The idea of the atom is not a modern one. The early Greeks believed that all matter was composed of atoms. According to them if something was divided continuously till it could not be divided further, the last bit was an atom. In fact that the word atom comes from the Greek language which means “unsplitable” or “undivisible”. The Greeks however, spoke of the atom in a philosophical way and not as a scientific idea.

In 1803 John Dalton proposed the theory of atoms. Dalton was an English chemist and mathematician, who was the first man to develop a scientific atomic theory of atoms. He considered the atom to be the smallest part of matter. Dalton carefully weighed different samples of gases, solids and liquids and discovered that they weighed different. He realized that all matter was made up of extremely tiny particles, which he too called atoms.

When Dalton stated that the atoms of different elements have different properties and different weights, he started the scientific knowledge of the atom. Daltons work on the nature of matter provided the basis for modern atomic theories. He devised a system of classification by atomic weight. His work on gases led him to the law of partial pressure of gases, which came to be known a as Daltons law.

About a hundred years later, Ernest Rutherford a New Zealand physicist, tried to explain what the atom was and how it functioned. He developed the atomic theory, which closely resembled that of the solar system. He recognized that nuclear nature of the atom. According to him there was a heavy nucleus in the centre, with a positive charge of electricity. This was surrounded by negatively charged electrons.

The Danish physicist, Niels Bohr worked with Rutherford in Manchester, England. Later on his own he worked out the new atomic structure which is known as the Bohr model. He received the Nobel Prize in 1922 for physics. During World War II he escaped from the Nazis and fled to USA. There he took part in the work on the atom bomb.

Today scientists have proved that the atom is not the smallest particle of an element. It is made up of still smaller particles. That was the work of another great scientist.