John Dalton's Atomic Theory and other important scientists and their theories

John Dalton was an English school teacher who gave the first systematic idea of the structure of the atom. His statements are grouped together and are known as Dalton's atomic. He suggested that:

1. Atoms are small particles found in all matter. 
2. Atoms cannot be created nor be destroyed.
3. Atoms are indivisible.
4. Atoms of an element are identical.
5. Atom is the smallest unit of matter that takes part in a chemical reaction.

J.J. Thomson discovered the electron. Observations suggested that atoms contain negatively charged particles. He put forward the plum pudding theory of atoms. In this model of the atom, electrons are embedded in a sphere of positive charge.

In 1911, Ernest Rutherford suggested the following:

1. All atoms contain a small tiny central nucleus.
2. Most of the mass of an atom and all of the positive charge is being concentrated in the central nucleus. 

Neils Bohr suggested that:

1. Atoms revolve around the nucleus like planets around the Sun.
2. An electron can jump to a higher level by absorbing energy.
3. An electron fall to a lower level by giving out energy.

Rutherford-Bohr Model of an Atom

In 1932, James Chadwick discovered another subatomic particle i.e, neutrons which are present in the nucleus and have the same mass as the proton, but they have no charge.