History of Atomic Theory

John Dalton

Feb 3, 1803

John Dalton recognised the existance of atoms of elements and that compounds formed from the union of these elements John Dalton also discovered colour blindness, which he suffered from. He determined that five percent of the male population and less than one-tenth percent of the female population was color blind.

J.J Thomson

Sep 12, 1897

J.J Thomson identified the negativley charged electron in the cathode ray tube in 1897. He concluded that the electron was a component of all matter and calculated the charge to mass ratio for the electron. e/m = -1.76 x 108 coulombs/g

Marie Curie

Jul 22, 1903

Marie Curie along with her husband, Pierre, discovered the elements polonium and radium. They were both awarded the Nobel Prize for Physics in 1903, and she received another one for Chemistry in 1911.

Ernest Rutherford

Mar 8, 1911

Ernest Rutherford proposed the nuclear atom as the result of the gold-foil experiment in 1911. Rutherford suggested that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. Also in 1920, Rutherford proposed the existence of the third atomic particle the neutron.

Henry Mosely

May 30, 1913

Henry Mosely developed the X-ray spectra to study atomic structure. Moseley's discoveries resulted in a more accurate positioning of the elements on the periodic table.

Francis Aston

Oct 13, 1920

Francis invented the mass spectograph in 1920. He was the first person to observe isotopes. Aston's work led Rutherford to predict the existance of neutron.

Niels Bohr

Jul 23, 1922

Niels Bohr was one of the leading scientists of modern physics. He was best known for his substantial contributions to quantum theory and his Nobel Prize-winning research on the structure of atoms.

Erwin Schrodinger

Sep 19, 1926

In 1926 Erwin Schrodinger created a powerful model of a wave equation that accurately gave the energy levels of atoms. This atomic model is known as the quantum mechanical model of the atom.

James Chadwick

Jan 2, 1932

James Chadwick discovered the neutron in 1932. This discovery led to the finding of fission and later the atomic bomb.Chadwock also worked with Rutherford on the neutron theory.

Murray Gell Mann

Nov 30, 1969

Murray Gell Mann showed scientists that quarks make up protons and neutrons. He found the quark is a fast moving point of energy and every proton and neutron contains three. There are two types of quarks within the neutron and proton, up quarks and down quarks.