Matter is made of tiny particles
A spoon of sugar disappears in a glass of water, yet the first sip is sweet. Where did the sugar go? A grinding stone turns a hard lump of chalk into soft dust. Both everyday happenings give us a clue about what matter is made of.
All matter is made of a very large number of extremely small units called constituent particles. The empty gaps between them are the interparticle spaces. This is the particulate nature of matter.
Key idea 1: Break it again and again — Crush a lump of chalk into pieces, then into powder. Each speck is still chalk, only smaller. If we could keep dividing, we would finally reach the tiny constituent particles that cannot be seen even with an ordinary microscope. Acharya Kanad, an ancient Indian thinker, imagined such tiny units and called them Parmanu.
- Easy: Grinding chalk into powder only makes the pieces smaller; no new substance is formed.
- Medium: Every grain of sand is itself made of a huge number of constituent particles.
- Exam-type: A lump of chalk is ground into powder. This is a physical change, because the powder is still chalk made of the same particles.
In the figure: Each step makes the pieces smaller, and the last step reaches the tiny particles.
Key idea 2: Particles hide in the gaps — When sugar is stirred into water, the sugar breaks into constituent particles that move into the interparticle spaces of water. We cannot see sugar any more, but the sweet taste shows that it is still there. Without stirring, the top layer stays less sweet because the particles have not spread yet.
- Easy: Sweet water proves that the sugar particles are present in it.
- Medium: Dissolved salt does not vanish; when the water dries up, white salt crystals are left behind.
- Exam-type: A glass full to the brim takes a pinch of salt without spilling, because the salt particles fit into the gaps between the water particles.
In the figure: We cannot see the particles, but their effect, the sweet taste, tells us they are there.
Matter is made of tiny constituent particles with interparticle spaces between them.
Saying that dissolved sugar has disappeared. It is only broken into tiny particles mixed with water.
If it tastes or smells, the particles are there even when unseen. Memory clue: Particles Pack in Pieces, Spaces Sit between.
Spot the difference
| Term | Meaning | Example |
|---|---|---|
| constituent particle | basic tiny unit of matter | a particle of sugar |
| interparticle space | empty gap between particles | gaps in water |
| dust speck | a crowd of many particles | chalk powder grain |
Practice questions
- 1What are the tiny units that make up matter called?
- 2What are the empty gaps between particles called?
- 3Who was Acharya Kanad?
- 4Why does the water taste sweet even though sugar cannot be seen?
- 5Is a grain of fine chalk powder a single constituent particle? Explain.
- 6Why does stirring help sugar spread in water?
- 7Arrange in increasing order of size: a chalk dust speck, a constituent particle of chalk, a pebble.
- 8A friend says that salt destroyed itself when it dissolved. Use a simple activity to show that she is wrong.
Show answers (try them yourself first)
- 1Constituent particles.
- 2Interparticle spaces.
- 3An ancient Indian thinker who spoke of tiny indivisible units called Parmanu.
- 4The sugar has broken into constituent particles that are spread through the water, so the water tastes sweet.
- 5No. Each speck is made of a very large number of constituent particles; it only looks like a tiny piece.
- 6Stirring moves the particles so that they spread through the whole water faster.
- 7Constituent particle of chalk, chalk dust speck, pebble.
- 8Dissolve salt in water and taste it: the water is salty. Then let the water dry up; white salt appears again. So the salt was present all the time as tiny particles.
Interparticle attraction and the solid state
A steel spoon stays the same shape whether it lies in a plate, in a bowl or on a table. A wax candle, on the other hand, softens near a flame. Why do some solids hold together far more strongly than others?
Particles of matter attract one another. This pull is called interparticle attraction. In a solid the attraction is strong, so the particles are held close together in fixed positions and the solid has a definite shape and a definite volume.
Key idea 1: Fixed positions, tiny vibrations — The particles of a solid cannot slide past one another. They only vibrate in place. The gaps between them are very small, so a solid is rigid and very hard to squeeze.
