NCERT Solutions for Class 8th Science Chapter 7 Particulate Nature of Matter
Updated on 2026-09-19
About this chapter
All matter is made up of an extremely large number of constituent particles — the basic units that a piece of a substance is built from. They are so small that they cannot be seen even through an ordinary microscope, and breaking or grinding a substance never changes them; it only separates one group of them from another. The particles are held together by attractive forces called interparticle attractions . Their strength depends on the nature of the substance and on the interparticle distance — even a slight increase in that distance weakens the force drastically. The strength of these attractions decides the physical state . In a solid the particles are closely packed, the attraction is strongest, and they can only vibrate about fixed positions — hence a definite shape and volume. In a
- Chapter opener
- What Is Matter Composed of?
- What Decides Different States of Matter?
- Acharya Kanad and the idea of the Parmanu
- Solid state
- Liquid state
- Gaseous state
- How Particles Move in Different States of Matter?
- End-of-chapter question set (continues on page 114)
- Society–Science interdisciplinary projects
Quick revision
| Term | What it means | Where it comes in the chapter | Example from the book |
|---|---|---|---|
| Constituent particle | The basic unit that makes up a larger piece of a substance or material | Section 7.1, page 100 | Grinding chalk on and on finally leaves the units the chalk was made of (Activity 7.1) |
| Interparticle space | The space between the constituent particles; it contains nothing at all, not even air | Sections 7.1 and 7.3, pages 101 and 109 | The level falls from B to C when sugar dissolves (Activity 7.7, Fig. 7.10) |
| Interparticle attraction | The attractive force holding the particles together; it weakens sharply as the interparticle distance grows | Section 7.2, page 101 | Strongest in a piece of iron, weaker in water, negligible in air |
| Solid state | Definite shape and volume; particles closely packed, attraction strongest, motion only vibration about fixed positions | Section 7.2.1, page 102 | Iron nail, rock salt, stone, key, wooden block, aluminium (Fig. 7.3) |
| Liquid state | Definite volume, no fixed shape; particles free to move but only within a limited space | Section 7.2.2, page 104 | The same 200 mL of water in containers A, B and C (Activity 7.4, Fig. 7.5) |
| Gaseous state | Neither fixed shape nor fixed volume; attraction negligible, particles move freely in all directions | Section 7.2.3, page 106 | Smoke fills the whole of Gas Jar B (Activity 7.5, Fig. 7.7) |
| Melting point | The minimum temperature at which a solid melts into a liquid at atmospheric pressure | Section 7.2.1, page 103 | Ice 0 °C, urea 133 °C, iron 1538 °C (Table 7.1) |
| Boiling point | The temperature at which a liquid boils and turns into vapour at atmospheric pressure | Section 7.2.2, page 105 | Bubbles form inside the liquid, not only at its surface |
| Evaporation | The slow change of a liquid into vapour, at any temperature and only from the surface | Section 7.2.2, page 105 | Spilled water disappears after some time |
| Fluids | Liquids and gases together — they flow and do not keep a fixed shape | Section 7.2.3, page 106 | Water poured from one container to another; smoke spreading in a gas jar |
| Thermal energy | The heat energy of the particles; it decides how far apart they stay, and hence the state of the substance | Let us wrap up, page 112 | Low in solids, more in liquids, highest in gases |
| Suspended Particulate Matter (SPM) | Tiny dust particles suspended in air — not constituent particles; each dust particle is itself made of a huge number of atoms and molecules | A step further, page 109 | The term used when talking about air pollution |
Exercises
- Chapter opener — Probe and ponder Page 98
- In-text Questions — What Is Matter Composed of? Page 99
- Activity 7.1: Let us explore — What Is Matter Composed of? Page 99
- In-text Questions — What Is Matter Composed of? Page 100
- Activity 7.2: Let us perform — What Is Matter Composed of? Page 100
- In-text Questions — What Decides Different States of Matter? Page 101
- Acharya Kanad and the idea of the Parmanu — Our scientific heritage Page 101
- In-text Questions — Solid state Page 102
- Activity 7.3: Let us find out — Solid state Page 102
- In-text Questions — Solid state Page 103
- In-text Questions — Liquid state Page 104
- In-text Questions — Gaseous state Page 105
- In-text Questions — How Does the Interparticle Spacing Differ in the Three States of Matter? Page 107
- Activity 7.6: Let us experiment — How Does the Interparticle Spacing Differ in the Three States of Matter? Page 107
- Activity 7.7: Let us observe — How Does the Interparticle Spacing Differ in the Three States of Matter? Page 108
- In-text Questions — How Does the Interparticle Spacing Differ in the Three States of Matter? Page 108
- In-text Questions — How Does the Interparticle Spacing Differ in the Three States of Matter? Page 109
- Activity 7.8: Let us experiment — How Particles Move in Different States of Matter? Page 109
- Think like a scientist — How Particles Move in Different States of Matter? Page 110
- In-text Questions — How Particles Move in Different States of Matter? Page 110
- Activity 7.9: Let us find out — How Particles Move in Different States of Matter? Page 110
- In-text Questions — How Particles Move in Different States of Matter? Page 111
- End-of-chapter question set (continues on page 114) — Keep the curiosity alive Page 113
- Society–Science interdisciplinary projects — Discover, design, and debate Page 115