Chapter 1: Particulate Theory of Matter (Shanice)

The Particle Theory of Matter:

1. Matter is made up of tiny particles (Atoms & Molecules)
2. Particles of Matter are in constant motion.
3. Particles of Matter are held together by very strong electric forces
4. There are empty spaces between the particles of matter that are very large compared to the particles themselves.
5. Each substance has unique particles that are different from the particles of other substances
6. Temperature affects the speed of the particles. The higher the temperature, the faster the speed of the particles.


Experiment :

Brownian motion can be demonstrated simply by releasing some smoke particles from burning cord into a small glass container and putting a cover plate to seal the smoke and air into the cell.

To investigate liquid molecular movement place some water with graphite particles suspended in it in the cell.

Now adjust the microscope slightly until you can see very bright specks. The particles of graphite (or smoke) scatter (reflect) the light shining on them and so appear as bright points of light darting about in a random or erratic motion. Note that the graphite (or smoke) particles are much larger than the water (or air) molecules. The particles can be seen by the light they scatter but the molecules themselves are too small to be seen.

The irregular movement of the visible particles of graphite (or smoke) is explained as being due to an uneven bombardment of the particles by the invisible molecules of water (or air). It is due to Brownian motion.

Brownian motion
We can conclude that lighter the particles faster the motion and denser the particles slower the motion.


Dissolving of Crystals in a Liquid due to Diffusion

Place some crystals of potassium permanganate at the bottom of a beaker. Slowly transfer water into the beaker with the help of a pipette. After sometime a dense purple solution is formed at the bottom and you will notice that it gradually spreads with the rest of water. After a few hours, it will be seen that the purple solution of a uniform concentration has formed throughout the solution.

This is because of the random motion of the potassium permanganate crystals in the water and by diffusion a homogeneous solution of potassium permanganate and water is formed.

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