Matter

1. What is Matter?

Anything that occupies space and has mass is called matter.

The air we breathe, the water we drink, the food we eat, the books we read — all are matter.

Examples: Wood, water, air, iron, plastic, cloth.
Non-examples: Light, heat, sound, thoughts (they do not have mass or occupy space).

2. States of Matter

Matter exists in three main states: solid, liquid, and gas.

Comparison Table: Three States of Matter

Common Mistake: Saying 'liquids have no fixed volume.' Liquids do have a fixed volume — 1 litre of water remains 1 litre whether in a bottle or a bucket. They have no fixed SHAPE, but they do have fixed volume.

3. Properties of Solids

• Solids have a definite shape and volume.
• The particles are very closely packed.
• The intermolecular force of attraction is very strong.
• Solids cannot be compressed easily.
• Examples: Stone, wood, iron, ice.

Worked Example: Why does a wooden block keep its shape even when you push it?

In a solid, the particles are tightly packed in a fixed position. They can only vibrate about their mean positions. This gives the solid its definite shape.

4. Properties of Liquids

• Liquids have a definite volume but no definite shape.
• The particles are less closely packed than in solids.
• The intermolecular force is weaker than in solids.
• Liquids can flow (fluidity).
• Examples: Water, milk, oil, juice.

Worked Example: Why does water take the shape of a container but its volume stays the same?

The molecules in a liquid can slide past each other, allowing it to take the container's shape. However, the intermolecular forces keep them close enough that the volume does not change.

5. Properties of Gases

• Gases have no definite shape or volume.
• The particles are very far apart.
• The intermolecular force is very weak.
• Gases are highly compressible.
• Examples: Oxygen, nitrogen, carbon dioxide, hydrogen.

Exam Focus (2 marks): 'Why is the smell of perfume felt from a distance?'

Perfume molecules evaporate and move rapidly through the air (diffusion). This is possible because gas molecules are far apart with weak forces, allowing them to spread easily.

6. Molecular Arrangement

Solids — Crystalline and Amorphous

• Crystalline solids: Particles arranged in a regular, repeating pattern (e.g., diamond, salt, sugar).
• Amorphous solids: Particles arranged randomly (e.g., glass, rubber, plastic).

How Heating Affects States

Solid -> (heating) -> Liquid -> (heating) -> Gas

Melting: Solid to liquid (melting point).
Boiling: Liquid to gas (boiling point).
Condensation: Gas to liquid.
Freezing: Liquid to solid.

7. Diffusion

Diffusion is the process by which particles of one substance mix with particles of another substance due to their random motion.

Examples:

• Spreading of ink in water.
• Smell of food spreading in a room.
• Oxygen diffusing into blood in lungs.

Rate of diffusion is fastest in gases, slower in liquids, and extremely slow in solids.

Common Mistake: Thinking diffusion only happens in gases. Diffusion occurs in all three states but at different rates.

8. Self-Test

1. Define matter with two examples.
2. List three properties of solids.
3. Why can a gas be compressed easily but a solid cannot?
4. What is diffusion? Give one example from daily life.
5. Explain why liquids have a definite volume but no definite shape.
6. What happens to the arrangement of molecules when ice melts into water?
7. Name the process: (a) Solid to liquid (b) Gas to liquid (c) Liquid to gas.

9. Answers to Self-Test

1. Anything that occupies space and has mass. Examples: water, wood, air.
2. Definite shape, definite volume, cannot be compressed easily.
3. In gases, molecules are far apart with large empty spaces, so they can be pushed closer. In solids, molecules are tightly packed with no empty space.
4. The mixing of particles of one substance with another. Example: aroma of cooking food spreading through the house.
5. Molecules can slide past each other (so shape changes) but remain close enough that volume stays constant.
6. In ice, molecules are in a fixed, regular pattern. On melting, they gain energy and start sliding past each other, losing the fixed pattern.
7. (a) Melting (b) Condensation (c) Boiling or evaporation.