Particulate Nature of Matter – Class 8 Science Chapter 7 Notes & NCERT PDF

Class 8ScienceChapter 7NCERT book: Curiosity - Science Class 8

Notes and a simple summary of Chapter 7 of the NCERT Class 8 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

🎧 Listen to the content

Chapter 7: Particulate Nature of Matter

Probe and Ponder

The chapter opens with puzzles from daily life:

Why can we pile up stones or sand, but not water?

Why does water take the shape of folded hands, but lose that shape when released?

We cannot see air, so how does it add weight to an inflated balloon?

By the end of the chapter, you will be able to answer all of these using one big idea: matter is made of tiny particles.

Introduction

Rivers flowing through mountains break rocks into pebbles, stones and sand, and carry them to the plains. Bigger rocks finally become fine grains of sand and clay. But is a grain of sand the smallest unit of a rock? Or can it be broken down further? This chapter follows that question all the way down.

Key Concepts

7.1 What is matter composed of?

If you keep breaking and grinding a stick of chalk, every tiny speck is still chalk. Grinding is a physical change, only the size gets smaller.

If we imagine grinding forever, we finally reach units that cannot be broken any further. These are the constituent particles of chalk.

A constituent particle is the basic unit that makes up a larger piece of a substance or material.

When sugar dissolves in water, you can no longer see it, but the water tastes sweet. The sugar has broken up into its constituent particles. Each tiny grain of sugar contains millions and millions of them.

These particles are so small that they cannot be seen even through an ordinary microscope.

The sugar particles fit into the gaps between water particles. These gaps are called interparticle spaces.

7.2 What decides the state of matter?

Particles are held together by attractive forces called interparticle attractions.

Their strength depends on the nature of the substance and the distance between particles. Even a slight increase in distance weakens them drastically.

The strength of these forces decides whether a substance is a solid, liquid or gas.

Our scientific heritage: Acharya Kanad, an ancient Indian philosopher, first spoke of the Parmanu (atom): tiny, indivisible, eternal particles that make up matter. He wrote about it in the Vaisheshika Sutras.

#### Solid state

Particles are tightly packed with very strong attractions, held in fixed positions.

They can only vibrate (move to and fro) about their positions, not move past each other.

So solids have a definite shape and volume.

On heating, vibrations increase until particles leave their positions and the solid becomes a liquid.

The minimum temperature at which a solid melts to become a liquid at atmospheric pressure is its melting point.

Examples from the book: ice 0 °C, urea 133 °C, iron 1538 °C. Weak attractions mean a low melting point; strong attractions mean a high one.

Particles in a liquid are usually a little farther apart than in the solid. Ice is an exception: its particles are farther apart than in water.

#### Liquid state

Water poured from container A to B to C (200 mL each) changes shape but stays at 200 mL. Liquids have no fixed shape but a fixed volume.

You can move your finger through water; it closes back behind it. Attractions are slightly weaker than in solids but still keep particles close.

The temperature at which a liquid boils and turns into vapour at atmospheric pressure is its boiling point.

At the boiling point, vapour forms fast, inside the liquid too (bubbles).

Evaporation happens at all temperatures, but slowly and only at the surface.

#### Gaseous state

Smoke trapped in one gas jar spreads to fill a second jar placed over it. Gases have no fixed shape or volume.

Particles move freely in all directions; attractions are negligible.

Liquids and gases both flow and do not keep a fixed shape, so both are called fluids.

7.3 Interparticle spacing in the three states

Syringe test: air in a closed syringe can be pushed into a smaller volume, so gas particles have a lot of space between them. Water is practically incompressible.

Sugar in water: the level rises when sugar is added, but may fall a little after it dissolves, because sugar particles fill the spaces between water particles.

Sand does not dissolve; it just settles and the volume goes up.

Even in solids there is some space between particles, and that space contains nothing at all, not even air.

7.4 How particles move

A grain of potassium permanganate in water first gives pink streaks, then the whole tumbler turns uniformly pink, because water particles are always moving.

In hot water it spreads fastest; slower at room temperature; slowest in ice-cold water. Heat increases particle movement.

The fragrance of an incense stick lit in one corner soon fills the room, because air particles are constantly moving and carry the fragrance particles.

Ever heard of: soap particles surround oil on a fabric. One end sticks to the oil and the other mixes with water, lifting the oil away.

The big picture: thermal energy decides the state

Solid: low thermal energy, strong attractions, only vibration.

At the melting point: energy overcomes attractions; particles can move about in a limited space.

Gas: enough energy to overcome attractions; particles move freely everywhere.

In summary:

Spacing: minimum in solids, a little more in liquids, maximum in gases.

Attraction: maximum in solids, slightly weaker in liquids, negligible in gases.

Movement: only vibrations in solids, limited space in liquids, all available space in gases.

Activities in the Chapter

Activity 7.1 (chalk): Break and grind chalk and look at it with a magnifying glass. Observation: every speck is still chalk. Conclusion: matter is made of very many tiny particles.

Activity 7.2 (sugar): Taste the top layer before and after stirring. Observation: sweet only after dissolving. Conclusion: sugar broke into invisible particles spread through the water.

Activity 7.3 (solids): Observe and hammer an iron nail, rock salt, stone, wood, key and aluminium. Conclusion: particles are strongly held, giving definite shape and volume.

