Chem Atomic Theory Timeline

John Dalton

1808

1766-1844. He showed that common substances broke down into the same element and proportions. Each is a different size and matter. Based on all his observations, Dalton proposed his model of an atom. It is often referred to as the billiard ball model.

J.J. Thomson

1904

1856-1940. Discovered electrons, about the negativity and positivity. Won a Nobel prize in 1940 for discovery. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup."

Ernest Rutherford

1911

Father of the nuclear age. Had a gold foil experiment. The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun. And was a student of J.J. Thomson.

Niels Bohr

1913

Discovered that the electrons orbit the nucleases at a fixed energy and distances. His model took center stage but they found some complications to it. In this model, the electrons travel around the nucleus of an atom in distinct circular orbits, or shells. The model is also referred to as the planetary model of an atom.

James Chadwick

1932

He made a discovery in the domain of nuclear science. James Chadwick's contribution to the atomic model was his discovery of the neutron. The neutron is a neutrally charged subatomic particle that is about the same mass as the proton. He proved that the existence of neutrons, elementary particles devoid of any electrical charge.