CBSE Class 9 Science Notes Chapter 1: Matter in Our Surroundings

Many Class 9 students face challenges when they try to understand matter. The process begins when people notice basic things, such as food scents moving from one room to another and ice cubes turning into water. Chemistry explains these phenomena, but the tiny particles that continually move throughout the process remain difficult to visualize. Students often find it difficult to recall definitions, states of matter, and how temperature or pressure affects these changes. Exam preparation can feel overwhelming.

These CBSE Class 9 Science chapter 1 notes make things simpler. They explain solids, liquids, and gases, along with processes such as evaporation, condensation, sublimation, and deposition. Using real-life examples helps learners connect concepts to everyday experiences. These notes go beyond rote learning, making revision faster and building a strong foundation in science.

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What is Matter?

Everything around us, from water to clouds to stars, is made of matter.

Definition: Matter is anything that has mass and occupies space.

Examples: Water, air, stones, clouds, stars, plants, even a single drop of water.

Physical Nature of Matter

Matter is not a solid block. It consists of extremely tiny particles invisible even under a microscope. These particles are always moving and exert forces of attraction on each other.

Characteristics of Particles

1. Spaces Between Particles: Salt dissolves in water without significantly raising the water level because it fills the spaces between water particles.

2. Continuous Motion: Particles keep moving. Their kinetic energy rises with temperature.

3. Attraction: Particles attract each other. This force is strongest in solids, weaker in liquids, and weakest in gases.

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The Three States of Matter

Matter exists in three states depending on particle arrangement and energy:

Can Matter Change Its State?

Yes. Matter changes its state when temperature or pressure is altered.

Temperature Effects

• Melting (Fusion): Solid → Liquid. Energy used to break particle attractions without raising temperature is Latent Heat of Fusion.

• Boiling (Vaporization): Liquid → Gas. Energy required to convert 1 kg of liquid to gas is Latent Heat of Vaporization.

Special Conversions:

• Sublimation: Solid → Gas (e.g., camphor, naphthalene)

• Deposition: Gas → Solid

Pressure Effects

Increasing pressure compresses particles. CO₂ gas, for example, can turn into dry ice when high pressure and low temperature are applied.

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Evaporation and Cooling

Evaporation occurs when a liquid changes into vapor below its boiling point.

Factors Affecting Evaporation:

• Surface Area: More area speeds up evaporation (e.g., spreading wet clothes).

• Temperature: Higher heat increases evaporation rate.

• Humidity: Lower humidity boosts evaporation.

• Wind Speed: Faster airflow accelerates evaporation.

Cooling Effect: When a liquid evaporates, it absorbs energy from surroundings, lowering temperature. This is why water in an earthen pot stays cool.

Benefits of Class 9 Science Chapter 1 Notes

These notes have been prepared to make learning and revisions much simpler for the students:

• Clarity and Understanding: The notes explain concepts of matter in a simple and easy-to-grasp way.

• Structured Learning: Organized topic-wise, they help students follow a logical learning path.

• Quick Reference: Ideal for last-minute revision before tests and exams.

• Supplementary Resource: Provide extra examples and insights to complement textbooks.

• Effective Revision: Regular use reinforces learning and improves retention of key concepts. 

Read More: NCERT Solutions Class 9 Science Chapter 1 Matter in Our Surroundings

CBSE Class 9 Science Notes Chapter 1 FAQs 

1. Why does ice float on water even though it’s solid?

Ice expands during freezing, making it less dense than water. That’s why it floats.

2. What is diffusion in class 9 science chapter 1 notes? 

Diffusion is the process of mixing and spreading of substances due to the motion of their particles. Gases exhibit the fastest diffusion, which is why the smell of perfume or hot food spreads rapidly across a room.

3. Why does temperature remain constant during a state change? 

During a state change, the heat energy provided (latent heat) is used to break the forces of attraction between particles rather than increasing the kinetic energy (temperature) of the substance.

4. What is the Kinetic Theory of Matter according to class 9 ch 1 science notes? 

The theory states that all matter consists of tiny particles in constant, random motion. This motion explains properties like diffusion, pressure in gases, and the rigidity of solids.

5. How does pressure affect the states of matter? 

By increasing pressure and decreasing temperature, gases can be converted into liquids or even solids. A common example in class 9 matter in our surroundings notes is the storage of solid CO₂ under high pressure.