Everything around us is made of tiny particles. How tightly those particles are packed and how they move decides whether something is a solid, a liquid or a gas.
Ages
7–14 (rough guide)
Level
Foundation
Subject
Science
Time
20 minutes
Format
Online + printable
Stage
UK Year 4 science and KS3 · roughly US Grades 2–5 physical science
None. Having seen ice melt and a kettle steam helps.
Learn it
How it works
Solids keep their shape. Particles are packed tightly in rows and only vibrate on the spot. Examples: ice, wood, a coin.
Liquids flow and take the shape of their container but keep the same volume. Particles are close but can slide past each other. Examples: water, milk, oil.
Gases spread out to fill any space. Particles are far apart and move quickly in all directions. Examples: steam, oxygen, the gas in a balloon.
Changes of state: melting (solid → liquid), freezing (liquid → solid), evaporating or boiling (liquid → gas), condensing (gas → liquid). Water melts at 0 °C and boils at 100 °C at sea level.
Heating gives particles more energy so they move more; cooling does the opposite.
Worked example 1
Why do drops of water appear on a cold can taken from the fridge?
Air contains water vapour (a gas).
The cold can cools the air touching it.
Cooled water vapour changes from gas to liquid.
Answer: Water vapour in the air condenses on the cold surface.
Try it online · print it · check it
Practice questions
Foundation · ages 7–14
States of matter
NameDate
Answer each question in one or two words.
1.Is honey a solid, liquid or gas?
2.What is the change from liquid to gas called?
3.What is the change from liquid to solid called?
4.At what temperature (°C) does pure water freeze?
5.In which state are particles furthest apart?
6.Puddles disappear on a sunny day. What process is this?
7.Chocolate goes runny in your hand. What change of state is this?
Foundation · answersAnswer key
States of matter — answer key
Answer each question in one or two words.
1.Is honey a solid, liquid or gas?liquid
2.What is the change from liquid to gas called?evaporation
3.What is the change from liquid to solid called?freezing
4.At what temperature (°C) does pure water freeze?0
5.In which state are particles furthest apart?gas
6.Puddles disappear on a sunny day. What process is this?evaporation
7.Chocolate goes runny in your hand. What change of state is this?melting
Tips
Common mistakes
Saying steam you can see is a gas — the white cloud is tiny liquid droplets; true water vapour is invisible.
Thinking sand is a liquid because it pours. Each grain is a solid.