Activity 7.4 (containers A, B, C): Pour 200 mL of water between three differently shaped containers. Conclusion: the shape changes, the volume stays the same.

Activity 7.5 (smoke / iodine vapour): Smoke from jar A fills jar B. Conclusion: gases occupy all available space.

Activity 7.6 (syringe): Compress air and then water. Conclusion: gases are compressible; water practically is not.

Activity 7.7 (water level): Mark levels A, B, C before and after dissolving sugar. Conclusion: particles of the solute occupy interparticle spaces.

Activity 7.8 (potassium permanganate): Watch the colour spread, faster in hot water.

Activity 7.9 (incense stick): Fragrance spreads through the room.

Key Terms

Matter (पदार्थ): anything that has mass and occupies space

Constituent particle (घटक कण): the basic unit making up a substance

Interparticle space (अंतराकणिक स्थान): gap between particles

Interparticle attraction (अंतराकणिक आकर्षण): force holding particles together

Melting point (गलनांक): temperature at which a solid melts at atmospheric pressure

Boiling point (क्वथनांक): temperature at which a liquid boils at atmospheric pressure

Evaporation (वाष्पीकरण): slow vapour formation at the surface, at any temperature

Vibrate (कंपन करना): move to and fro about a fixed position

Compressible (संपीड्य): can be squeezed into a smaller volume

Fluid (तरल): a substance that flows (liquids and gases)

Parmanu (परमाणु): Kanad's idea of an indivisible particle

Thermal energy (ऊष्मीय ऊर्जा): heat energy of particles

Real-life Connections

You smell perfume or food from a distance because gas particles move and spread.

Tea sugar "disappears" but still sweetens every sip.

Gas cylinders hold a lot of gas because gases can be compressed.

Soap removes oil stains by surrounding the oil particles.

Common Misconceptions

❌ "The space between particles is filled with air." ✅ It contains nothing at all.

❌ "Evaporation happens only at the boiling point." ✅ It happens at all temperatures, at the surface.

❌ "Sand and rice are liquids because they take the shape of the jar." ✅ Each grain keeps its shape; they are solids.

❌ "Ice particles are closer than water particles." ✅ Ice is the exception; its particles are farther apart.

❌ "Dust particles (SPM) are constituent particles." ✅ Dust is itself made of a very large number of constituent particles (atoms and molecules).

Keep the Curiosity Alive (hints)

Q1: Particles are closely packed in solids and move past each other in liquids.

Q3: If all constituent particles were removed, nothing of the chair would remain; the chair is its particles.

Q4: Gas particles have large spaces and negligible attractions, so they mix easily; solid particles are fixed.

Q9: Salt is dissolved into invisible particles spread through the seawater.

Q10: Rice grains and flour are solids; each grain keeps its own shape and volume.

💡 Key Learning Points

✓Matter is made of extremely small constituent particles that cannot be seen even with an ordinary microscope.
✓Interparticle attractions are strongest in solids, slightly weaker in liquids and negligible in gases.
✓Interparticle spacing is minimum in solids, a little more in liquids and maximum in gases, which explains compressibility.
✓Particles are always moving; heating increases their motion (potassium permanganate spreads fastest in hot water).
✓Thermal energy of the particles decides the state of matter, from vibration in solids to free movement in gases.

👨‍🏫 Teaching Tips

→Do the chalk-grinding and sugar-tasting activities first, so the idea of invisible particles comes from students' own senses.
→Run the three-tumbler potassium permanganate race (hot, room temperature, ice-cold) and let students predict the winner before watching.
→Use a needle-less syringe to let every student feel air compress and water resist.
→Have students act as particles: stand tightly and sway (solid), shuffle close together (liquid), move freely across the room (gas).
→Build clay-ball or bead models of the three states showing spacing, as suggested in 'Discover, design, and debate'.
→Tell the story of Acharya Kanad and the Vaisheshika Sutras to connect the particle idea to India's scientific heritage.
→Address the 'empty space contains air' misconception directly with a quick class vote and discussion.

📋 Assessment Questions

Can the student explain, using particles, why water takes the shape of its container but keeps its volume?
Can the student compare spacing, attraction and movement of particles across solid, liquid and gas?
Can the student explain why the water level may drop slightly after sugar dissolves?
Can the student distinguish evaporation from boiling?
Can the student draw particle diagrams of ice melting and then changing into vapour?

Ask the AI tutor about Class 8 Science Chapter 7

Get question answers, important questions, a quick MCQ quiz or a simple explanation of “Particulate Nature of Matter”. Free — sign in with Google.

How the AI tutor works →

👩‍🏫 Class 8 Science classes near you — online or at home

Prefer a real teacher? TalentJR teachers take live online classes anywhere in India and visit homes in selected cities. Tell us what you need and our team will call you with timings and fees.

Live online classesSmall groups or 1:1 with a teacher, from home, any city.
Teacher at homeA TalentJR teacher visits your home (selected cities).
At a centreClasses at a TalentJR partner centre near you, where available.

Keep learning

← Previous: Chapter 6Pressure, Winds, Storms, and Cyclones Next: Chapter 8 →Nature of Matter: Elements, Compounds, and Mixtures