Particulate Theory of Matter

Matter is defined as anything that has mass and takes up space.

The theory states that matter is made up of tiny particles and that these particles are in constant motion. The theory has several postulates that support it:

  • Particles of matter are held together by very strong electric forces;
  • There are empty spaces between the particles of matter that are very large compared to the particles themselves;
  • Each substance has unique particles that are different from the particles of other substances;
  • Temperature affects the speed of the particles. The higher the temperature the faster the speed of the particles.

This theory explains the homogeneous nature of pure substances, the physical changes that can occur (melting, evaporation, sublimation, etc.), and the physical properties of the substance under consideration (density, conductivity, etc.).


This is the movement of particles from a region of higher concentration to a region of lower concentration.

It is because of diffusion why you are able to smell your mother’s cooking in the living room long before you have reached the kitchen. It is because of diffusion why you are able to see water turn red when red food colouring is added to the glass. As long as there is movement of particles from an area of higher concentration to an area of lower concentration, diffusion has occurred.

How does diffusion affect us with regards to this theory? Look at the experiment below.

Experiment 1

A student is given potassium manganate crystals and a beaker of water. The student places the crystals in the beaker of water and let’s it sit on the work bench. After a while, the student began to notice that the crystals dissolved in the water. The beaker of water which was colourless was now a deep shade of purple as the potassium manganate dissolved. The student noted that the change in colour took about an forty five minutes.

The teacher told the students to take out their Bunsen burners and fill a fresh beaker with water. The students were given new crystals. The students lit the Bunsen burners and placed the new beaker with water on the burner. The fresh crystals were then added. The student noticed that the same thing that happened above happened here. The only difference was that it took less than 20 minutes, for the purple colour to pervade the beaker.

The take home message from the narration of the experiment above is that diffusion supports the particulate theory of matter and its supporting postulates.


This is the movement of water from an area of higher concentration to an area of lower concentration across a semi-permeable membrane. The key thing to remember when dealing with osmosis is that a semi-permeable membrane has to be involved. If there is no membrane then osmosis has not occurred and another method of movement of particles needs to be examined. To see how osmosis supports the theory read the second experiment narration below.

Experiment 2

 In the next chemistry class the students were given a petri dish containing a very salty solution and a piece of potato. They were told to place the potato in the high salt solution and leave it there until the next chemistry lab. On the return of the students to lab they noticed that the potato was shriveled, shrunken and dried out.

The students were then given new petri dishes which contained fresh water. they were told to put the potato piece in the fresh water and leave it until the next lab. On their return to the next lab session, the potato was restored to its former starchy glory.

If you have any questions or comments please do not hesitate to comment below!



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