CBSE Matter In Our Surroundings Class 9 Pdf PDF – NCERT 2…

The Matter in Our Surroundings Class 9 PDF is the foundational chapter of NCERT Science that introduces students to the physical nature of matter, its states, and the particle theory that governs all substances around us.

Chapter 1 of CBSE Class 9 Science establishes the fundamental concepts that form the basis of both Chemistry and Physics at higher levels. Published by NCERT and aligned with the CBSE syllabus 2026-27, this chapter explains how everything we see, touch, or interact with is composed of tiny particles in constant motion. Whether you are preparing for school examinations, NTSE, or building your foundation for Class 10 boards, understanding matter and its behaviour is absolutely essential.

This comprehensive guide covers every topic from the official NCERT textbook, including detailed explanations of states of matter, kinetic theory, interconversion of states, evaporation, and the factors affecting physical changes. Students can download NCERT Books and Solutions PDF directly from this page for offline study and revision.

Matter in Our Surroundings Class 9 PDF – Chapter Overview

The NCERT Class 9 Science Chapter 1 PDF begins with a simple yet profound question: what is matter? According to ancient Indian philosophers, matter was classified into five basic elements—Panch Tatva—comprising air, earth, fire, sky, and water. Modern science defines matter as anything that occupies space and has mass. This definition encompasses everything from the air we breathe to the water we drink and the ground beneath our feet.

The chapter systematically builds upon this definition by introducing the particle nature of matter. Students learn that all matter is made up of extremely small particles that are invisible to the naked eye. These particles are in constant motion, have spaces between them, and attract each other. The strength of this attraction determines whether a substance exists as solid, liquid, or gas at a given temperature and pressure.

Understanding particle theory is crucial because it explains observable phenomena like dissolving sugar in water, smelling perfume from across a room, and the compressibility of gases. The NCERT PDF provides several activities that students can perform at home to verify these properties experimentally.

Three States of Matter – Solid, Liquid, and Gas

The Matter in Our Surroundings Class 9 PDF dedicates significant content to explaining the three common states of matter that students encounter daily. Each state has distinct characteristics based on particle arrangement, intermolecular forces, and energy content.

Solid State

Solids have a definite shape and definite volume because their particles are tightly packed in fixed positions. The particles can only vibrate about their mean positions but cannot move freely. This strong intermolecular force of attraction gives solids their rigidity. Examples include ice, iron, wood, and crystalline substances like common salt. The kinetic energy of particles in solids is minimum compared to liquids and gases.

Liquid State

Liquids have definite volume but no fixed shape—they take the shape of their container. Liquid particles are less tightly packed than solids, allowing them to flow and slide over each other. The intermolecular forces are weaker than in solids but stronger than in gases. This explains why liquids can be poured, why water fills any vessel it is placed in, and why we can swim through water but not through walls.

Gaseous State

Gases have neither definite shape nor definite volume. Gas particles are far apart with negligible intermolecular forces, moving randomly at high speeds. This explains why gases can be compressed easily, why cooking gas fills the entire kitchen, and why we can smell incense from another room. The kinetic energy of gas particles is highest among the three states.

Students preparing for CBSE examinations should focus on comparative questions that ask about differences between states of matter. The PDF includes detailed diagrams showing particle arrangement in each state, which frequently appear in board exam questions worth 2-3 marks.

Interconversion of States and Latent Heat

One of the most important sections in the Matter in Our Surroundings Class 9 PDF covers how matter changes from one state to another. These changes occur due to variations in temperature or pressure, and understanding them is fundamental to both Chemistry and Physics.

Melting and Fusion

Melting is the process of conversion from solid to liquid state. The temperature at which a solid starts melting is called the melting point. For ice, this temperature is 0°C (273K). The heat energy required to convert unit mass of solid into liquid at its melting point is called latent heat of fusion. For ice, this value is 334 J/g, meaning 334 joules of energy are needed to melt 1 gram of ice without changing its temperature.

Vaporisation and Condensation

Boiling is the rapid vaporisation of liquid at its boiling point. Water boils at 100°C (373K) at atmospheric pressure. The latent heat of vaporisation for water is 2260 J/g—nearly seven times greater than latent heat of fusion. This high value explains why steam burns are more severe than boiling water burns, as steam releases enormous energy when condensing on skin.

Sublimation

Sublimation is the direct conversion of solid to gas without passing through the liquid state. Common examples include camphor, naphthalene balls, dry ice (solid CO₂), and iodine. The NCERT PDF describes an activity where camphor is heated in a china dish covered with an inverted funnel—solid camphor sublimes and re-deposits on the cooler funnel surface.

Students studying for competitive examinations like NTSE should also explore how Biological Classification NCERT PDF connects matter concepts to living organisms, as biological processes depend on state changes of water and other substances.

Evaporation – Factors and Cooling Effect

The NCERT Matter in Our Surroundings Class 9 PDF provides detailed coverage of evaporation, a phenomenon students experience daily but often misunderstand. Unlike boiling, evaporation is a surface phenomenon that occurs at any temperature below the boiling point.

Factors Affecting Rate of Evaporation

The CBSE syllabus 2026-27 requires students to understand four main factors that influence evaporation rate:

1. Surface Area: Larger surface area means more molecules can escape simultaneously. Clothes dry faster when spread out than when crumpled.

2. Temperature: Higher temperature provides more kinetic energy to molecules, increasing evaporation rate. Wet floors dry faster in summer than winter.

3. Humidity: High humidity means air already contains water vapour, reducing its capacity to accept more. Clothes dry slowly on humid days.

4. Wind Speed: Moving air carries away evaporated molecules, maintaining concentration gradient. Clothes dry faster on windy days.

Cooling Effect of Evaporation

When liquid evaporates, the molecules with highest kinetic energy escape first. This leaves behind molecules with lower average energy, reducing the liquid’s temperature. This principle explains why we feel cold after bathing, why sweating cools our body, and why earthen pots keep water cool. The NCERT PDF contains numerical problems where students calculate cooling effects using latent heat values.

For students interested in thermal concepts, the Calorimetry PDF for ICSE Class provides additional practice problems on heat transfer and latent heat calculations.

Kinetic Theory and Particle Motion

The kinetic theory of matter forms the theoretical backbone of the entire Matter in Our Surroundings chapter. This theory explains macroscopic properties of substances using microscopic particle behaviour.

Key Postulates of Kinetic Theory

Postulate 1: Matter consists of tiny particles (atoms, molecules, or ions) that are invisible to the naked eye.

Postulate 2: These particles are in constant random motion. In solids, they vibrate; in liquids, they slide; in gases, they move freely.

Postulate 3: Particles have spaces between them. These spaces are minimum in solids, moderate in liquids, and maximum in gases.

Postulate 4: Particles attract each other with intermolecular forces. Attraction is strongest in solids and weakest in gases.

Postulate 5: Kinetic energy of particles increases with temperature. Higher temperature means faster particle motion.

Diffusion and Brownian Motion

Diffusion is the intermixing of particles of two substances due to their random motion. The NCERT PDF describes experiments with potassium permanganate in water and perfume spreading in air. Diffusion is fastest in gases, slower in liquids, and extremely slow (practically negligible) in solids.

Brownian motion—the random, zigzag movement of suspended particles—provides direct evidence for kinetic theory. This phenomenon, observed by Robert Brown in 1827 when studying pollen grains in water, proves that liquid molecules are in constant motion and collide with suspended particles from all directions.

Plasma and Bose-Einstein Condensate – Additional States

Beyond the three common states, the Matter in Our Surroundings Class 9 PDF introduces two additional states that students should understand for comprehensive knowledge.