Atomic Theory History

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  • 460

    Democritus

    460 BC – ca. 370 BC Greece He stated the first atomic theory. His hypothesis on atoms is remarkably similar to modern science's understanding of atomic structure. Formulated an atomic theory for cosmos. http://en.wikipedia.org/wiki/Democritus
  • Period: 460 to

    Atomic Theory History

  • Isaac Newtown

    1704 England Isaac Newtown accepted atomism, but raised the question of creation as a result of pure chance which traditional atomic theory implied. He argued that light were composed of corpuscles, or particles, which much later led to the quantum properties of matter. http://galileo.phys.virginia.edu/classes/252/atoms/html

  • John Dalton

    1803 England All matter consists of tiny particles, atoms are indestructible and unchangeable and when elements react, their atoms combine in simple, whole-number ratios He was the first to prepare a table of atomic weights. He rationalised the various laws of chemical combination which were in existence at that time. http://www.rsc.org/chemsoc/timeline//pages/1803.html

  • G.J. Stoney

    1894 Ireland He estimated the number of molecules in a cubic millimetre of gas, at room temperature and pressure, from data obtained from the kinetic theory of gases. In 1891, he proposed the term 'electron' to describe the fundamental unit of electrical charge, and his contributions to research in this area laid the foundations for the eventual discovery of the particle by J.J. Thomson in 1897. http://en.wikipedia.org/wiki/George_Johnstone_Stoney

  • J.J. Thomson

    1897 Britain In 1906 Thomson demonstrated that hydrogen had only a single electron per atom. He is credited for the discovery of the electron and of isotopes. http://en.wikipedia.org/wiki/J.J._Thomson

  • Max Planck

    1900 Germany This theory stated that radiant energy can only be emitted or absorbed in discrete quantities, like small packages. He gave the name quantum to the smallest quantity of energy than can be emitted in the form of electromagnetic radiation. http://en.wikipedia.org/wiki/Max_Planck

  • Hantaro Nagaoka

    1903 Japan Nagaoka developed an early, incorrect "planetary model" of the atom. The model was based around an analogy to the explanation of the stability of the Saturn rings (the rings are stable because the planet they orbit is very, very massive). First to present a Saturian atomic model close to the presently accepted model. The model described atoms as electropositive balls that had electrons scattered in them, like the raisins in raisin bread. http://en.wikipedia.org/wiki/Hantaro_Nagaoka

  • Robert Andrews Milikan

    1909 America Determined the unit charge of the electron with his oil drop experiment at the university of Chicago thus allowing for the calculation of the mass of the electron and the positively charged atom. Discovered the weight of an electron is 1836 times smaller. http://en.wikipedia.org/wiki/Robert_Andrews_Millikan

  • E. Rutherford

    1911 New Zealand Proposed the nuclear atom as a result of the gold-foil experiment. In early work he discovered the concept of radioactive half life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation. http://en.wikipedia.org/wiki/Ernest_Rutherford

  • H.G.J. Mosely

    1914 England Discovered that the energy of x-rays emitted by the elements increased in a linear fashion with each successive element in the periodic table. The justification from physical laws of the previous empirical and chemical concept of the atomic number. http://en.wikipedia.org/wiki/Henry_Moseley

  • Neils Bohr

    1922 Denmark Proposed that the outer orbit of an atom could hold more electrons than the inner orbit. Bohr’s atomic model introduced some quantum mechanics aspects to the atomic model, and, more importantly, it provided a theoretical frame for Ruberg’s formula, which had been observed only empirically. http://en.wikipedia.org/wiki/Niels_Bohr

  • James Chadwick

    1932 England Used alpha particles to discover a neutral atom particle with a mass close to a proton. Discovered the electron. He was a collaborator of Rutherford’s. The discovery of the neutron lead directly to the discovery of fission and ultimately to the atomic bomb. http://en.wikipedia.org/wiki/James_Chadwick