Solids, Liquids and Gases

A Today you'll learn

Identify the three states of matter: solid, liquid, and gas
Describe the distinctive properties of shape, volume, and compressibility for each state
Explain changes of state: melting, freezing, evaporation, and condensation

B Let's understand

SolidFixed shape & volume

LiquidFixed volume; flows

GasFills any space

Everything around us that has mass and takes up space is called matter. Matter exists in three primary states: solid, liquid, and gas. Solids (like a book or an ice cube) have a definite shape and a fixed volume because their particles are packed very closely together. Liquids (like water or milk) have a fixed volume but take the shape of whatever container they are poured into, because their particles can slide past each other. Gases (like air, oxygen, and steam) have neither a fixed shape nor a fixed volume; their particles spread out freely to fill all available space. Matter can change state when heated or cooled — ice melts into liquid water, and boiling water turns into water vapour.

C See it step by step

Example 1: Why does water take the shape of a bowl when poured from a glass, but a stone does not?

Water is a liquid: liquid particles can slide past each other, allowing liquids to flow and take the shape of the container.
A stone is a solid: particles in a solid are tightly locked in place in a rigid structure.
Therefore, a stone maintains its fixed shape, while water adapts to the container.

Example 2: What happens to water during melting and freezing?

Melting: When solid ice is heated, it absorbs heat energy and turns into liquid water.
Freezing: When liquid water is cooled below 0°C, it loses heat and solidifies back into ice.

D Your turn

Which of the following has a fixed shape and a fixed volume?

Look back at "Let's understand" above for a clue.

E Ready to practise?

Key idea 1

Matter is anything that has mass and occupies space.

Key idea 2

Solids have a definite shape and fixed volume.

Key idea 3

Liquids have a fixed volume but take the shape of their container.

Key idea 4

Gases have no fixed shape and no fixed volume; they fill all available space.

Key idea 5

Heating causes melting and evaporation; cooling causes condensation and freezing.

Warm up

1. Name the three states of matter and give one example of each.

2. Which state of matter has a fixed volume but no fixed shape?

3. What happens when you heat an ice cube? Name the process.

Practise

4. What is the change of liquid water into water vapour called?

5. Why can air be easily compressed inside a balloon while a wooden block cannot?

6. Classify the following: juice, pencil, steam, chair, oxygen, milk.

Challenge

7. What is condensation? Give one everyday example.

8. True or false: Gases have weight.

Download worksheet (PDF)

Question 1: Name the three states of matter and give one example of each.

Answer: Solids (e.g. ice, book), Liquids (e.g. water, milk), Gases (e.g. air, steam).

Question 2: Which state of matter has a fixed volume but no fixed shape?

Answer: Liquid.

Question 3: What happens when you heat an ice cube? Name the process.

Answer: It melts into liquid water; the process is called melting.

Question 4: What is the change of liquid water into water vapour called?

Answer: Evaporation.

Question 5: Why can air be easily compressed inside a balloon while a wooden block cannot?

Answer: Gas particles have large spaces between them and can be pushed closer, whereas particles in a wooden solid are tightly packed.

Question 6: Classify the following: juice, pencil, steam, chair, oxygen, milk.

Answer: Solids: pencil, chair. Liquids: juice, milk. Gases: steam, oxygen.

Question 7: What is condensation? Give one everyday example.

Answer: Condensation is the process where gas cools and turns into liquid (e.g., water droplets forming on the outside of a cold glass).

Question 8: True or false: Gases have weight.

Answer: True — air and gases have mass and take up space.