• Anything that occupies space and has weight is called matter.
• Matter exists in three states- solid, liquid and gas.

SOLIDS

• • They have definite shape and volume.
  • They are generally hard.
  • They cannot flow.
  • They cannot be compressed easily.
  • They do not diffuse in the air.
  • Examples: rock, brick, table, chair etc.

LIQUIDS

• • They have a definite volume but no definite shape.
  • They are not hard.
  • They can flow from higher to a lower level.
  • They can be compressed slightly
  • They do not diffuse in the air.
  • Example: milk, water, oil etc.

GASES

• • They neither have a definite shape nor a definite volume.
  • They are not hard.
  • They can flow in all directions.
  • They can be compressed easily.
  • They diffuse in the air.
  • Example: oxygen, nitrogen etc.
• All matters are made up of very tiny particles called molecules.
• The force of attraction is greatest between the molecules in solids; therefore they are hard and cannot flow.
• In liquids, the force of attraction is less and hence they can be easily poured from one container to another.
• In gases, the force of attraction between the molecules is least and hence they can easily flow in any direction.
• Molecules are further made up of tiny particles called atoms.
• Every molecule has one or more atoms.
• Each molecule of Oxygen(O₂) contains two atoms of oxygen and each molecule of Nitrogen(N₂) also contains two atoms of nitrogen.
• When atoms of different kinds combine, compounds are formed.
• One molecule of water (H₂O) contains two atoms of Hydrogen and one atom of Oxygen.
• One molecule of Carbon Dioxide (CO₂) contains one atom of carbon and two atoms of Oxygen.
• Molecules have a certain amount of space between them and this space is known as intermolecular space.
• The solid that dissolves in a liquid is called a solute.
• The liquid in which a solute dissolves is called a solvent.
• When a solute dissolves in a solvent we get a solution.
• Heating or cooling causes a change in matter.
• When the change is only in the state of matter it is called a physical change.
• It is a temporary change:
  $water \underset{\mathrm{cooling}}{\stackrel{\mathrm{heating}}{\rightleftarrows }}water vapour$
• Heating of water changes it into water vapour and on cooling the water vapour it again changes into water. 
  $water \underset{\mathrm{heating}}{\overset{\mathrm{cooling}}{\rightleftharpoons }} ice$
• $Solid Wax \underset{\mathrm{cooling}}{\overset{\mathrm{heating}}{\rightleftharpoons }} Liquid Wax$
• The three forms of water are liquid water, water vapour (gas), and ice (solid).
• In some cases, heating or cooling results in a chemical change.
• When a piece of paper is burnt it changes into ash.
• A chemical change is a permanent change.