Important Points and Formulas: Matter in Our Surroundings | Science Class 9 PDF Download

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MATTER IN OUR SURROUNDINGS 
 
 
 Matter 
Everything in this universe is made up of matter. Matter is defined as anything which occupies 
space, possesses mass and the presence of which can be felt by any one or more of our five 
senses, i.e., sight, touch, smell, hearing and taste. 
 States of Matter 
 
Matter around us exists in three states, i.e., solid, liquid and gas. These three states differ 
from one another due to the difference in the size of spaces in between the constituent 
particles, their forces of attraction and kinetic energies. 
 Differences in the characteristics of states of matter (solids, liquids & gases)  
S. No. Property Solid Liquid Gas 
1. Packing The particles are 
most closely packed. 
The particles are less 
closely packed than 
solids. 
Particles are at 
sufficient distances 
from each other. 
2. Shape Solids have definite 
shape. 
Liquids do not have 
definite shape. They 
assume the shape of 
container. 
Gases do not have a 
definite shape. They 
assume the shape of 
container.  
3. Volume Solids have definite 
volume. 
Liquids have definite 
volume. 
Gases do not have 
definite volume. They 
assume the volume 
of container.  
4. Density Solids have high 
density. 
Liquids have less 
density than solids but 
more than gases. 
Gases have the least 
density. 
5. Diffusion Solids have no 
tendency to diffuse. 
Liquids have a 
tendency to diffuse 
slowly. 
Gases diffuse 
rapidly. 
6. Rigidity Rigid. Fluid. Fluid. 
7. Compressibility Negligible. Very low. High. 
8. Inter-molecular 
forces of 
attraction 
Maximum. Less than solids. Negligible. 
9. Kinetic energy 
of molecules 
Least. More than solids. Very high. 
 MATTER 
Solid State 
(Have definite shape and 
definite volume) 
e.g. Chair, Stone etc. 
Liquid State 
(Have definite shape but 
no definite volume) 
e.g. Water, Milk etc. 
Gaseous State 
(Have no definite shape 
and no definite volume) 
e.g. Air, Oxygen etc. 
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1 
 
MATTER IN OUR SURROUNDINGS 
 
 
 Matter 
Everything in this universe is made up of matter. Matter is defined as anything which occupies 
space, possesses mass and the presence of which can be felt by any one or more of our five 
senses, i.e., sight, touch, smell, hearing and taste. 
 States of Matter 
 
Matter around us exists in three states, i.e., solid, liquid and gas. These three states differ 
from one another due to the difference in the size of spaces in between the constituent 
particles, their forces of attraction and kinetic energies. 
 Differences in the characteristics of states of matter (solids, liquids & gases)  
S. No. Property Solid Liquid Gas 
1. Packing The particles are 
most closely packed. 
The particles are less 
closely packed than 
solids. 
Particles are at 
sufficient distances 
from each other. 
2. Shape Solids have definite 
shape. 
Liquids do not have 
definite shape. They 
assume the shape of 
container. 
Gases do not have a 
definite shape. They 
assume the shape of 
container.  
3. Volume Solids have definite 
volume. 
Liquids have definite 
volume. 
Gases do not have 
definite volume. They 
assume the volume 
of container.  
4. Density Solids have high 
density. 
Liquids have less 
density than solids but 
more than gases. 
Gases have the least 
density. 
5. Diffusion Solids have no 
tendency to diffuse. 
Liquids have a 
tendency to diffuse 
slowly. 
Gases diffuse 
rapidly. 
6. Rigidity Rigid. Fluid. Fluid. 
7. Compressibility Negligible. Very low. High. 
8. Inter-molecular 
forces of 
attraction 
Maximum. Less than solids. Negligible. 
9. Kinetic energy 
of molecules 
Least. More than solids. Very high. 
 MATTER 
Solid State 
(Have definite shape and 
definite volume) 
e.g. Chair, Stone etc. 
Liquid State 
(Have definite shape but 
no definite volume) 
e.g. Water, Milk etc. 
Gaseous State 
(Have no definite shape 
and no definite volume) 
e.g. Air, Oxygen etc. 
 
 
 
• Besides solids, liquids and gases, there are two other states of matter, i.e., plasma 
and Bose-Einstein Condensate (BEC). 
 Inter Conversion of States of Matter 
• The states of matter are inter-convertible. This inter-conversion can be carried out 
either by changing temperature or pressure or both. For example, ice (solid) on heating 
becomes liquid water, which upon further heating gets converted into steam (gas). Similarly, 
a gas such as LPG can be liquefied on applying pressure. Likewise CO2 gas can be converted 
into dry ice (solid) by cooling under pressure. 
 
• The temperature at which a substance melts to form a liquid at atmospheric pressure 
is called its melting point. Once the melting process starts, the temperature remains the same 
till the entire solid melts even though we continue to supply the heat. This heat is actually used 
up in changing the state from solid to liquid by overcoming the forces of attraction between 
the particles. Since the heat supplied is absorbed by the particles without showing any rise in 
temperature, this is called latent heat of fusion. It is the amount of heat energy required to 
change 1 kg of a solid into liquid at atmospheric pressure at its melting point. The latent heat 
of fusion of ice is              3.347 × 10
5
 J/kg or 80 kcal/kg. 
• The temperature at which a liquid boils at the atmospheric pressure is called its boiling 
point. Once the boiling process starts, the temperature remains the same till the entire liquid 
changes into the gaseous state even though heat is continuously being supplied. Actually this 
heat energy is used up in changing the state from liquid to gaseous by overcoming the forces 
of attraction between the particles. Since this heat is absorbed without showing any rise in 
temperature, therefore, it is called latent heat of vaporization. It is defined, as the heat 
energy required in changing 1 kg of a liquid to the gaseous state at atmospheric pressure at 
its boiling point. The latent heat of vaporisation of water is 22.59 × 10
5
 J/kg or 540 kcal/kg.  
• Sublimation is the change of solid state directly into gaseous state without passing 
through the intervening liquid state, and vice-versa. The process of sublimation is used to 
purify volatile substances such as naphthalene, ammonium chloride, camphor, etc. from non-
volatile impurities. 
• Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into 
vapour state. 
• Evaporation is a surface phenomenon and involves the conversion of a liquid into 
vapours at any temperature below its boiling point. During evaporation, some of the particles 
on the surface of the liquid, which have high kinetic energy overcome the forces of attraction 
by the neighbouring particles, leave the liquid surface and get converted into vapours. 
Solid Gas
Liquid
Fusion 
Solidification
Sublimation
Sublimation
Vaporisation
Condensation