Everything around you is made of matter.
The desk, the water in a bottle, the air in a room and even your own body contain matter.
Matter can appear in different states.
The three states we meet most often in everyday life are solid, liquid and gas.
Understanding these states helps explain why ice keeps its shape, why water flows and why air spreads through a room.
What is matter?
Matter is anything that has mass and occupies space.
This means matter has some amount of material in it and takes up room.
Some matter is easy to see.
Examples include:
- a book
- a stone
- a glass of water
- a wooden table
- a metal spoon
Other matter may be harder to notice.
Air is a good example.
You usually cannot see the air around you, but air still has mass and occupies space.
How can we tell that air occupies space?
Think about blowing up a balloon.
As air enters the balloon, the balloon becomes larger.
The air inside is taking up space.
This is one simple sign that gases are also matter.
The three common states
Matter on Earth is commonly found as:
- solid
- liquid
- gas
Each state behaves differently because its particles have different arrangements and different freedom to move.
What are particles?
Scientists describe matter as being made of extremely small particles.
Depending on the substance, these may include atoms, molecules or ions.
For this beginner explanation, we can simply call them particles.
The particles are far too small to see individually with our eyes.
A particle model helps us imagine what is happening inside solids, liquids and gases.
Solids
A solid normally has a definite shape and a definite volume.
This means a solid keeps its own shape instead of taking the shape of its container.
Examples include:
- a pencil
- an ice cube
- a coin
- a brick
- a metal key
If you move a key from a table into a box, the key does not become box shaped.
Its shape stays approximately the same.
Solids have a definite volume
A solid also occupies a particular amount of space.
Moving it from one place to another does not normally cause it to expand and fill all available space.
A wooden block placed inside a large container remains a wooden block.
It does not spread through the whole container.
What are particles like in a solid?
In a simple particle model, the particles in a solid are close together.
They are held in positions relative to one another and can vibrate, but they do not move freely through the material in the way particles in a liquid or gas can.
This helps explain why solids resist changing shape.
Not every solid is hard
The word solid does not always mean hard.
A sponge is a solid even though it can be squeezed.
Rubber is a solid even though it can bend.
Many solids can change shape when a force is applied.
The important idea is that a solid normally has its own shape and does not flow to fill its container like a liquid.
Solids can have many structures
Some solids have particles arranged in highly organized repeating patterns.
Other solids have less regular arrangements.
At this level, you do not need to memorize these structures.
The main point is that solid particles remain closely associated and the material keeps a definite form.
Liquids
A liquid has a definite volume but does not have a fixed shape of its own.
Instead, it flows and takes the shape of the part of the container it occupies.
Examples include:
- water
- milk
- cooking oil
- juice
A liquid changes shape when the container changes
Imagine pouring water from a tall glass into a wide bowl.
The water changes shape.
It spreads across the bottom of the bowl.
But if no water is lost, the amount of water remains the same.
The liquid changes shape without automatically changing its total volume.
Liquids can flow
Liquids move past one another internally, which allows the material to flow.
If you tilt a cup of water, gravity causes the water to move.
A solid object such as a wooden cube does not flow in the same way.
What are particles like in a liquid?
Liquid particles are still close together, but they can move around one another more freely than particles in a solid.
This helps explain two important properties:
- liquids can flow
- liquids can change shape to match their container
The particles are not normally as widely separated as the particles in a gas.
Liquids do not fill every part of a container
Suppose you pour a small amount of water into a large bottle.
The water settles in the lower part of the bottle.
It does not automatically spread evenly through all the empty space above it.
This is different from the behaviour of a gas.
Gases
A gas has neither a fixed shape nor a fixed volume of its own.
A gas spreads out to fill the available space in its container.
Examples include:
- oxygen
- nitrogen
- carbon dioxide
- water vapour
Air is a mixture of gases.
A gas takes the shape of its container
Imagine air inside a balloon.
The air takes the shape of the balloon.
If air is inside a different shaped container, it spreads through that available space instead.
A gas can expand
Gas particles can spread farther apart than particles in solids and liquids.
This means gases can expand to fill available space.
It also means gases can often be compressed more easily than solids or liquids.
What are particles like in a gas?
In the particle model, gas particles are much farther apart on average than particles in solids and liquids.
They move freely in many directions and collide with one another and with the walls of their container.
This movement helps explain why a gas spreads throughout its container.
Gas does not mean nothing
An empty looking container can still contain gas.
A glass sitting on a table may look empty, but it contains air.
The air occupies space even though it is difficult to see.
Compare the three common states
Property Solid Liquid Gas Definite shape Yes No No Definite volume under ordinary conditions Yes Yes No Can flow easily Usually no Yes Yes Fills entire container No No Yes Particle spacing Very close Close Much farther apart on averageShape and volume are different ideas
It is important not to confuse shape with volume.
A liquid changes shape when moved to a differently shaped container.
