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Matter in our surroundings - class 9th

Matter in Our Surroundings - Class 9th

Have you ever wondered why ice melts, steam disappears, or why your clothes dry faster on a windy day? All of these daily wonders are linked to a fascinating scientific concept: Matter. In Class 9 Science, the first chapter “Matter in Our Surroundings” lays the foundation of Chemistry by explaining the physical nature of everything around us.
Let’s explore this chapter in a way that’s not just educational but also fun and relatable!

What is Matter?

Matter is anything that occupies space and has mass. Whether it’s the air you breathe, the water you drink, or the phone in your hand – all of it is matter.

Activity: Fill a balloon with air – it becomes bigger and heavier. That’s because air too is matter!

Physical Nature of Matter

The physical nature of matter explains the basic structure, behavior, and characteristics of matter based on its observable and microscopic properties. Let’s break it down into clear, easy-to-understand points:

1. Matter is Made Up of Particles

  • All matter—whether solid, liquid, or gas—is composed of tiny particles that are too small to be seen with the naked eye.
  • These particles could be atoms or molecules depending on the substance.

Example: When you dissolve sugar in water, the sugar seems to disappear, but the water still tastes sweet. This means sugar particles are still present, just too small to see.

2. The particles of matter are very small

  • Particles are so small that millions of them can fit into a pinhead.
  • Experiment:
    Take a beaker of water and add a few drops of ink. The color spreads throughout the water.
  • The tiny particles of ink spread and color the entire water, proving particles are extremely small.

3. Particles of matter have space between them.

  • Particles are not packed tightly; they have space in between.
  • Experiment:
    Dissolve salt in water. The level of water does not rise.
    This proves that salt particles occupy the empty spaces between water particles.

4. Particles of matter are continuously moving.

  • Particles are not at rest; they move continuously in a zig-zag manner. This random movement is called Brownian Motion.
  • Experiment:
    Light a stick of incense (agarbatti) in one corner of a room. After some time, the fragrance spreads everywhere.
    This happens due to diffusion—the movement of particles from a region of high concentration to low concentration.

5. Particles of matter attract each other.

  • There is a force of attraction between particles of matter. The strength of this force differs in solids, liquids, and gases.
  • In solids, particles are tightly packed → strong force of attraction.
  • In liquids, particles are less tightly packed → moderate attraction.
  • In gases, particles are far apart → negligible attraction.
  • Experiment:
    Try to break a piece of chalk—it breaks easily (moderate attraction).
    Now try breaking a piece of iron rod—it is very hard (very strong attraction).
    This shows different substances have different forces of attraction between their particles.

States of Matter

Matter exists in three main states: Solids, Liquids, and Gases.

  1. Solids
    • Have definite shape and volume.
    • Particles are closely packed with negligible space.
    • Strong force of attraction.
    • Not compressible.
      • Example: Wood, stone, ice cube.
  2. Liquids
    • No fixed shape, but have definite volume.
    • Particles are less tightly packed.
    • Moderate force of attraction.
    • Can flow (fluid).
      • Example: Water, milk, oil.
  3. Gases
    • No fixed shape or volume.
    • Particles are far apart.
    • Weak forces of attraction.
    • Highly compressible.
      • Example: Oxygen, nitrogen, carbon dioxide.

Change of State

Matter can change from one state to another by changing temperature or pressure.

  1. Effect of Temperature
    • Solid → Liquid (Melting):
      Heat increases kinetic energy of particles → intermolecular forces weaken → solid melts.
      Example: Ice melts to water at 0°C.
    • Liquid → Gas (Evaporation/Boiling):
      Particles gain energy, overcome attraction → escape into air as vapor.
      Example: Water boils at 100°C.
    • Gas → Liquid (Condensation):
      Cooling reduces energy → particles come closer → form liquid.
      Example: Clouds/rain from water vapor.
    • Liquid → Solid (Freezing):
      Cooling reduces motion → particles set into fixed positions.
      Example: Water to ice at 0°C.
    • Solid → Gas (Sublimation):
      Some solids directly turn into vapor.
      Example: Camphor, dry ice (solid CO₂).
  2. Effect of Pressure
    • Increasing pressure brings gas particles closer → forms liquid.
    • Example: LPG cylinders contain liquid fuel under high pressure.

Evaporation and Its Factors

Slow conversion of liquid into vapor at any temperature below its boiling point.

Factors Affecting Evaporation

  1. Surface Area: Larger area → faster evaporation. (Wet clothes dry faster when spread out.)
  2. Temperature: Higher temperature → faster evaporation.
  3. Wind Speed: Higher wind speed → faster evaporation. (Fans dry clothes.)
  4. Humidity: High humidity (more water vapor in air) → slower evaporation.

Evaporation Causes Cooling

When a liquid evaporates, it absorbs heat from the surroundings. This lowers the temperature of the surface.

Examples:

  • Sweating cools our body in summer.
  • Water cools in an earthen pot (matka).
  • Sprinkling water on the roof cools it.

Quick Quiz

  1. Which state of matter is highly compressible? (Ans: Gas)
  2. What is the boiling point of water? (Ans: 100°C)
  3. What is sublimation? Give two examples.

Home Experiments

  • Salt in water: See how particles mix.
  • Camphor sublimation: Watch it disappear directly into gas.
  • Steam condensation: Hold a plate over boiling water.

Summary Points

  • Matter has mass and volume.
  • Made of particles with spaces and motion.
  • Exists in 3 common states: Solid, Liquid, Gas.
  • Can change state by changing temperature or pressure.
  • Evaporation causes cooling.
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