- Easy: A solid has a definite shape and a definite volume.
- Medium: A solid does not flow when its container is tilted, because its particles stay in fixed places.
- Exam-type: A solid is hard to compress because its particles are already close together with very little space left to squeeze.
In the figure: In the solid box the particles sit tightly in rows; in the liquid they slide; in the gas they are far apart.
Key idea 2: Melting point tells the strength — When a solid is heated, its particles vibrate more. At a particular temperature, called the melting point, they gain enough energy to slide past one another and the solid becomes a liquid. A higher melting point means a stronger interparticle attraction.
- Easy: The temperature at which a solid turns into a liquid is its melting point.
- Medium: Wax melts at about 60 °C and iron at about 1500 °C, so iron has the stronger attraction.
- Exam-type: Substances P, Q and R melt at 45 °C, 700 °C and 120 °C. In increasing order of attraction they are P, R, Q.
In the figure: The taller the bar, the stronger the pull between the particles.
Strong attraction, fixed positions, definite shape and volume: this is a solid.
Thinking that the particles of a solid do not move at all. They vibrate in place.
Compare melting points: higher means stronger attraction. Memory clue: High Melt = Hard Hold.
Spot the difference
| Feature | Solid | Why |
|---|---|---|
| shape | definite | particles fixed |
| gaps | very small | tightly packed |
| movement | only vibrates | strong attraction |
Practice questions
- 1What is the pull between particles called?
- 2Name two features of the solid state.
- 3What is the melting point?
- 4Why does an iron nail keep its shape in any bowl?
- 5A candle softens near a flame, but an iron rod does not. Why?
- 6How do the particles move in a solid?
- 7Substances A and B melt at 80 °C and 300 °C. Which has the stronger attraction? Give a reason.
- 8A steel spoon stays solid in tea at 80 °C, but ice melts in the palm. Explain using melting points.
Show answers (try them yourself first)
- 1Interparticle attraction.
- 2Definite shape and definite volume (also very small gaps, hard to compress).
- 3The temperature at which a solid changes into a liquid.
- 4Strong attraction holds its particles in fixed positions.
- 5Wax has weaker attraction and a low melting point; iron has stronger attraction and a very high melting point.
- 6They only vibrate about their fixed positions.
- 7B, because it needs a higher temperature to melt.
- 8Steel melts at a temperature far above 80 °C, so it stays solid; ice melts at 0 °C, which is below the palm temperature.
The liquid state, boiling and evaporation
Milk poured from a packet into a bowl takes the shape of the bowl, but the quantity of milk does not change. A wet towel on the line dries even on a cool morning, though nobody heats it.
A liquid has a definite volume but no fixed shape; it takes the shape of its container. Its particles are close but weakly held, so they can slide past one another. Liquids and gases together are called fluids because they can flow.
Key idea 1: Close but free to slide — The gaps in a liquid are a little larger than in a solid. Particles stay close, so the volume is fixed, but they move around, so the shape is not fixed. This is why a liquid flows and is not rigid.
- Easy: Juice poured from a jug into a tall glass changes its shape but not its volume.
- Medium: A liquid cannot be called rigid because its particles slide and it cannot keep its own shape.
- Exam-type: Water boils at about 100 °C and alcohol at about 78 °C, so alcohol has the weaker interparticle attraction.
In the figure: Boiling is fast at a fixed temperature, and evaporation is slow but always possible.
The liquid state, boiling and evaporation
In the app you can move this figure with your finger.
Open in the appKey idea 2: Boiling and evaporation — At the boiling point a liquid changes quickly into vapour all through its body. Evaporation is the slow change from the surface at any temperature. A wide surface, heat and moving air speed it up.
- Easy: Wet clothes dry in the sun because the water in them evaporates.
- Medium: The same water dries sooner in a wide plate than in a narrow glass, because more surface is open to the air.
