Matter
1. What is Matter?
Anything that has MASS and OCCUPIES space (volume) is called matter.
'Everything around us — the air we breathe, the water we drink, the food we eat, the clothes we wear — is made of MATTER.'
2. Physical Nature of Matter
| Property | Explanation |
|---|---|
| Matter is made up of PARTICLES | Tiny, invisible particles (atoms/molecules) |
| Particles are in CONTINUOUS motion | Kinetic energy keeps them moving |
| Particles have SPACES between them | Intermolecular spaces |
| Particles ATTRACT each other | Intermolecular forces of attraction |
3. Kinetic Theory of Matter
The kinetic theory explains the behaviour of matter based on the MOTION of particles.
Postulates:
- All matter is composed of TINY particles.
- Particles are in CONSTANT random motion.
- Particles have KINETIC energy that INCREASES with temperature.
- There are INTERMOLECULAR spaces between particles.
- Intermolecular FORCES hold particles together.
4. Three States of Matter
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | DEFINITE | Takes container SHAPE | Fills container |
| Volume | DEFINITE | DEFINITE | NO definite volume |
| Compressibility | Negligible | Slight | HIGH |
| Intermolecular forces | STRONGEST | WEAKER | WEAKEST |
| Intermolecular spaces | VERY SMALL | SMALL | LARGE |
| Particle arrangement | REGULAR pattern | IRREGULAR | RANDOM |
5. Interconversion of States
Melting: Solid → Liquid (heat ABSORBED) Freezing: Liquid → Solid (heat RELEASED) Vaporisation: Liquid → Gas (heat ABSORBED) Condensation: Gas → Liquid (heat RELEASED) Sublimation: Solid → Gas DIRECTLY (heat ABSORBED) Deposition: Gas → Solid DIRECTLY (heat RELEASED)
6. Sublimation
The DIRECT change of a SOLID into a GAS (vapour) on heating, WITHOUT passing through the LIQUID state.
Examples of substances that sublimate:
- Camphor (kapur)
- Ammonium chloride (NH₄Cl)
- Iodine (I₂)
- Naphthalene (mothballs)
- Dry ice (solid CO₂)
'When camphor is heated, it turns DIRECTLY into vapour without melting. The vapour then DEPOSITS on a cool surface as solid camphor again.'
7. Deposition
The DIRECT change of GAS into SOLID without passing through the LIQUID state.
Example: Frost formation — water vapour in air changes DIRECTLY to ice crystals on cold surfaces.
8. Diffusion
The SPONTANEOUS mixing of particles of TWO substances due to their random motion.
Examples:
- Smell of perfume SPREADS across a room
- Potassium permanganate crystals DISSOLVE and colour water PURPLE
- Tea leaves BREW in hot water
Factors affecting diffusion:
| Factor | Effect |
|---|---|
| Temperature | HIGHER temperature → FASTER diffusion |
| Density of medium | LOWER density → FASTER diffusion |
| Size of particles | SMALLER particles → FASTER diffusion |
Worked Example: Why does sugar dissolve faster in HOT water than in cold water?
At HIGHER temperature, water molecules have MORE kinetic energy and move FASTER. This increases the rate of diffusion of sugar particles.
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| 'Gas has a definite volume' | Gas EXPANDS to fill its container — it has NO definite volume or shape |
| 'Sublimation is solid to liquid' | Sublimation is SOLID to GAS DIRECTLY. Melting is SOLID to LIQUID |
| 'All solids sublime' | Only SOME solids (camphor, iodine, ammonium chloride) sublime. MOST solids melt first |
| 'Diffusion happens only in gases' | Diffusion happens in ALL states — gases (fastest), liquids (slower), solids (very slow) |
ICSE Exam Focus (5–6 marks)
- 2-mark questions: Define matter, states of matter
- 3-mark questions: Differences between states (any two)
- 4-mark questions: Explain sublimation with examples
- 5-mark questions: Kinetic theory and diffusion related questions
Self-Test
Q1. Define matter. Give two examples. A1. Matter is anything that has MASS and occupies SPACE (volume). Examples: Water, air, wood, iron.
Q2. Name the process: Solid changing directly into gas on heating. A2. SUBLIMATION. Example: Camphor, iodine, ammonium chloride.
Q3. Why does a gas fill its container completely? A3. Gas particles have VERY WEAK intermolecular forces and LARGE intermolecular spaces. They move FREELY and randomly in all directions, filling the entire container.
Q4. List three factors that affect the rate of diffusion. A4. (1) Temperature — higher temperature increases rate. (2) Density of medium — lower density increases rate. (3) Size of particles — smaller particles diffuse faster.
Q5. What is the difference between evaporation and boiling? A5. Evaporation occurs at the SURFACE at ANY temperature; boiling occurs THROUGHOUT the liquid at a FIXED boiling point. Evaporation is slower and causes cooling.
Q6. Arrange solids, liquids, and gases in order of increasing intermolecular forces. A6. Gases (weakest) → Liquids → Solids (strongest).
