You have picked up pebbles on a riverbank.
Where did they come from?
Rock breaks down slowly by erosion.
Flowing water carries the pieces and keeps breaking them smaller — boulder, stone, pebble.
What finally arrives is sand and clay.
Is a grain of sand the smallest piece a rock can become — or can it go smaller still?
Break a stick of chalk. Grind it to powder.
It is still chalk. How far can this go?
Grinding is a physical change. Only the size changes — never the substance.
These particles cannot be seen even with an ordinary microscope.
Are sand and clay the smallest bits of rock?
Two spoons of sugar into water. Stir.
It disappears — yet the water is sweet.
Sip from the top layer. It is sweet — so sugar is spread through the whole glass.
Water particles do not touch. There are spaces between them.
Sugar is not destroyed — only spread out.
The smallest unit of a substance. It cannot break further.
The gap between particles. Sugar hides in here.
People have wondered how far matter can be broken
since long before there were microscopes.
An ancient Indian philosopher who said matter is made of tiny, indivisible, eternal particles.
In his work the Vaisheshika Sutras · वैशेषिक सूत्र
Constituent particles pull on each other.
That pull is called interparticle attraction.
Move particles even slightly apart and the attraction drops sharply.
Strong pull → solid. Weaker → liquid. Almost none → gas.
The nature of the substance, and the distance between its particles.
An iron nail, rock salt, a stone, wood, a key,
a piece of aluminium. Look. Then hammer.
Each one has a definite shape and a definite volume. Put it down anywhere — it stays that shape.
In which of them do you think the particles are held most strongly? What did the hammer tell you?
Iron, rock salt, wood, a key.
All keep a definite shape and volume.
Particles are tightly packed with very strong attraction, fixed in position.
Only to and fro about their own position — they never slip past each other.
Ice 0 °C · Urea 133 °C · Iron 1538 °C
Heat a solid and the vibration grows. At one exact temperature the particles finally break free.
That temperature is the melting point.
Weak interparticle attraction → low melting point. Strong attraction → high melting point.
Pour 200 mL from A to B to C.
The shape changes. The level does not.
No fixed shape — but a definite volume. Particles move within a limited space.
Push a finger through water and it closes behind you. Try that with a stone.
Boiling makes bubbles throughout. Evaporation is slow, and only at the surface.
Try the same with a piece of wood.
You cannot. So how strong is the pull in a liquid?
You pushed the water aside for a moment. Lift the finger and the water closes back — nothing was cut, nothing broke.
In a liquid the attraction is a little weaker than in a solid — but still strong enough to hold the particles close together.
Both turn a liquid into vapour. But look at where and when each one happens.
Only at one temperature — the boiling point. Vapour forms inside the liquid too, which is why you see bubbles. Fast.
At any temperature, even a cold day. Only from the surface. Slow — which is why spilled water disappears overnight.
Trap incense smoke in jar A.
Open it to jar B — the smoke fills both.
A gas takes the whole space available to it, whatever the container.
Interparticle attraction is negligible. Particles move freely in every direction.
Invisible gas particles are constantly hitting the smoke, making their motion visible.
No incense stick? Leave solid iodine in a closed gas jar.
Purple vapour rises on its own and fills the whole jar — corner to corner, evenly.
Iodine vapour irritates the eyes and nose. Keep the jar closed. Do not let students handle it.
Seal a syringe of air with your thumb.
Push the plunger. It moves in.
Gas particles have large gaps between them, and pressure closes those gaps.
It will barely budge. Water is practically incompressible.
The plunger springs back — the particles push apart again.
Thumb on the nozzle. Push the plunger as hard as you like.
It will not move.
Its particles are already close together. There is almost no spare space to squeeze out.
Gas particles sit far apart, so pressure pushed them closer. Release the plunger and they spread out again.
Water at A. Add sugar → level rises to B.
Now stir it. The level drops to C.
Its volume is less than water and sugar measured separately.
Dissolved particles slip into the gaps that were already between the water particles.
The gaps in a solid are not filled with air. They contain nothing at all.
Both are solids. Both go into the same glass of water.
