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442 BC - Democritus formed the idea that all matter is composed of atoms.
1774 - Antoine Lavoisier proposed the Combustion Theory which was based on sound mass measurements.
1794 - Joseph Louis Proust published the Law of Definite Proportions which states that a compound is composed of exact proportions of elements by mass regardless of how the compound was created.
1803 - John Dalton created the first proposal of atomic theory.
1832 - Michael Faraday studied the splitting of molecules with electricity.
1897 - J.J. Thomson discovered the electron.
1898 - Marie and Pierre Curie discovered the radioactive elements polonium and radium.
1909 Ernest Rutherford developed the theory of the structure of an atom.
1909 - Through an experiment called the ‘oil drop experiment’, Robert Millikan discovered the charge and the mass of an electron.
1922 - The atomic model Neils Bohr created was made up of successive orbital shells of electrons.
1932 - James Chadwick discovered the neutron.
1930 - Erwin Schrodinger viewed electrons as continuous clouds and introduced wave mechanics as a mathematical model of the atom.
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