CLASS 9 SCIENCE — CHAPTER 1
Matter in Our Surroundings
Exam-Oriented Complete Revision Notes
■ Special Features
• Key concepts in simple language
• Important definitions and comparisons
• Must-remember facts for exams
• Formulae + temperature conversions
• Reason-based questions and quick revision points
1. What is Matter?
Matter is anything that has mass and occupies space.
Examples: air, water, stone, wood, milk, oxygen, etc.
Matter is made up of very small particles.
2. Characteristics of Particles of Matter
(i) Particles have spaces between them: Sugar dissolves in water because sugar particles occupy
spaces between water particles.
(ii) Particles are continuously moving: Their motion increases when temperature increases.
(iii) Particles attract each other: The force of attraction helps hold particles together.
(iv) Particles are very small: A small amount of substance may contain an enormous number of particles.
3. States of Matter
Solid: Fixed shape and fixed volume; particles are closely packed; strongest attraction; least compressible.
Liquid: Fixed volume but no fixed shape; particles can move/slide; flows; slightly compressible.
Gas: Neither fixed shape nor fixed volume; particles are far apart; weak attraction; highly compressible; fills
the container.
4. Interconversion of States
Matter can change from one state to another by changing temperature or pressure.
Melting/Fusion: Solid → Liquid
Freezing/Solidification: Liquid → Solid
Vaporisation: Liquid → Gas
Condensation: Gas → Liquid
Sublimation: Solid → Gas directly (and reverse deposition).
Examples of sublimating substances include camphor and ammonium chloride.
5. Effect of Temperature
On heating, particles gain kinetic energy and move faster. This can overcome intermolecular attraction and
change the state of matter.
Melting point: Temperature at which a solid changes into a liquid at atmospheric pressure. Ice melts at
273.15 K (0°C).
Boiling point: Temperature at which a liquid changes into gas throughout the liquid at atmospheric
Matter in Our Surroundings
Exam-Oriented Complete Revision Notes
■ Special Features
• Key concepts in simple language
• Important definitions and comparisons
• Must-remember facts for exams
• Formulae + temperature conversions
• Reason-based questions and quick revision points
1. What is Matter?
Matter is anything that has mass and occupies space.
Examples: air, water, stone, wood, milk, oxygen, etc.
Matter is made up of very small particles.
2. Characteristics of Particles of Matter
(i) Particles have spaces between them: Sugar dissolves in water because sugar particles occupy
spaces between water particles.
(ii) Particles are continuously moving: Their motion increases when temperature increases.
(iii) Particles attract each other: The force of attraction helps hold particles together.
(iv) Particles are very small: A small amount of substance may contain an enormous number of particles.
3. States of Matter
Solid: Fixed shape and fixed volume; particles are closely packed; strongest attraction; least compressible.
Liquid: Fixed volume but no fixed shape; particles can move/slide; flows; slightly compressible.
Gas: Neither fixed shape nor fixed volume; particles are far apart; weak attraction; highly compressible; fills
the container.
4. Interconversion of States
Matter can change from one state to another by changing temperature or pressure.
Melting/Fusion: Solid → Liquid
Freezing/Solidification: Liquid → Solid
Vaporisation: Liquid → Gas
Condensation: Gas → Liquid
Sublimation: Solid → Gas directly (and reverse deposition).
Examples of sublimating substances include camphor and ammonium chloride.
5. Effect of Temperature
On heating, particles gain kinetic energy and move faster. This can overcome intermolecular attraction and
change the state of matter.
Melting point: Temperature at which a solid changes into a liquid at atmospheric pressure. Ice melts at
273.15 K (0°C).
Boiling point: Temperature at which a liquid changes into gas throughout the liquid at atmospheric