Yet the water level behaves in opposite ways.
Water particles are strong enough to pull sugar particles apart and slot them into the gaps. Level barely rises.
Sand particles are held together too strongly for water to pull out. They settle at the bottom and take up space — so the level rises.
Particles in a solid are packed tight and cannot travel.
But packed is not the same as touching.
"The gap must be filled with air." Almost every class says this.
There is nothing at all in it. Not air, not anything. Air is itself made of particles — it cannot fit inside a solid.
"Empty means empty."
You will hear the word in the news and in this chapter — and they are not the same thing.
In air pollution reports this means tiny dust floating in air. You can see it in a sunbeam.
In this chapter it means the building block of a substance — unimaginably smaller. One speck of dust is itself made of a huge number of them.
Minimum. Packed — but not touching.
A little more than in a solid.
Maximum. Mostly empty space.
Drop a grain of potassium permanganate into still water. Pink streaks spread on their own.
Water particles are in constant motion, even when the water looks perfectly still.
They pull particles off the grain, then knock them right through the liquid.
Hot, room, ice-cold. Pink spreads fastest in hot — heat means faster particles.
The water was still. Yet the pink reached every corner of the glass.
Water particles are in constant motion. They pull permanganate particles off the grain.
Then they keep hitting them, knocking them further and further until the colour is even.
In sand the particles are held too strongly. Water fails to pull them out — so sand is insoluble.
Hot water, room-temperature water, ice-cold water. Drop one grain of potassium permanganate into each.
Light an incense stick in one corner.
Minutes later the whole room smells of it.
Moving air particles hit the fragrance particles and push them across the room.
Its particles are held too strongly for water particles to pull them apart.
One end of a soap particle grips oil, the other holds water — lifting the stain away.
Water alone will not lift oil off cloth. Add soap and it goes.
Particles explain it.
One end grips oil. The other end mixes with water.
Many soap particles surround the oil drop, oil-end inward. The water-ends face out.
The whole ball lifts off the fabric and rinses away.
How strong the attraction feels depends on the distance between particles — and that distance depends on their thermal (heat) energy.
Particles stay close, attraction is strong, motion is cut down to small vibrations.
The added heat is spent overcoming the attraction. Particles leave their fixed positions and can move around — but only within a limited space.
Enough energy to beat the attraction completely — free in every direction.
Packed. Strong pull. Only vibrates.
Loose. Weaker pull. Flows, fixed volume.
Far apart. Almost no pull. Fills everything.
You will study this properly in higher classes.
For now, just the names.
Iron is made of iron atoms. Gold is made of gold atoms.
Some atoms cannot stay alone. Two hydrogen atoms join to make one hydrogen molecule.
Two hydrogen atoms + one oxygen atom = one water molecule.
Kanad's word for the smallest, uncuttable piece of matter — the same idea we now call the constituent particle
the force pulling constituent particles towards each other — it weakens fast with distance
the only motion a solid particle is allowed — to and fro about its own fixed position. Heat it and the vibration grows until it breaks free.
the lowest temperature at which a solid turns into a liquid at atmospheric pressure
200 mL stays 200 mL in every container — but the shape changes every time you pour
the temperature at which a liquid turns to vapour at atmospheric pressure — for water, 100 °C
they expand until they occupy every bit of the space they are given
liquids and gases together — both flow, and neither keeps a fixed shape. This is what separates them from solids.
because the space between particles is huge in a gas and tiny in a liquid
a substance whose volume will not reduce under pressure, because its particles have almost no spare space between them
largest in gases → smaller in liquids → smallest in solids
a substance whose particles water cannot pull apart, so it never spreads through the liquid — sand, stone, chalk
and the hotter they are, the faster they go
Give particles more heat and they move faster. That is the whole of this chapter in one sentence.
particles of one substance spreading right through another, with no stirring at all
If you could remove every constituent particle from a chair, what would happen? (i) Nothing changes (ii) It weighs less (iii) Nothing of the chair remains.
Why do gases mix easily, while solids do not?
Spilled milk flows and spreads across a table, but the glass tumbler it came from keeps its shape. Justify this.