History of the atomic model

John Dalton

1808

The atomism theory was discovered by John Dalton. The sum of the partial pressures that each individual gas applied while occupying the same space was the total pressure of a mixture of gases.

JJ Thompson

1897

The cathode ray tube studies of J.J. Thomson demonstrated that all atoms contain small, electron-like subatomic particles that are negatively charged. Thomson proposed the plum pudding model of the atom, which contained positively charged "soup" and negatively charged electrons inside.

Ernest Rutherford

1911

Rutherford came to the conclusion that the electrons must exist at the outermost regions of the atom while the bulk of the atom must be concentrated in a tiny positively charged nucleus.

Niels Bohr

1913

Since some physical quantities can only have discrete values according to quantum theory, Niels Bohr offered a hypothesis for the hydrogen atom in 1913. Only in its preset orbits do electrons travel around a nucleus; if they veer, the energy difference is released as radiation.

James Chadwick

1932

James Chadwick discovered a neutrally charged subatomic particle with roughly the same mass as the proton is the neutron. The atom's nucleus is made up of protons and neutrons. The neutron was found by Chadwick, who also determined its mass.