Dalton’s atomic theory

John Dalton was an English school teacher. In 1808, he put forth his theory. According to his theory, all matter, solid, liquid, gas or element, compound, mixture is composed of atoms. The postulates of Dalton’s theory are :

1. Matter is made up of atoms which are its smallest indivisible particles.

2. Atoms of a particular element are alike but different from atoms of another element.

3. Atoms are indestructible or indivisible.

4. Atoms of every element have a characteristic mass.

5. Atoms combine to form compound –atoms called molecules.

6. A molecule is the smallest unit of a compound or element which exists in free-state.

Dalton’s theory could explain the existing laws at that time and it proposed the concept of atomic mass. However, the assumption that ‘atoms are indestructible or indivisible’ is not true.