Atomic History

Democritus

442 BCE

Democritus never really "experimented." He believed everything was made up of atoms. He was one of the first people to consider that everything consisted of atoms.

John Dalton

Oct 21, 1803

Dalton published a table of relative atomic weights in 1803. This table had 6 elements. He determined that the structure of compounds can be shown in whole number ratios.

J.J. Thomson

Apr 30, 1897

Thomson did experiments that showed cathode rays were not actually rays, but were negatively charged particles; electrons. He though that electrons were distributed randomly and made the plum pudding model.

Ernest Rutherford

Mar 20, 1911

Rutherford did the gold-foil experiment. He found that the nucleus is positively charged, small, and dense. He also developed the Rutherford model of the atom.

Niels Bohr

Mar 20, 1922

Bohr made the Bohr atomic model, which consists of a small, positively charged nucleus in the center, surrounded by circles of electrons. He discovered that outer layers could hold more electrons than inner layers.

Louis De Broglie

Mar 20, 1924

Louis De Broglie had a theory called the matter and wave particle duality theory, which set the basis of wave mechanics.

James Chadwick

Mar 20, 1932

Chadwick discovered that there was a particle lacking an electric charge. He also discovered that this neutron had about the same mass as a proton.