to
classify materials into the three
states?
2. Which state/s of matter:
(a) can be compressed?
(b) can flow?
THINK
3. Classify each of the following
items as a solid, liquid or gas.
Oxygen
Talcum powder
Glass
Vaseline
Oil
Honey
Wood
Sand
4. Why is a bicycle frame made
of solids?
23
2. Solids, liquids and gases
5. Why are bicycle tyres filled
with air?
OBSERVE
6. Look carefully at the circus
scene on the left.
(a) List as many solids,
liquids and gases as you
can find.
(b) Find one example of a
substance that can
change from one state to
another.
✓ learning
Liquids change shape
A liquid’s shape
changes to fit the
container it is in. The
shape of the lemonade
in these glasses depends
on the shape of the
glass. Liquids at rest
have a flat surface.
I CAN:
name the three states of matter
describe the properties of the
three states of matter
classify materials as solids, liquids
or gases.
The particle model
ll matter is made up of tiny particles. If you could shrink down to microscopic
size and watch these particles, you would see that the particles behave
differently depending on whether the substance they make up is a solid, liquid or
gas. To help explain this different behaviour, scientists have developed a model
called the particle model of matter.
A
Models help people understand complex ideas, such
as how matter behaves. As new clues about matter
have been discovered, the models have been
improved. The basis of the particle model is that:
• All matter is made up of small particles.
• Particles are always moving.
• Particles are held together by bonds that vary in
strength.
• As particles are heated, they move more quickly.
When the particles are cooled, they move more
slowly.
Particles in a gas
The forces between the particles in a gas are very weak.
The particles are in constant motion. This means that
gases have no fixed shape or volume. There are large
spaces between the particles. The spaces allow
the gas to be compressed. A gas can flow and
diffuse easily since its particles are always
moving. Gas particles have much more energy
than solid and liquid particles. They move
around and collide with other particles
and the walls of the container they
are in.
Particles in a solid
Solids cannot be compressed
because the particles inside them
are held closely together. There is
no space between them. Bonds also
hold the particles tightly together in
a rigid crystal-like structure. This gives solids their fixed
shape and constant volume. The particles in solids cannot
move freely; they vibrate in a fixed position. This means that
solids are unable to flow.
Particles in a liquid
The particles in a liquid are close together. So, there is no
room for compression between the particles in a liquid. The
particles are also held tightly by bonds, but not in the same
rigid structure as solids. This gives liquids their fixed
volume, but allows the particles to roll over each other.
This rolling allows liquids to flow. The
movement of the particles explains
why liquids take the shape of their
container. The particles roll over each
other until they fill the bottom of the
container.
26
Science Alive for VELS Level 5
Diffusion
Investigating diffusion
Diffusion is the spreading of one substance
through another. The spreading occurs because
the particles of each substance become mixed
together. The movement of the particles in liquids
and gases makes diffusion possible. As the particles
in a gas move faster than in
liquids, diffusion happens
faster in a gas. Particles
are not free to move in
a solid, so diffusion
cannot occur at all.
You will need:
500 mL beaker
water
straw
potassium permanganate crystals
fragrant spray
protective mat
safety glasses.
• Using the straw as a
Hold
straw
guide, put a crystal of
potassium permanganate
in the bottom of a beaker of
water. Remove the straw
and record your
observations.
Crystal
Water
Beaker
1. Draw a diagram of the
movement of the potassium
permanganate through the
water.
REMEMBER
1. What is the basis of the particle model?
2. What is diffusion?
3. Give an everyday example of diffusion at
work.
2. How do you think the fragrant spray moved
through the air?
3. This experiment shows diffusion in a liquid (water)
and diffusion in a gas (air).
(a) Which state diffuses faster — liquid or gas?
(b) Why do you think this is?
Property
Solid
Liquid
Gas
Particle arrangement
Force of attraction between
particles
4. Copy and complete the table at right.
THINK
5. Why do solids have a fixed shape?
6. Why can gases be compressed?
7. Why do gases fill their containers?
8. When you pour cordial into water, the two
Movement of particles
Ability to diffuse
liquids slowly mix together even though
you don’t stir them. Explain how this
happens.
