discovery of the atom

Democritus

400

Democritus introduces the philosophical concept of the atom in the universe. This begins the atomic theory - a theory of the nature of matter, which states that all matter is made up of atoms.

Dalton

Oct 21, 1803

Dalton proposes an atomic theory with spherical solid atoms, based upon measurable properties of mass. This atomic theory of Dalton explores the features of the atom its shape and state as well as the idea of atomic mass.

Thomson

Oct 21, 1897

J.J Thomson's 'Plum Pudding' model proposed before the discovery of the atomic nucleus. In 1897, J.J Thomson uses a Cathode Ray Tube to determine the ratio of mass to electrical charge of an electron. Thomson's experiment provides more thorough understanding of the structure of an electron and its properties.

Millikan

Oct 21, 1909

Millikan performs an oil drop experiment. This experiment determines the exact charge and mass of an electron. The charge of the electron that Millikan experiments on proves that all electrons have negative charges.

Rutherford

Oct 21, 1911

in rutherfords experement atoms in a very thin piece of gold foil are probed with alpha particles . This experiment establishes the nucleus as being very dense, very small and positively charged. From his observations Rutherford assumes that electrons are located outside the nucleus. This experiment introduces the nucleus and its properties, and shed more light on the contents of the atom.