NCERT Class 9 Science Chapter 1 – Matter in Our Surroundings

NCERT Class 9 Science Chapter 1 introduces the fundamental concept of matter and explains how particles behave in different physical states. NCERT Class 9 Science Chapter 1 builds the scientific foundation for understanding atomic structure, thermodynamics, and physical chemistry in higher classes.

NCERT Class 9 Science Chapter 1 explains that matter is anything that has mass and occupies space. It discusses particle nature of matter, diffusion, force of attraction, and the three physical states — solid, liquid and gas.

The chapter also introduces important scientific concepts such as Kelvin scale (0°C = 273 K), melting point, boiling point (373 K), latent heat of fusion, latent heat of vaporisation, sublimation, and evaporation, which are foundational for Class 10 Science and competitive examinations like NEET and JEE.

NCERT Class 9 Science Chapter 1 develops conceptual clarity about interconversion of states of matter through changes in temperature and pressure, making it one of the most important introductory chapters in Physics and Chemistry.

For structured preparation of NCERT Class 9–12 for UPSC, BPSC and State PCS examinations, strengthen your basics with our complete NCERT Book Notes PDF for Class 9-12, available inside the NCERT foundation course level-2.

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1. Introduction

• Everything around us including air, water, soil, food, plants, animals, clouds, stars and even microscopic organisms is made up of matter.
• Matter is defined as anything that occupies space and has mass.
• The SI unit of mass is kilogram (kg) and the SI unit of volume is cubic metre (m³).
• 1 litre (L) = 1 cubic decimetre (1 dm³), 1 mL = 1 cm³, and 1 L = 1000 mL.
• Ancient Indian philosophers classified matter into Panch Tatva – Air, Earth, Fire, Sky and Water.
• Modern science classifies matter based on physical properties and chemical nature.
• In this chapter, matter is studied only on the basis of its physical properties.

2. Physical nature of matter

• Matter is not continuous but made up of tiny particles.
• When salt or sugar dissolves in water, water level does not increase significantly because particles occupy spaces between water particles.
• Potassium permanganate experiment shows that one crystal can colour about 1000 L of water, proving particles are extremely small.
• Even after repeated dilution, colour remains visible, showing particles keep dividing into smaller particles.
• This confirms that particles of matter are very small beyond imagination.

3. Characteristics of particles of matter

3.1 Particles of matter have space between them

• Dissolving salt, sugar, Dettol, or potassium permanganate in water proves there are spaces between particles.
• Tea, coffee and lemonade formation also demonstrate intermixing due to spaces.
• The particles of one substance occupy the inter-particle spaces of another.
• This property allows substances to form homogeneous mixtures.

3.2 Particles of matter are continuously moving

• Smell of incense stick spreads throughout a room without stirring, proving movement of particles.
• Ink dropped in water spreads gradually due to diffusion.
• Diffusion is defined as intermixing of particles of two substances on their own.
• Diffusion is faster in gases, slower in liquids, and slowest in solids.
• Increase in temperature increases kinetic energy, which increases rate of diffusion.

3.3 Particles of matter attract each other

• Force of attraction exists between particles and keeps them together.
• Human chain activity demonstrates varying strength of attraction.
• Attraction is strongest in solids, weaker in liids, and weakest in gases.
• Greater force of attraction results in rigidity.

4. States of matter

• Matter exists in three states – solid, liquid and gas.
• States differ due to variation in inter-particle distance, force of attraction and kinetic energy.
• Fig. 1.5 in the textbook shows magnified schematic diagrams of particle arrangement.

5. The solid state

• Solids have definite shape, definite volume and distinct boundaries.
• They are rigid and incompressible due to very small inter-particle space.
• Particles vibrate about fixed positions.
• Solids have maximum force of attraction.
• Examples include iron nail, chalk, wooden stick.
• Sponge is compressible because it has air trapped in pores, not because particles are far apart.

6. The liquid state

• Liquids have fixed volume but no fixed shape.
• They take the shape of the container.
• Liquids are fluid and can flow.
• Inter-particle space is greater than solids but less than gases.
• Force of attraction is intermediate.
• Liquids show diffusion faster than solids.
• Aquatic animals survive due to dissolved oxygen in water.

7. The gaseous state

• Gases have no fixed shape and no fixed volume.
• They fill the entire container.
• Gases are highly compressible.
• LPG (Liquefied Petroleum Gas) and CNG (Compressed Natural Gas) are stored under pressure.
• Inter-particle space is maximum and force of attraction is minimum.
• Gas particles move randomly at high speed.
• Gas pressure is due to force exerted per unit area by particles on container walls.

