three states of matter

melting and freezing take place at the melting point

boiling and condensing take place at the boiling point 

the three states of matter can be represented by a simple model.in this , particles are represented by small solid spheres .

can help to explain changes of state using the movement of particles and the average distance between them .

changing from a solid to a liquid 

changing from a liquid to a gas 

changing from a liquid to a solid 

changing from a gas to a liquid 

energy is needed to change from solid to liquid (melting) and from liquid to gas (boiling)