Complete notes with real-life examples and easy explanations
Matter is anything that occupies space and has mass. Everything around us that we can see, touch, or feel is made up of matter.
Think of your school bag - it takes up space in your room and has weight. That's matter! Your books, your lunch box, even the air you breathe - all are matter. The only things that are not matter are light, sound, and feelings.
When you add sugar to water and stir it, the sugar disappears! Where did it go? The tiny sugar particles fit into the spaces between water particles. This proves that particles of matter have spaces between them.
Try this at home: Take a glass of water, add a spoon of sugar, and notice how the water level doesn't rise much. The sugar particles occupy the empty spaces between water particles!
Matter exists in three main states - Solid, Liquid, and Gas. The difference between these states is due to the arrangement and movement of particles.
Solids have a fixed shape and fixed volume. The particles in solids are very tightly packed and can only vibrate in their positions.
Imagine students standing in a morning assembly - everyone in a fixed position, very close together, and can only move a little bit. That's how particles are in solids! Examples: Your desk, pencil, book, stone, ice.
Liquids have fixed volume but no fixed shape. They take the shape of the container they are poured into. Particles in liquids are less tightly packed than solids.
Imagine children in a playground - they are close to each other but can move around freely and slide past one another. That's how particles behave in liquids! Examples: Water, milk, juice, oil.
Gases have neither fixed shape nor fixed volume. They spread out to fill the entire space available to them. Particles in gases are far apart from each other.
Imagine children running freely in a large ground - they are far apart and move in all directions with high speed. That's how particles behave in gases! Examples: Air, oxygen, carbon dioxide, perfume vapor.
When someone sprays perfume in one corner of a room, you can smell it in another corner within seconds. This is because perfume particles (gas) move very fast and spread throughout the room. This property is called diffusion.
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed shape | No fixed shape | No fixed shape |
| Volume | Fixed volume | Fixed volume | No fixed volume |
| Particle Arrangement | Very closely packed | Less closely packed | Very far apart |
| Particle Movement | Only vibrate | Can slide past each other | Move freely and randomly |
| Compressibility | Cannot be compressed | Slightly compressible | Highly compressible |
| Density | Very high | Medium | Very low |
| Flow | Cannot flow | Can flow | Can flow |
Matter can change from one state to another by changing temperature or pressure. These changes are called interconversion of states of matter.
When we heat a solid, its particles gain energy and vibrate faster. At a certain temperature called the melting point, the solid changes into liquid. Example: Ice melts into water at 0°C.
When we cool a liquid, its particles lose energy and slow down. At a certain temperature called the freezing point, the liquid changes into solid. Example: Water freezes into ice at 0°C.
When we heat a liquid, its particles gain energy and move faster. At a certain temperature called the boiling point, the liquid changes into gas. Example: Water boils and converts to steam at 100°C.
When we cool a gas, its particles lose energy and slow down. The gas changes back into liquid. Example: Water vapor in air condenses to form water droplets on a cold surface.
Some substances change directly from solid to gas without becoming liquid. This process is called sublimation. Example: Camphor, naphthalene balls, dry ice (solid CO₂).
The water cycle is the best example of interconversion of states! Water in rivers evaporates to form water vapor (liquid to gas), rises up in the sky, cools down to form clouds (gas to liquid), and falls back as rain (liquid). In cold regions, it can fall as snow (solid).
You might have noticed that naphthalene balls (mothballs) kept in cupboards become smaller and smaller and finally disappear. This happens because naphthalene undergoes sublimation - it changes directly from solid to gas without melting!
By applying pressure and reducing temperature, gases can be liquefied. For example, LPG (Liquefied Petroleum Gas) is stored in cylinders under high pressure as a liquid. When you open the gas stove, the pressure decreases and LPG comes out as gas.
Evaporation is the process of changing liquid into vapor at any temperature below its boiling point. It happens at the surface of the liquid.
Imagine wet clothes drying on a clothesline. The water doesn't boil, yet it disappears! This is evaporation. The water particles at the surface gain enough energy from sunlight and air to escape as vapor.
When we sweat, the water on our skin evaporates. Evaporation is a cooling process - it takes heat from our body to convert water into vapor. This makes us feel cool!
That's why: We pour water on ground during summers, we use coolers, and we splash water on our face to feel fresh!
| Evaporation | Boiling |
|---|---|
| Happens at any temperature | Happens at a specific temperature (boiling point) |
| Happens only at the surface | Happens throughout the liquid |
| Slow process | Fast process |
| Causes cooling | Requires continuous heating |
| Example: Clothes drying | Example: Water boiling in a kettle |
1. Temperature remains constant during change of state (melting,
boiling, freezing)
2. Evaporation causes cooling
3. Particles of matter are always in motion
4. Gases can be liquefied by applying pressure and lowering
temperature
5. Kelvin is the SI unit of temperature: K = °C + 273
Q1. Why do we feel cold when we apply nail polish
remover or perfume on our hand?
Answer: Nail polish remover evaporates quickly,
taking heat from our hand, making it feel cold.
Q2. Why do gases fill completely the vessel in
which they are kept?
Answer: Because particles of gases have high
kinetic energy and weak forces of attraction, they move freely and
occupy all available space.
Q3. Why is ice at 0°C more effective in cooling
than water at 0°C?
Answer: Ice at 0°C absorbs latent heat to melt
into water, thus absorbing more heat from the surroundings and
providing better cooling.