27
2. Solids, liquids and gases
✓ learning
Air deodoriser
• Release some of the fragrant spray in one corner of
the classroom. Move away and observe by smell.
The spreading
starts in an area
where there is a
concentration of
one of the
substances. The
particles keep
mixing through
until they are
evenly spread
through each
other.
I CAN:
describe the particle model of matter
describe how the particles move in
each of the states: solid, liquid and
gas
explain how diffusion occurs in
liquids and gases.
Change of state and
the particle model
magine a very cold day. On days like this, you probably sit inside without moving
around too much. As the weather gets warmer, you start to move around a little
more. On warm, sunny days, you probably have a lot more energy. On these days,
you might feel like moving about more. Much like you, the particles inside matter
also change the way they move when they are heated or cooled.
I
Changing state
A change of state involves the heating or cooling of
matter. As a substance is heated, energy is transferred
to it. When a substance cools, energy moves away from
it to another substance or to the environment. The
change in energy causes the particles in the substance
to move at different speeds.
Solid
When a solid is heated, its
particles start to move more
quickly. The increased
movement of its particles
makes the solid expand.
Melting
As more heat is transferred to the
solid, its particles vibrate more
violently. Eventually the particles
move so much that the bonds
holding them in their fixed positions
break. The particles start to roll
over each other. Melting continues
until the entire solid becomes a
liquid.
Gas
As in solids and liquids, the particles
in gases move faster and faster when
they are heated. The increased
movement of the particles means that
they take up more space and the gas
expands. If the gas is heated in a
closed container, the increased
movement of the particles means that
they collide more often with the sides
of the container and with each other.
Liquid
As a liquid is
heated, its
particles move
and roll over
each other
faster and
faster. The
liquid begins
to expand.
Boiling
If the liquid continues to be heated,
the particles will eventually have
enough energy to break the bonds
holding them together. The particles
can break away from the liquid and
begin to move around freely. This
process is called boiling. Boiling
continues until the entire
liquid becomes a gas.
28
Science Alive for VELS Level 5
Foggy mirrors
Have you noticed how the mirror in the bathroom ‘fogs up’ after a hot shower? The ‘fog’ is actually
formed when water vapour that evaporates from the hot water cools down.
Fog in the air
Some of the energy of the particles
in the water vapour is transferred
away from the vapour to the air.
The transfer of energy leaves the
water vapour with less energy —
so much less energy that
its particles slow down.
The transfer of energy
away from the water
vapour means it cools
down and turns into tiny
droplets of water. These
tiny droplets form
clouds. This process is
called condensation.
Invisible gas
Water vapour forms
when particles in
the hot water gain
enough energy to
escape and become
a gas. You can’t see
water vapour. The
particles in the
water vapour move
around freely. They
have more energy
than the particles
in the liquid water.
Fog on the mirror
The energy from some of
the water vapour is
transferred to the cold
mirror. This results in the
water vapour condensing on the
mirror.
TEAMWORK
7. As a class, make a list of structures and substances
around your home that undergo expansion and
contraction. Divide your list into things that expand
and things that contract.
29
2. Solids, liquids and gases
I CAN:
describe what happens to the
particles in a substance as it
changes state
explain why substances
expand when heated.
Che
THINK
4. The steel rails used in train tracks are placed
end to end in a line to form each side of a train
track. Gaps are left between the steel rails. Why
do you think these gaps are left between the
rails? Use the word ‘expansion’ in your
explanation.
5. What is the relationship between the amount of
energy the particles in a substance have and the
state (phase) of the substance?
6. Explain why many substances contract when they
are cooled.
✓ learning
REMEMBER
1. What happens to the movement of particles as
a substance changes from a solid to a liquid?
2. What happens to the movement of particles as
a substance changes from a gas to a liquid?
3. Why do substances often expand when they are
heated?
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