Class 9 CBSE Science Chaper-1 Notes


Today we will discuss about Class 9 CBSE Science chapter 1 Notes Matter in our surroundings.

States of matter:-

  • Matter can be classified as solid ,liquid and gas.
Shape and volumeFixed shape and volumeNo fixed shape but has volumeNeither definite shape nor volume
CompressibilityDifficultNearly difficultEasy
EnergyLowestMedium Highest
Arrangement of moleculesRegular and closely arrangedRandom and sparsely arrangedRandom and sparsely arranged
FluidityCannot flowFlows from higher to lower levelFlows in all directions
MovementNegligibleDepends upon interparticle attractionFree constant and random
Interparticle space Very lessMore Large
Interparticle attractionMaximumMediumMinimum
Rate of diffusionNegligibleDepends on interparticle attractionMaximum
states of matter


  • The phenomenon by which molecules in liquid states undergo a substance spontaneous transition to gaseous phase at any temperature below its boiling point is called evaporation.
  • For example:-
    • The gradual drying of damp clothes is caused by the evaporation of water to water vapour.

Factors affecting evaporation:-

  • Temperature – The rate of evaporation increases with an increase in temperature.
  • Surface Area – The rate of evaporation increases with an increase in surface area.
  • Humidity – The rate of evaporation decreases with an increase in humidity.
  • Wind Speed – The rate of evaporation increases with an increase in wind speed.
  • Class 9 CBSE Science Chaper-1 Notes

Cooling due to evaporation:-

  • During evaporation, the particles of a liquid absorb energy from the surroundings o overcome the interparticle forces of attraction and undergo the phase change. The absorption of heat from the surrounding makes the surrounding cool.

Physical nature of matter:-

  • A physical property is that aspect of the matter that can be observed or measured without changing its nature or composition.
  • It is independent of the amount of matter present.
  • Physical properties includes appearance, color, odour ,density, texture, melting point, etc.

Characteristics of particles of matter:


-> Matter is anything that has mass and occupies space.

  • Everything that we can touch, smell, see, taste and also hear is matter.
  • It is made up of really tiny particles which cannot be seen is matter.
  • The particles of which the matter is comprised influence its state and properties.
  1. Particles of matter have spaces between them:-
  • This characteristics is one of the concept behind the solubility sugar in water, there is no rise in water level because the particles of sugar get into the interparticle spaces between the water particles.

2. Particles of matter are always in motion:-

  • Particles of the matter show continuous random movements due to the kinetic energy they possess.
  • A rise in temperature increases the kinetic energy of the particles, making them move more vigorously.


  • In every substance, there is an interparticle force of attraction acting between the particles. To break a substance we need to overcome this force. The strength of the force differs from one substance to another.


-> When the particles of matter intermix on their own with each other, the phenomenon is called diffusion. For example: spreading of ink in water.

  • During diffusion, the particles occupy the interparticle spaces.
  • The rate of diffusion increases with increase in the temperature, due to increase in kinetic energy of the particles.

Effect of change of temperature on state of matter:-

->On increasing temperature, the kinetic energy of the particles of the matter increase and they begin to vibrate with a higher energy. Therefore, the interparticle force of attraction between the particles reduces and particles get detached from their position and begin to move freely.

  • As a result, the state of matter begins to change.
  • Solids undergo a phase change to form liquids.
  • Similarly, liquids also undergo a phase change to form gases.
  • Class 9 CBSE Science Chaper-1 Notes

Melting point:-

-> The melting point of a solid is defined as the temperature at which solid melts to become liquid at the atmospheric pressure.

  • At melting point, these 2 phases, i.e. solid and liquids are in equilibrium, i.e. at this point both solid and liquid state simultaneously.

Boiling point:-

-> The boiling point of a liquid is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure.

Latent heat of fusion:-

-> It is the amount of heat energy that is required to change 1 kg. of a solid into liquid at atmospheric pressure at is melting point.


Class 9 CBSE Science Chaper-1 Notes

Class 9 CBSE Science Chaper-1 Notes
Class 9 CBSE Science Chaper-1 Notes

Latent heat of vaporisation:-

-> It is the amount of heat energy that is required to change 1 kg. of a liquid into gas at atmospheric pressure at its boiling point.


-> The transition of a substance directly from its solid phase to gaseous phase without changing into the liquid phase( or vice versa) is called sublimation.

Effect of change in pressure on state of matter:-

-> By applying pressure, the interparticle spaces between particles of matter decreases. Thus, by applying pressure and reducing temperature we can convert a solid to liquid and a liquid to gas.


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