1. Physical Nature of Matter
Everything around us, like air, food, or a drop of water, is made of matter. Matter is anything that has mass and takes up space (volume). Ancient philosophers, both Indian and Greek, classified matter into five elements: air, earth, fire, sky, and water. Today, we study matter based on its physical and chemical properties.
Key Idea: Matter is made of tiny particles! These particles are so small that even a single crystal of something like potassium permanganate can color a huge amount of water (1000 liters!). This shows how tiny and numerous these particles are.
Fun Fact: If you dissolve salt in water, it seems to disappear, but it’s just spread out among water particles!
2. Characteristics of Particles of Matter
- Space Between Particles: Particles have spaces between them, which is why sugar or salt can dissolve in water by fitting into those spaces.
- Constant Motion: Particles are always moving! This movement is called kinetic energy. When you heat something, particles move faster, which is why hot tea mixes faster than cold tea.
- Attraction: Particles attract each other. This force is strongest in solids (like an iron nail), weaker in liquids (like water), and weakest in gases (like air).
Activity: Smell an unlit incense stick, then light it. Notice how the smell spreads faster when it’s lit!
3. States of Matter
Matter exists in three states: solid, liquid, and gas. These states depend on how particles are arranged and how they move.
3.1 Solid State
Solids have a fixed shape and volume. Their particles are tightly packed, vibrate in place, and are hard to compress. Examples: a pen, a book.
3.2 Liquid State
Liquids have a fixed volume but no fixed shape. They take the shape of their container and flow easily. Examples: water, juice.
3.3 Gaseous State
Gases have no fixed shape or volume. They spread to fill their container and are highly compressible. Examples: air, LPG.
Visualize: Imagine particles in solids as students sitting still in a classroom, liquids as students moving in a hallway, and gases as students running freely on a playground!
4. Changing States of Matter
Matter can change from one state to another by changing temperature or pressure.
4.1 Effect of Temperature
Heating a solid increases particle movement, turning it into a liquid at its melting point (e.g., ice melts at 0°C). Heating a liquid turns it into a gas at its boiling point (e.g., water boils at 100°C). The heat used to change state without raising temperature is called latent heat.
4.2 Effect of Pressure
Increasing pressure can turn gases into liquids (e.g., LPG in cylinders). Some substances, like dry ice, change directly from solid to gas (sublimation) or gas to solid (deposition).
Try This: Heat ice and watch it melt, then boil. Notice how the temperature stays constant during melting and boiling!
5. Evaporation
Evaporation is when a liquid turns into vapor below its boiling point. It happens when surface particles gain enough energy to escape.
5.1 Factors Affecting Evaporation
- Surface Area: Larger surface = faster evaporation (e.g., spreading wet clothes).
- Temperature: Higher temperature = faster evaporation.
- Humidity: Lower humidity = faster evaporation.
- Wind Speed: Faster wind = faster evaporation.
5.2 Evaporation Causes Cooling
When particles evaporate, they take energy from the surroundings, cooling them down. That’s why sweat cools your body or why an earthen pot keeps water cool.
Activity: Put nail polish remover on your palm and feel the cooling effect!