Matter 

Synposis 

• Matter is the substance which occupies space and has mass. 
• The three states of matter are 

1. solid, 2. liquid 3. gas. 

• Matter is composed of large number of molecules. 
• A molecule is the smallest particle which can exist freely in nature by itself and it retains the properties of the substance. 
• All molecules of a substance are identical, but the molecules of different substanes are different. 
• A molecule is very small in size (10-10 m). 
• The molecules are separated from each other with spaces called inter-molecular spacing. 
• The molecules in a substance are held together by the forces acting between the molecules which are called the inter-molecular forces. 
• The force of attraction between the molecules of the same sub¬stance is called the force of cohesion, while the force of attraction between the molecules of two different substances is called the force of adhesion. 
• The forces of cohesion and adhesion are effective only when the separation between the molecules is 10-9 m. When the separation becomes more, they vanish. 
• The molecules in a substance are not at rest, but they are con¬stantly in motion. 
• In a solid, the molecules are rigid, the inter-molecular spacing is least, the inter- molecular forces are strongest and the molecules remain in their fixed positions. They vibrate to and fro about their mean positions, but they do not leave their positions, so a solid has a definite shape and a definite volume. 
• In a liquid, the molecules are not rigid, the inter-molecular spacing is more than that in solids, the inter-molecular forces are weak and the molecules are free to move within the boundary of the liquid, so the liquid has a definite volume, but it does not have a definite shape. 
• In gases, the molecules are not rigid, the inter-molecular spacing is more than that in solids and liquids, the inter-molecular forces are weakest and the molecules are free to move anywhere in space. So the gas has neither a definite volume nor a definite shape.