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Atomic Theory Timeline

Check out this amazing Timeline on Atomic History!

442 BC
Philosopher Democritus thought that all matter is composed of indivisible elements.

1805
John Dalton proposed each chemical element consists of a single type of atoms that could not be destroyed. This marked the official beginning of the atomic theory.

1811
Amedeo Avogadro law made it possible to accurately estimate the atomic mass of an element. This also made a clear distinction between atoms and molecules.

1827
Robert Brown observed dust particles floating in water, moving randomly for no known reasons.

1897
J.J. Thomson discovered the electron. He believed atoms could be divided.

1904
J.J. Thomson released his Plum Pudding model of the atom.

1905
Albert Einstein postulated the Brownian motion was due to the movement of water molecules.

1908
Jean Perrin provided experimental confirmation for Einstein’s observations. Additionally, Perrin’ observations enabled him to estimate the size of water molecules and atoms as well as their quantity in a given value.

1909
Ernest Rutherford disproved the plum pudding model J.J. Thomson in and creates the Rutherford model which resembles a planetary model.

1913
Niels Bohr proposed the Bohr model. This model stated that electrons only orbit the nucleus, also according to his model, the electrons couldn’t spiral into the nucleus, but could bound between energy levels.

1913
Frederick Soddy described isotopes, atoms that contains different numbers of neutrons.

1926
Erwin Schrodinger described how electrons move in a waveform using Schrodinger’s equation.

1930
Paul Dirac proposed anti-particles.

1932
Carl Anderson discovered the anti-electron (positron).

1933
James Chadwick discovers the neutron completing the atomic model.

1938
Otto Hahn and his assistant Fritz Strassmann discovered nuclear fission of heavy elements.

1939
Lise Meitner theoretically explain Hahn’s and Strassmann’s discovery.

1941-1951
Glenn Seaborg synthesized 6 transuranium elements and changed the layout of the periodic table.

1945
The first combat atomic bomb is used in Japan launching the a nuclear era making the atoms famous around the world.

1954
At Obninsk, Russia the first nuclear power plant produced commercial electricity.

1955
Emilio Segre and Owen Chamberlain detected the anti-proton.

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