Matters in our surroundings Class 9 Notes

Matter in our surroundings Class 9 Notes

Matter in our Surroundings

Matter is defined as anything that occupies space and has mass and is felt by our senses. 


We can see around us. Everywhere we can see an example of matters . The water , air, ice cubes, iron, copper, etc are examples of matters. We can categorise the matter in three different ways called the state of matter.

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Characteristics of matters

  • These Matters are Made of tiny particles. 

  • Vacant spaces exist between particles. 

  • These Particles are in a continuous motion. 

  • The Particles of matter are held together by the forces of attraction. 

States of Matter 

Basis of Classification

  • Based upon particle arrangement 

  •  Based upon energy of particles 

  •  Based upon distance between particles 

There are three basic states of matter

1. Solid 

2. Liquid 

3. Gas 

Along with above three state there are two more States of Matter to be read on higher classes

  1. Plasma 

  2. Bose-Einstein condensate 


  • Solids are those matters which have a Fixed mass, volume and shape. 

  • In a solid material the Inter-particle distances are least. 

  • These are generally Incompressible. 

  • They have high density and they do not diffuse with each other. 

  • The Inter particle forces of attraction are strongest in solids. 

  • The Constituent particles in solids are very closely packed. 


  • Liquids have not a fixed shape but fixed volume and mass. 

  • In the liquid state of matter the Inter particle distances are larger than solid. 

  • These are Almost incompressible. 

  • The Density of liquid particles is lower than solids and can diffuse. 

  • The Inter particle forces of attraction in liquids are weaker than solids . 

  • Also, the Constituent particles are less closely packed as compared to solids.


  • The gases are the form of matters which have Neither fixed shape nor the fixed volume. 

  • The  Inter particle distances between Particles are largest. 

  • Gases are Highly compressible and can be filled in small spaces.

  • The  Density of gases are least and diffuse. 

  • Inter particle forces of attraction between Particles are weakest. 

  • The Constituent particles of gases are free to move about each other. 

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Interchange in states of matter

As we know that Water can exist in three states of matter –

i.e. Solid (ice), Liquid (as the familiar water) and Gas (the water vapour).

Sublimation : Sublimation is the process of changing of solid directly into vapours while heating and

vapours into solid while cooling. 

Ex. Ammonium chloride, camphor & iodine. 

Effect of change in temperature

The effect of temperature depends on the nature of the solid and the conditions required in bringing the change. 

  • When we increase the temperature of a solid, the kinetic energy of the particles increases which overcomes the forces of attraction between the particles,  as a result the solid melts and is converted to a liquid. 

  • The temperature at which a solid started melting to become a liquid at the atmospheric pressure is called the melting point of the solid.

  • The melting point of ice is known and it is  equal to 273.16K or 0°C

  • The process of melting of substance, i.e. change of solid state into liquid state is also known as fusion. 

Effect of Change of Pressure

The process of Increasing or decreasing the pressure of matter, can change the state of matter. 

  • If we apply pressure to a gas and reduce its temperature, then it can liquefy gases. 

  • Solid carbon dioxide (CO2) is stored under high pressure, because it gets converted directly to gaseous state on decrease of pressure to 1 atmosphere without coming into a liquid state. The Solid carbon dioxide is also known as dry ice. 

Latent Heat 

The hidden heat energy in a matter  which breaks the force of attraction between the molecules during change of state is known as Latent Heat.

It is defined as the heat energy, required to change the state of 1 kg substance at constant temperature.

Latent heat of Fusion : Latent heat of Fusion is defined as the heat energy required to change 1kg of solid into liquid at its melting point.

Latent heat of Evaporation : Latent heat of Evaporation is defined as the Heat energy required to change 1kg of liquid to gas at atmospheric pressure at its boiling point.

Hence, we can say that pressure and temperature can change the state of a 

substance, whether state will be solid, liquid or gas. 

 Evaporation and Boiling

The Particles of matter are always in a state of motion and hence have some kinetic energy with it.  At a given temperature in any gas, liquid or solid, these  particles have a certain amount of kinetic energy. 

In the case of liquids, the particles at the surface have higher  energy as compared to the inner particles and hence they are  able to break away from the forces of attraction of other particles and get converted into vapour. This phenomenon of change of a liquid into vapours below its boiling point is known as evaporation. 

Factors Affecting Evaporation

  • The rate of evaporation depends upon the surface area of the matter and increases with an increase of surface area.

  • It also depends upon the temperature and increases with the increase of temperature. 

  • Humidity : Humidity is the amount of water vapour present in air. The rate of Evaporation depends on humidity. The air around us can have a limited amount of water  vapour with it  at a given temperature. If the amount of water in air is high, then the rate of evaporation decreases. 

Evaporation causes cooling

The particles of liquid absorb energy from the surrounding to regain 

the energy lost during evaporation and hence it causes cooling.

Evaporation Vs Boiling

Boiling is a bulk phenomenon that occurs in the whole liquid. Particles from the bulk (whole) of the liquid changes from liquid state  into vapour state. 

Evaporation is a surface phenomenon in which Particles from the surface gain enough energy to overcome the forces of attraction between different particles of liquid  and hence break out from the liquid and change into the vapour state. 

Kelvin & Celsius Scale

Kelvin is the SI unit of temperature, 0°C = 273.16 K 

we take 0°C = 273 K. 

The SI unit of temperature is Kelvin. 

 The relation between Kelvin and Celsius scale is given by    

             K  =  °C  +  273.16

Kelvin scale of temperature has always positive sign and it is  regarded as the better scale than Celsius.

Atmospheric pressure 

The pressure of air in the atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure.

This unit is generally used to  measure the pressure exerted by a gas. 

The SI unit of pressure is Pascal (Pa) 

And, 1 atmosphere = 1.01 × 105 Pa. 

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Is Matter Around us Pure

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