Particulate nature of matter
Matter is made up of moving particles ATOMS IONS MOLECULES
kinetic theorychanges of state
3 states of matterSOLID LIQUID GAS
Diffusion is an evidence of moving particles
A word on diffusion:Particles move past agains each other and occupy total avaliable space.It does not occur in solids.In liquids it's much more slowly than in gases, because of slow movement of particles.Lighter molecules will move faster, so diffusion will take place faster as well.
Relative rates on diffusion:Lighter gases diffuse faster.