8. Effect of temperature on states of matter

• Increase in temperature increases kinetic energy of particles.
• Melting point is the temperature at which a solid changes into liquid at atmospheric pressure.
• Melting point of ice is 273.15 K (0°C).
• 0°C = 273 K, and Kelvin is SI unit of temperature.
• Latent heat of fusion is the heat required to convert 1 kg solid to liquid at melting point.
• Boiling point of water is 373 K (100°C).
• Latent heat of vaporisation is the heat required to convert 1 kg liquid to gas at boiling point.
• During change of state, temperature remains constant because heat is used to overcome attraction forces.

9. Effect of pressure on states of matter

• Applying pressure reduces inter-particle distance.
• Gases can be liquefied by increasing pressure and decreasing temperature.
• Solid carbon dioxide (dry ice) sublimates directly at 1 atmosphere pressure.
• 1 atmosphere = 1.01 × 10⁵ Pascal (Pa).
• Atmospheric pressure at sea level is 1 atm.

10. Sublimation and deposition

• Sublimation is direct conversion of solid to gas without liquid stage.
• Deposition is direct conversion of gas to solid.
• Examples include camphor, naphthalene, ammonium chloride, dry ice.

11. Evaporation

• Evaporation is conversion of liquid to vapour at any temperature below boiling point.
• It is a surface phenomenon.
• Particles with higher kinetic energy escape from surface.
• Evaporation causes cooling because energy is absorbed from surroundings.

12. Factors affecting evaporation

• Increase in surface area increases evaporation.
• Increase in temperature increases evaporation.
• Decrease in humidity increases evaporation.
• Increase in wind speed increases evaporation.
• Cotton clothes absorb sweat and promote evaporation, causing cooling.

13. Explanation of cooling effects

• Acetone or petrol evaporates quickly and absorbs heat from skin, causing cooling.
• Desert cooler works better on hot dry days due to low humidity.
• Water in earthen pot cools due to evaporation through pores.
• Water droplets form on cold glass due to condensation of water vapour.

14. Interconversion of states of matter

• Solid → Liquid → Gas occurs by increasing temperature.
• Gas → Liquid → Solid occurs by decreasing temperature or increasing pressure.
• The process is reversible under suitable conditions.
• Interconversion depends on temperature and pressure.

15. Conclusion

• Matter is made of tiny particles.
• Particles have space, motion and attraction.
• States of matter depend on inter-particle force and kinetic energy.
• Change of state involves latent heat without temperature change.
• Evaporation causes cooling and depends on environmental factors.

16. Exam oriented facts

• Matter – Anything that has mass and occupies space.
• Diffusion – Intermixing of particles due to random motion.
• Melting point – Temperature at which solid converts to liquid at atmospheric pressure.
• Boiling point – Temperature at which liquid converts to gas at atmospheric pressure.
• Latent heat of fusion – Heat required to convert 1 kg solid to liquid at melting point without temperature change.
• Latent heat of vaporisation – Heat required to convert 1 kg liquid to gas at boiling point without temperature change.
• Sublimation – Direct conversion of solid to gas.
• Evaporation – Surface phenomenon occurring below boiling point causing cooling.
• Atmospheric pressure – Pressure exerted by air, equal to 1.01 × 10⁵ Pa at sea level.
• Kelvin scale – SI temperature scale where 0°C = 273 K.

Understanding NCERT Class 9 Science Chapter 1 is essential to develop scientific reasoning about how matter behaves under different physical conditions.

This chapter builds the foundation for temperature scales, phase changes, diffusion and particle theory, which are directly applied in Class 10 Science and advanced Physics and Chemistry.

For school exams, students must focus on melting point (273 K), boiling point (373 K), latent heat concepts, Kelvin conversion and factors affecting evaporation.

For NEET and JEE foundation preparation, NCERT Class 9 Science Chapter 1 provides conceptual clarity about molecular motion, energy changes and state transitions.

Continue reading NCERT Class 9 Science Chapter 2 – Is Matter Around Us Pure? to understand mixtures, solutions, colloids and chemical combinations.

FAQs

Q1. What is NCERT Class 9 Science Chapter 1 about?
It explains the particle nature of matter, three states of matter (solid, liquid and gas), diffusion, evaporation, latent heat and interconversion of states through changes in temperature and pressure.

Q2. What are the three states of matter discussed in NCERT Class 9 Science Chapter 1?
The three states of matter are solid, liquid and gas, which differ in intermolecular force, particle movement and compressibility.

Q3. What is the Kelvin scale conversion in Chapter 1?
The Kelvin scale is the SI unit of temperature and the conversion formula is K = °C + 273, which means 0°C equals 273 K.

Q4. What is latent heat in NCERT Class 9 Science Chapter 1?
Latent heat is the heat absorbed or released during a change of state without any change in temperature, such as melting at 273 K or boiling at 373 K.

Q5. Why is NCERT Class 9 Science Chapter 1 important for competitive exams?
It builds conceptual clarity about particle theory, temperature scales, energy changes and phase transitions, which are essential foundations for NEET and JEE preparation.

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