Std . 9 , CBSE
✅ 1. What is Matter?
- Anything that has mass and occupies space is called matter.
- Examples: air, water, stone, wood, metals, food, etc.
✅ 2. Classification of Matter
A. Based on Physical State
- Solid
- Fixed shape and volume
- Particles closely packed
- Very little space between particles
- Cannot be compressed
- Liquid
- No fixed shape, but fixed volume
- Takes shape of container
- Particles have more space than solids
- Can be slightly compressed
- Gas
- No fixed shape or volume
- Particles are far apart
- Highly compressible
- Fill entire container
B. Based on Purity
- Pure Substances
- Made of one kind of particles
- Elements or Compounds
- Mixtures
- Made of more than one kind of particles
- Homogeneous mixture: uniform (e.g., sugar in water)
- Heterogeneous mixture: non-uniform (e.g., sand in water)
✅ 3. Properties of Matter
A. Physical Properties
- State, color, hardness, melting point, boiling point, density, solubility
B. Chemical Properties
- How a substance reacts with other substances
(e.g., iron reacts with oxygen and water to form rust)
✅ 4. Particle Nature of Matter
- Matter is made up of very small particles.
- Evidence:
- Diffusion
- Gases mix with each other automatically
- Example: smell of perfume spreading
- Dissolving
- Salt disappears in water → particles occupy space
- Diffusion
✅ 5. Characteristics of Particles of Matter
- They have space between them.
- They are constantly moving.
- They attract each other.
✅ 6. Change of State
Matter can change state when heat is added or removed.
- Solid → Liquid (melting)
- Liquid → Gas (vaporisation)
- Gas → Liquid (condensation)
- Liquid → Solid (freezing)
Melting point: Temperature at which solid changes to liquid
Boiling point: Temperature at which liquid changes to gas
Example:
- Ice melts to water at 0°C
- Water boils to steam at 100°C
✅ 7. Latent Heat
Heat required to change state without changing temperature.
- Latent heat of fusion: solid → liquid
- Latent heat of vaporisation: liquid → gas
✅ 8. Evaporation
Liquid changes to vapour below boiling point.
Factors affecting evaporation:
- Surface area
- Temperature
- Humidity (less evaporation in humid air)
- Wind speed
Reason for cooling during evaporation:
- Liquid takes heat from surroundings to change into vapour
- Example: sweating cools our body
✅ 9. Sublimation
Solid → Gas directly
Examples: camphor, dry ice (solid CO2), naphthalene
✅ 10. Condensation and Freezing
- Gas → Liquid: condensation
- Liquid → Solid: freezing
Examples: water droplets on cold glass, formation of ice
✅ 11. Mixtures vs Pure Substances
Pure substance
- Same composition throughout
- Example: distilled water, pure copper, sugar
Mixture
- Contains more than one substance
- Can be separated by physical methods:
- filtration
- evaporation
- distillation
- sieving
- chromatography
✅ Key Points to Remember
- Matter has mass and volume
- Particles are very small, have space, move, and attract each other
- Increasing heat increases movement of particles
- States of matter depend on inter-particle space and attraction
- Evaporation causes cooling