However, its amount does not automatically change.
A gas changes both shape and occupied volume because it expands through the available space.
Example: Water in three states
Water is useful because we commonly experience it in more than one state.
Solid water:
Ice.
Liquid water:
The water you drink.
Gaseous water:
Water vapour.
The substance is still water even though its physical state is different.
Water vapour is invisible
This is an important detail.
Water vapour itself is an invisible gas.
The white cloud you may see above hot water is mostly tiny liquid water droplets that formed when water vapour cooled and condensed.
So the visible mist is not the same thing as invisible water vapour.
A substance can change state
Matter can move from one state to another when conditions change.
For example, heating or cooling can cause changes of state.
Common changes include:
- melting
- freezing
- evaporation
- boiling
- condensation
You will explore these changes in more detail in the related lesson.
Melting
Melting is a change from solid to liquid.
An ice cube can melt into liquid water when it receives enough thermal energy from its surroundings.
Freezing
Freezing is a change from liquid to solid.
Liquid water can freeze into ice when enough thermal energy is transferred away under suitable conditions.
Evaporation
Evaporation is a change in which particles escape from the surface of a liquid and enter the gas state.
Evaporation can happen below the boiling temperature.
This is one reason wet clothes can dry without the water boiling.
Boiling
Boiling is vaporization that occurs throughout a liquid when the conditions are suitable.
Bubbles of vapour form within the liquid.
Boiling and evaporation both involve liquid changing into gas, but they do not happen in exactly the same way.
Condensation
Condensation is a change from gas to liquid.
You may notice droplets forming on the outside of a cold glass.
Water vapour in the surrounding air can cool near the glass and condense into liquid droplets.
Does matter disappear during a state change?
When ice melts, the water has not vanished.
It has changed physical state.
Likewise, when liquid water evaporates, the water particles move into the gas state rather than becoming nothing.
In a closed system, matter is conserved even though its physical form may change.
Common mistake 1: Thinking gases have no mass
Gases are matter.
They have mass and occupy space.
A gas may simply be less obvious because many gases are colourless and transparent.
Common mistake 2: Thinking liquids have no volume
A liquid does have volume.
What it lacks is a fixed shape of its own.
If you pour the same amount of water into a new container, the shape changes but the amount does not automatically change.
Common mistake 3: Thinking every gas is air
Air is a mixture containing several gases.
Other gases can exist separately.
For example, carbon dioxide and oxygen are individual substances that can exist as gases under ordinary conditions.
Common mistake 4: Thinking steam and water vapour always mean the visible cloud
Invisible water vapour is the gaseous form of water.
The visible cloud near a kettle contains tiny liquid droplets formed by condensation.
Common mistake 5: Thinking particles become bigger when matter expands
When a gas expands, the particles themselves do not need to become larger.
Instead, the average distance between the particles can increase.
The particle model separates the size of particles from the space between particles.
Practice 1
A wooden block is moved from a table into a bucket.
Does it take the shape of the bucket?
No.
It remains a solid with its own shape.
Practice 2
Juice is poured from a bottle into a glass.
What changes?
The shape of the juice changes to match the part of the glass it occupies.
If none is spilled, its amount remains the same.
Practice 3
Air is pumped into a bicycle tyre.
Why is air considered matter?
Air has mass and occupies space inside the tyre.
Practice 4
Which state normally fills all available space inside a closed container?
Gas.
Practice 5
Which state normally has a definite volume but takes the shape of its container?
Liquid.
Practice 6
Which state normally has both a definite shape and a definite volume?
Solid.
Practice 7
An ice cube becomes liquid water.
What change of state occurred?
Melting.
Practice 8
Water droplets appear on the outside of a cold bottle.
Which change of state is involved?
Condensation of water vapour from the surrounding air into liquid water.
Particle model challenge
Imagine three boxes.
In the first box, particles are very close and remain in positions relative to one another.
In the second box, particles are close together but can move around one another.
In the third box, particles are much farther apart and move freely through the available space.
The boxes represent:
- solid
- liquid
- gas
What about plasma?
Solid, liquid and gas are not the only possible states of matter.
Plasma is another state found in places such as stars and some very high temperature environments.
Plasma contains electrically charged particles and behaves differently from an ordinary gas.
For this article, the focus is on solid, liquid and gas because these are the three states most commonly encountered in everyday conditions on Earth.
The main idea
Matter has mass and occupies space.
The three common states of matter are solid, liquid and gas.
A solid normally has a definite shape and volume.
A liquid normally has a definite volume but takes the shape of its container.
A gas has neither a fixed shape nor a fixed volume and spreads through the available space.
The particle model helps explain these differences by considering how closely particles are arranged and how freely they can move.
Changes in conditions can also move matter from one state to another without changing the fact that it is matter.
Continue learning
The next lesson will investigate how matter changes between solid, liquid and gas states.