History of Atomic Structure

  • 460

    Democritus c. 460

    Abdera, Thrace, Greece
    Formulated an atomic theory for the cosmos. His speculation on atoms gave an understanding of atomic structure. Many consider him as the ‘father of modern science.’
  • Newtown 1704

    Lincolnshire, England

    Proposed a mechanical universe with small solid masses in motion. He also suggested that atoms were held together by attractions that we now call forces. His work has enabled other scientists such as Dalton to develop the atomic theory.
  • Dalton 1803

    Cumberland, England
    Proposed an ‘atomic theory’ with spherical solid atoms based upon measurable properties of mass. His idea was later extended. He also printed the first published table of relative atomic weights.
  • G.J. Stoney

    Proposed that electricity was made of discrete negative particles he called electrons. He has introduced the term electron as the ‘fundamental unit quantity of electricity’ and now it is widely used.
  • J.J. Thomson

    Manchester, England
    Used a CRT to experimentally determine the charge to mass ratio of an electron. He has been credited for the discovery of the electron and of isotopes.
  • Planck 1900

    Used the idea of quanta (discrete units of energy) to explain hot glowing matter. He was the founder of the quantum theory and is one of the most important physicist of the twentieth century.
  • Nagaoka 1903


    Postulated a ‘Saturnian’ model of the atom with flat rings of electrons revolving around a positively charged particle. He was a pioneer of Japanese physics. He work was later extended and pursued by Rutherford.
  • Millikan 1909

    Illinois, USA

    Worked on an oil drop experiment that determined the charge and the mass of an electron. His experiment was accurate and was used by other scientists.
  • E. Rutherford 1911

    Brightwater, New Zealand

    Published his atomic theory describing the atom as having a central positive nucleus surrounded by negative orbiting electrons . This helped develop the atomic theory as we know it today. He was known as the ‘father of nuclear physics.’
  • H.G.J. Moseley 1914

    Used x-ray tubes to determine the charges on the nuclei of most atoms. He showed that atomic numbers had a strong physical basis.
  • Bohr 1922

    Copenhagen, Denmark
    Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His work made foundational contributions to understanding atomic structure and quantum mechanics.
  • James Chadwick 1932

    Cheshire, England

    Used alpha particles to discover a neutral atomic particle with a mass close to the proton. Thus was discovered the neutron. He discovered the neutron which allowed for further development to occur into atomic structure.