In 1803, John Dalton, an English school teacher, proposed the Atomic theory of matter based on his experimental observations. The main postulates of Dalton’s atomic theory are as follows.

1. All matter is made up of extremely small particles called atoms.

2. Atoms of the same elements are alike but differ from atoms of other elements.

3. Atoms are indivisible.


4. Each atom has a definite weight.

5. Atoms of more than one element combine to form molecules.

Although Dalton’s theory failed to explain certain things, it is the cornerstone of modern chemistry. It had a profound influence on scientific thought. It underwent expansion, clarification and modification in an attempt to explain two things:

  • Divisibility of an atom, and
  • Existence of positive and negative charges.

Later on, scientists like Thomson, Rutherford and Bohr put forward their views and the discovery of electrons, protons and neutrons, provided evidence that disproved that the atom is indivisible.