History Of The Atomic Theory

By jamiahlewis
  • 400 BCE

    Thinking About Matter

    Democritus’ atomic theory posited that all matter is made up small indestructible units he called atoms.

  • A Theory Maybe?

    Isaac Newton theorized a mechanical universe with small, solid masses in motion.

  • John Dalton and Atoms

    John Dalton proposed that elements consisted of atoms that were identical and had the same mass and that compounds were atoms from different elements combined together.

  • 1832

    Michael Faraday developed the two laws of electro-chemistry.

  • 1859

    J. Plucker built one of the first cathode-ray tubes.

  • 1869

    Dmitri Mendeleev created the periodic table.

  • 1873

    James Clerk Maxwell proposed the theory of electromagnetism and made the connection between light and electromagnetic waves.

  • 1874

    G.J. Stoney theorized that electricity was comprised of negative particles he called electrons.

  • 1879

    Sir William Crookes’ experiments with cathode-ray tubes led him to confirm the work of earlier scientists by definitively demonstrating that cathode-rays have a negative charge.

  • 1886

    E. Goldstein discovered canal rays, which have a positive charge equal to an electron.

  • 1895

    Wilhelm Roentgen discovered x-rays.

  • 1896

    Henri Becquerel discovered radiation by studying the effects of x-rays on photographic film.

  • 1897

    J.J. Thomson determined the charge to mass ratio of electrons.

  • 1898

    Rutherford discovered alpha, beta, and gamma rays in radiation.

  • 1898

    Marie Sklodowska Curie discovered radium and polonium and coined the term radioactivity after studying the decay process of uranium and thorium.

  • 1900

    Max Planck proposed the idea of quantization to explain how a hot, glowing object emitted light.

  • 1900

    Frederick Soddy came up with the term "isotope" to explain the unintentional breakdown of radioactive elements.

  • 1903

    Hantaro Nagaoka proposed an atomic model called the Saturnian Model to describe the structure of an atom.

  • 1904

    Richard Abegg found that inert gases have a “stable electron configuration.”

  • 1906

    Hans Geiger invented a device that could detect alpha particles.

  • 1914

    H.G.J. Moseley discovered that the number of protons in an element determines its atomic number.

  • 1919

    Francis William Aston used a mass spectrograph to identify 212 isotopes.

  • 1922

    Niels Bohr proposed an atomic structure theory that stated the outer orbit of an atom could hold more electrons than the inner orbit.

  • 1923

    Louis de Broglie proposed that electrons have a wave/particle duality.

  • 1929

    Cockcroft / Walton created the first nuclear reaction, producing alpha particles.

  • 1930

    Paul Dirac proposed the existence of anti-particles.

  • 1932

    James Chadwick discovered neutrons, particles whose mass was close to that of a proton.

  • 1938

    Lise Meitner, Hahn, Strassman discovered nuclear fission.

  • 1951

    Glenn Seaborg discovered eight transuranium elements.

  • 1942

    Enrico Fermi created the first man-made nuclear reactor.