# Question #2b905

##### 1 Answer

The following timeline of the atomic model is highly condensed and omits many important contributions.

442 BC — Democritus/Leucippus — matter consists of indivisible particles.

1777 — Lavoisier — Law of Conservation of Mass

1803 — John Dalton — atomic theory of matter

1869 — Dmitri Mendeleev — Periodic Table and periodic law

1897 — J. J. Thomson — discovers electron

1898 — J. J. Thomson— plum pudding model of atom

1898 — Ernest Rutherford — discovers α and β rays

1900 — Frederick Soddy — discovers radioactive decay

1900 — Max Planck — quantum theory of energy

1905 — Albert Einstein — Quantization of light;

1909 — Ernest Rutherford — nuclear model of atom

1913 — Niels Bohr — orbital model of atom

1914 — H. G. J. Moseley — measures atomic numbers of nuclei

1923 — Louis de Broglie — discovers wave/particle duality

1926 — Erwin Schrödinger — develops Schrödinger equation

1930 — Paul Dirac — proposes anti-particles

1932 — Carl Anderson — discovers positron

1932 — James Chadwick — discovers neutron

1955 — Segrè/Chamberlain — discover antiproton

1955 on — many new discoveries about subatomic particles