States of Matter
Discover the three states of matter -- solid, liquid, and gas -- and how they change from one to another.
The Three States of Matter
Everything around you is made of tiny particles (too small to see). How these particles are arranged and how they move determines whether something is a solid, liquid, or gas.
SOLID
Particles are tightly packed in a fixed pattern. They vibrate but stay in place.
Examples: ice, rock, wood, metal
LIQUID
Particles are close but can slide past each other. They move around freely.
Examples: water, milk, juice, oil
GAS
Particles are far apart and move very fast in all directions.
Examples: air, steam, helium
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed shape | Takes shape of container | No fixed shape, fills all space |
| Volume | Fixed volume | Fixed volume | No fixed volume, expands |
| Particles | Tightly packed, vibrate | Close, slide past each other | Far apart, move fast |
| Can be poured? | No | Yes | No (floats freely) |
Changing States
Matter can change from one state to another when heat is added or removed. These changes are reversible -- you can change them back!
State Changes Diagram
SOLID
e.g. Ice
LIQUID
e.g. Water
GAS
e.g. Steam
Melting
Solid → Liquid. Adding heat makes particles move more and spread apart. Example: ice melting into water.
Freezing
Liquid → Solid. Removing heat makes particles slow down and pack together. Example: water freezing into ice.
Evaporation
Liquid → Gas. Adding heat makes particles move so fast they escape as gas. Example: a puddle drying up.
Condensation
Gas → Liquid. Cooling a gas makes particles slow down and come together. Example: water droplets on a cold glass.
The Water Cycle Connection
The water cycle shows how water changes state naturally on Earth:
Oceans
(liquid)
Clouds
(gas condenses)
Rivers
(liquid)
Key Vocabulary
Particle
A tiny piece of matter, far too small to see with the naked eye.
Matter
Anything that has mass and takes up space. Everything is made of matter.
Melting
When a solid changes into a liquid by heating.
Evaporation
When a liquid changes into a gas by heating.
Freezing
When a liquid changes into a solid by cooling.
Condensation
When a gas changes into a liquid by cooling.
Worked Examples
You take ice cubes out of the freezer and leave them on the bench. What happens and why?
Step 1: The room is warmer than the freezer, so heat is added to the ice.
Step 2: The particles in the ice gain energy and start moving more.
Answer: The ice melts -- it changes from a solid to a liquid. This is because heat energy causes the particles to break free from their fixed positions.
Why do water droplets form on the outside of a cold glass on a hot day?
Step 1: There is water vapour (gas) in the air around the glass.
Step 2: The cold glass cools the water vapour near its surface.
Answer: The water vapour condenses -- it changes from a gas to tiny liquid droplets on the cold surface.
Is honey a solid or a liquid?
Step 1: Does honey have a fixed shape? No -- it takes the shape of its container.
Step 2: Can it be poured? Yes, slowly, but it flows.
Answer: Honey is a liquid, even though it is very thick (viscous). It does not have a fixed shape.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
In which state of matter are particles tightly packed and only vibrate in place?
Question 2
What is the process called when a liquid changes into a gas?
Question 3
Which of these is a gas?
Question 4
Water droplets form on a cold mirror in a steamy bathroom. What process is happening?
Question 5
A liquid takes the shape of its container but has a fixed volume. True or false?
Key Concepts Summary
- ●The three states of matter are solid, liquid, and gas.
- ●Solids have a fixed shape and volume; liquids have a fixed volume but no fixed shape; gases have no fixed shape or volume.
- ●Adding heat causes melting (solid → liquid) and evaporation (liquid → gas).
- ●Removing heat causes condensation (gas → liquid) and freezing (liquid → solid).
- ●The water cycle is a natural example of matter changing states.