- Exam-type: A substance melts at -10 °C and boils at 80 °C; at 25 °C it is a liquid, because 25 °C lies between the two points.
In the figure: Particles leave from the surface one by one, so no boiling is needed.
Liquid: fixed volume, no fixed shape, particles slide. Fluids are liquids and gases.
Thinking that water changes into vapour only at 100 °C. Evaporation happens at every temperature.
For the state at a given temperature, check below melting, between, or above boiling. Memory clue: Below Melt = Solid, Between = Liquid, Above Boil = Gas.
Spot the difference
| Feature | Boiling | Evaporation |
|---|---|---|
| temperature | fixed | any |
| where | whole liquid | surface only |
| speed | fast | slow |
Practice questions
- 1Does a liquid have a fixed shape?
- 2Name the two kinds of fluids.
- 3Why do wet clothes dry in the sun?
- 4Why can a liquid flow but a solid cannot?
- 5Why does water in an open bowl reduce over several days without being heated to 100 °C?
- 6Give two differences between boiling and evaporation.
- 7A substance melts at 30 °C and boils at 150 °C. What is its state at 100 °C and at 20 °C?
- 8Equal water is kept in a wide plate and in a narrow glass on a windy day. Which dries first and why?
Show answers (try them yourself first)
- 1No. A liquid takes the shape of its container.
- 2Liquids and gases.
- 3The water in them evaporates and leaves as vapour.
- 4Its particles are weakly held and can slide past one another, while a solid's particles are fixed.
- 5Evaporation from the surface takes place at any temperature.
- 6Boiling is at a fixed temperature through the whole liquid and is fast; evaporation is at any temperature from the surface and is slow.
- 7At 100 °C it is a liquid; at 20 °C it is a solid.
- 8The plate, because more surface is exposed, and wind carries the vapour away.
The gaseous state and interparticle spaces
A cooking gas cylinder holds a huge amount of gas in a small steel body. A bicycle pump squeezes a big volume of air into a tyre. Yet nobody can squeeze a bottle of water into a smaller space.
A gas has no fixed shape and no fixed volume; it spreads to fill any container. Its particles are far apart, the attraction between them is very weak, and they move rapidly in all directions.
Key idea 1: Large gaps, easy to compress — The spaces between gas particles are very large, so a gas can be compressed easily. In a sealed syringe, the plunger moves in a long way when it holds air, but hardly moves when it holds water.
- Easy: Air can be squeezed easily by pushing the plunger of a sealed syringe.
- Medium: Solids hardly compress, liquids compress very little, and gases compress a lot.
- Exam-type: Increasing order of ease of compression: solid, liquid, gas.
In the figure: The same push moves the plunger in far more when the syringe holds air.
Key idea 2: What lies in the gaps? — The gaps are empty; there is nothing in them, not even more air. When sugar or salt dissolves in water, its particles go into the gaps between water particles, so the water level rises only very slightly. Air pollution experts talk about SPM, suspended particulate matter: dust bits floating in air, each one a crowd of countless constituent particles.
- Easy: The spaces between the particles of air are empty.
- Medium: A little salt can be added to a brim-full glass of water without spilling, because it fits into the gaps.
- Exam-type: SPM dust is visible in a beam of light, but the constituent particles of air are far too small to see.
In the figure: The gaps grow from solid to liquid to gas, so the gas is the easiest to press.
Gas: no fixed shape or volume, large gaps, weak attraction, easy to compress.
Thinking that the gaps between air particles hold more air. They are empty.
The larger the gaps, the easier the squeeze. Memory clue: Gas = Gaps Galore.
Spot the difference
| Feature | Solid | Liquid | Gas |
|---|---|---|---|
| shape | fixed | no fixed shape | no fixed shape |
| volume | fixed | fixed | not fixed |
| gaps | tiny | small | large |
Practice questions
- 1What fills the gaps between air particles?
