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Isaac Newton
Proposed a mechanical universe with small solid masses in motion. -
Period: to
Timespan of the Atomic Theory
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John Dalton
Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
Michael Faraday
Studied the effect of electricity on solutions, coined term "electrolysis" as a splitting of molecules with electricity, developed laws of electrolysis. Faraday himself was not a proponent of atomism -
J. Plucker
Built one of the first gas discharge tubes ("cathode ray tube"). -
Dmitri Mendeleeff
Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law. -
G.J. Stoney
Proposed that electricity was made of discrete negative particles he called "electrons". (Link to info on electrons) -
J.J. Thomson
Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 108 coulombs/gram. -
Rutherford
Studied radiations emitted from uranium and thorium and named them alpha and beta. And using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil. He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus. -
Soddy
Observed spontaneous disintegration of radioactive elements into variants he called "isotopes" or totally new elements, discovered "half-life", made initial calculations on energy released during decay. -
H.G.J. Moseley
Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote"The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Francis William Aston
Discovered the existence of isotopes through the use of a mass spectrograph. -
Niels Bohr
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons. -
de Broglie
Discovered that electrons had a dual nature-similar to both particles and waves. Particle/wave duality. Supported Einstein. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. -
Enrico Fermi
CitationsConducted the first controlled chain reaction releasing energy from the atoms nucleus.
