Solid: The particles are pact together in a regular structure. The particles vibrate.

Liquid: The particles have no regular arrangement so they can flow but they are still quite closely pact together.

Gas: The particles have no regular arrangement and they are not bonded together. They move in random motion.

solid to liquid = melting
liquid to solid = freezing
gas to liquid = condensing
liquid to gas = evaporating
solid to gas = subliming

Diffusion
Diffusion is the movement of particles to fill the space they are in. This happens most rapidly with gases, slower with liquids and very slowly or not at all with solids.