Brownian Movement

Brownian Movement in chemistry is said to be the random zig-zag motion of a particle that is usually observed under high power ultra-microscope. This movement resembles the exact motion of pollen grains in water as explained by Robert Brown, hence, the name Brownian movement.

More significantly, Albert Einstein’s later explained the Brownian movement more clearly in his paper stating that the pollen was moved by water molecules. This discovery served as great evidence of the existence of atoms and molecules.

Understanding Brownian movement is crucial as it forms a base for the modern atomic theory. The kinetic theory of gases is also based on the Brownian motion model of particles. Additionally, the mathematical models describing Brownian motion are used in a variety of disciplines such as Maths, Physics, Chemistry, Economics, etc.

What is Brownian Movement?

Brownian movement also called Brownian motion is defined as the uncontrolled or erratic movement of particles in a fluid due to their constant collision with other fast-moving molecules.

Usually, the random movement of a particle is observed to be stronger in smaller sized particles, less viscous liquid and at a higher temperature. These are also some of the factors that affect the movement of particles in a fluid.

One of the most common examples of Brownian motion is diffusion. Cases, where pollutants are diffused in air or calcium diffused in bones can be considered examples of this effect.

Brownian Movement in Colloids

The Brownian motion effect is seen in all types of colloidal solutions. Besides, this phenomenon clearly explains the random motion of sol particles and indicates that these particles are not static. Nonetheless, the main reason for this type of motion in sol particles is due to unequal bombardment of the depressed phase particle leading to non-uniform movement in native due to the difference in the size of the particle.

Also Read: Colloids

Meanwhile, Brownian movement is not seen in true solution, where the system is homogeneous and the bombardment is uniform. However, in colloids the system is heterogeneous and the bombardments are non-uniform leading to the random measurement.

One of the key advantages of this effect is that it keeps sol particles in continuous motion, such that the particles do not settle at the bottom further preventing the coagulation of the lyophobic sols. This type of motion increases the stability of a sol.

Brownian motion is also observed in the plasma of cells in which the particles in the cell are also in random motion without making plasma in the cell dry.

Solved Questions

1. Why true solution does not follow Brownian movement?

Ans: True solution have smaller solute particles and homogenous these move uniform bombardment here then do not show Brownian movement.

2. How does the Brownian movement help in the stability of colloids?

Ans: The random movement of sol particles do not allow dispersed phase particles to settle at the bottom and thus prevents their coagulation.

3. Give any two examples of Brownian movement.


(i) Pollen grain in oil drop move.

(ii) Plasma particles in the cell.