Everything around us, including our bodies is made up of particles. These particles are so small it is impossible to pick them up and view with the naked eye.
To give you an idea of how small particles are, if you imagine a small raindrop, it contains over 1000 000 000 000 000 000 000 particles- amazing!
But if particles are so small that we cannot see them, what evidence is there for their existence?
Around 150 years ago a Scottish scientist called Robert Brown observed that pollen on water appeared to dance around as it was knocked around in all directions by the moving water particles (which were too small to see even under a microscope).
In the same way, if we examine smoke trapped in a glass box and shining light through it, we observe the tiny smoke specks dancing around in a random manner - continually on the move. This random motion of smoke and pollen is called Brownian Motion, after Robert Brown.
The diagram above shows the random motion of a single smoke speck as it is bombarded by air particles (which, again, are too small to see).
If you were to place a crystal of potassium manganate (VII) in a beaker of water, the water will eventually over time turn purple!
The reason behind this observation is:
If we imagine both the crystal and the water to be made up of particles, the bombardment of the water particles against the purple crystal will cause the gradual separation of the crystal particles. Eventually, the individual crystal particles spread throughout the water as they find space between the water's particles. If water and the crystal were not made up of particles, then mixing between the two would be impossible!
When a gas jar of colourless air is placed on top of a gas jar of red-brown bromine, the bromine vapour is seen to move upwards through the top gas jar, until a few minutes later both gas jars appear alike!
Both bromine and air are made up of fast gas particles at room temperature and pressure. When they come into contact with one another they collide and bounce off each other in all directions. Eventually they become evenly mixed. This is an example of diffusion.