- 2Which state is the easiest to compress?
- 3What does SPM stand for?
- 4Why can a gas fill any container?
- 5Why does a cooking gas cylinder hold so much gas?
- 6Why does the water level rise only a little when sugar dissolves?
- 7Arrange in increasing size of gaps: gas, solid, liquid.
- 8SPM bits float in air, yet the particles of air cannot be seen. Explain.
Show answers (try them yourself first)
- 1Nothing; the gaps are empty.
- 2The gaseous state.
- 3Suspended Particulate Matter.
- 4Its particles are far apart, attract very weakly and move freely in all directions.
- 5Gas can be compressed because of the large gaps between its particles.
- 6Sugar particles go into the gaps between water particles.
- 7Solid, liquid, gas.
- 8An SPM bit is dust made of countless constituent particles, so it is much bigger than a single particle of air.
Movement of particles and thermal energy
When a neighbour starts cooking, the smell reaches your house in a few minutes. A drop of ink dropped in still water slowly colours the whole glass. Nobody stirred, yet the colour and the smell spread.
The particles of matter are always moving. The natural spreading of one substance into another is called diffusion. The thermal energy of the particles depends on temperature: more heat makes them move faster.
Key idea 1: Diffusion proves motion — A crystal of potassium permanganate colours water slowly because its particles move into the water on their own. Incense smell spreads through the air in the same way. Diffusion is fastest in gases, slower in liquids and very slow in solids.
- Easy: The fragrance of an incense stick reaches the whole room by diffusion.
- Medium: Ink spreads faster in hot water than in cold water, because the particles move faster at a higher temperature.
- Exam-type: Diffusion in solids is very slow, because the particles are held in fixed positions by strong attraction.
In the figure: The coloured particles slowly move into the gaps between the water particles until they are evenly spread.
Key idea 2: Thermal energy decides the state — Heat a solid and its particles move faster. At the melting point they slide, and it becomes a liquid. At the boiling point they break free and it becomes a gas. Cool a gas and the particles slow down, come together and form a liquid.
- Easy: Heating a substance gives its particles more thermal energy.
- Medium: Sugar dissolves faster in hot tea than in cold tea, because the particles move faster and mix sooner.
- Exam-type: In increasing thermal energy per particle: ice at -10 °C, water at 30 °C, steam at 110 °C.
In the figure: Each step shows particles with more energy and less hold on one another.
Particles are always moving; diffusion and heat both prove it.
Saying that only gas particles move. Particles in solids and liquids also move, only less freely.
More heat, faster particles, quicker spreading. Memory clue: Hot = Hurry.
Spot the difference
| State | Particle motion | Diffusion |
|---|---|---|
| solid | vibrates in place | very slow |
| liquid | slides around | slow |
| gas | moves rapidly everywhere | fast |
Practice questions
- 1What is the spreading of one substance into another called?
- 2What happens to particles when the temperature rises?
- 3Name one everyday example of diffusion.
- 4Why does ink spread faster in hot water?
- 5Why is diffusion very slow in solids?
- 6What happens to a gas when it is cooled strongly?
- 7Arrange in increasing thermal energy per particle: steam at 110 °C, ice at -10 °C, water at 30 °C.
- 8How does diffusion support the idea of gaps between particles?
Show answers (try them yourself first)
- 1Diffusion.
- 2They move faster.
- 3The smell of cooking food reaching neighbours (or fragrance of an incense stick).
- 4Particles move faster at a higher temperature, so they mix sooner.
- 5Solid particles are held in fixed positions and cannot wander.
- 6Its particles slow down, come closer and may form a liquid.
- 7Ice at -10 °C, water at 30 °C, steam at 110 °C.
- 8Particles of one substance move into the gaps between particles of another; mixing would be impossible without gaps.
Movement of particles and thermal energy
In the app you can move this figure with your finger.
Open in the app