22

Science Alive for VELS Level 5

States of matterverything 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.

The three main states of matter are solid, liquid and gas.

E

Solids do not usually flowMost solids are too rigid to flow.

Substances such as sugar, which

are made up of many small solid

pieces, can be poured.

Gases flowLike 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 compressedGases 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.

Gases change shapeGases 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 changesGases expand to fill the

containers they are placed

in. Gases do not have a

fixed volume.

Solids have a constant shapeSolids 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.

 

232. Solids, liquids and gases

Liquids change shapeA 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.

Liquids have a fixed volumeThe 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.

Liquids flowLiquids can be

poured from

one container

to another.

When the

container is

full, it

overflows.

Solids have a fixed volumeIf you move a solid from container

to container, the amount of space it

takes up (volume) is the same.

Investigating solids, liquids and gases

You will need:

a piece of dowel large plastic syringewater plasticine salt sponge.

• Copy the following table.

• 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?

Property Solid (dowel) Liquid (water) Gas (air)

Fixed shape

Fixed volume

Able to be compressed

REMEMBER1. 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?

THINK3. Classify each of the following

items as a solid, liquid or gas.Oxygen Talcum powder Glass Vaseline Oil HoneyWood Sand

4. Why is a bicycle frame made of solids?

5. Why are bicycle tyres filled with air?

OBSERVE6. 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.

✓ lea

rnin

g I CAN:name the three states of matterdescribe the properties of the three states of matterclassify materials as solids, liquids or gases.

 

26

Science Alive for VELS Level 5

The particle modelll 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 behavedifferently 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 liquidThe 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.

Particles in a solidSolids 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 gasThe 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.

 

272. Solids, liquids and gases

DiffusionDiffusion 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.

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. Air deodoriser

Crystal

Water

Beaker

Hold

straw

Investigating diffusion

You will need:

500 mL beaker

water

straw

potassium permanganate crystals

fragrant spray

protective mat

safety glasses.

• Using the straw as a

guide, put a crystal of

potassium permanganate

in the bottom of a beaker of

water. Remove the straw

and record your

observations.

1. Draw a diagram of the

movement of the potassium

permanganate through the

water.

• Release some of the fragrant spray in one corner of

the classroom. Move away and observe by smell.

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?

✓ lea

rnin

g 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.

REMEMBER

1. What is the basis of the particle model?

2. What is diffusion?

3. Give an everyday example of diffusion at

work.

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

liquids slowly mix together even though

you don’t stir them. Explain how this

happens.

Property Solid Liquid Gas

Particle arrangement

Force of attraction between

particles

Movement of particles

Ability to diffuse

 28

Science Alive for VELS Level 5

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 stateA 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.

MeltingAs 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.

LiquidAs a liquid is

heated, its

particles move

and roll over

each other

faster and

faster. The

liquid begins

to expand.

BoilingIf 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.

GasAs 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.

 

292. Solids, liquids and gases

Foggy mirrorsHave 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.

Invisible gasWater 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 in the airSome 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.

Fog on the mirrorThe energy from some of

the water vapour is

transferred to the cold

mirror. This results in the

water vapour condensing on the

mirror.

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?

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.

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.

Chec

kpoint

✓ le

arn

ing I CAN:

describe what happens to the particles in a substance as it changes stateexplain why substances expand when heated.