Matter in Our Surroundings Class 9 Notes: CBSE 9th Science Chapter 1 Revision Notes, Download PDF Here

Matter in Our Surroundings Class 9 Notes: CBSE Class 9 Science revision notes for Chapter 1- Matter in Our Surroundings are available here. These notes are entirely according to the latest CBSE syllabus of Class 9 Science. Check these chapter notes for a quick revision of the chapter. 

CBSE Class 9 Science Matter in Our Surroundings Notes

• Everything in this universe is made up of material which scientists have named “matter”. They have both mass and volume.

• Since early times, human beings have needed to use the idea that matter is made up of trying to understand their surroundings. of particles. What was there in the spoon, salt Early Indian philosophers classified matter in or sugar, has now spread throughout water. the form of five basic elements — the “Panch. I.e., air, earth, fire, sky and water.
• According to them everything, living or nonliving, was made up of these five basic elements. 
• Modern day scientists have evolved two types of classification of matter based on their physical properties and chemical nature.

Physical Nature of Matter

• Matter is made up of particles. The particles of matter are very small –
• Characteristics of Particles of Matter:
  • Particles of matter have space between them. The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.
  • Particles of matter are continuously moving. They possess what we call the kinetic energy. As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases.

• • Particles of matter attract each other. Particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another. The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases. 

• States of Matter: Matter around us exists in three different states– solid, liquid and gas. These states of matter arise due to the variation in the characteristics of the particles of matter.

• • Solid State: These have a definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility. Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.

• • Liquid State: Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid.
    • Solids, liquids and gases can diffuse into liquids. The rate of diffusion of liquids is higher than that of solids. This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state.

• • Gaseous State: Gases are highly compressible as compared to solids and liquids. Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.
    • In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

Can Matter Change its State? 

The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure. 

Effect of Change of Temperature

• On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. 
• The melting point of a solid is an indication of the strength of the force of attraction between its particles.

• Fusion: The process of melting, that is, change of solid state into liquid state is also known as fusion. The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at 0oC (273 K) have more energy as compared to particles in ice at the same temperature.
• When we supply heat energy to water, particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature the liquid starts changing into gas. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. 
• Sublimation: A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition.
• Deposition: Deposition is the change of gaseous state directly to solid state without going through liquid state. 

Evaporation 

• Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.
• The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.
• Evaporation causes cooling.
• Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
• Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point. 

Some Measurable Quantities and their Units 

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