Atomic Theory

By zozo
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    Democritus (Greek)

    Democritus (Greek)
    Put forward the idea that matter could be divided into smaller particles, which he called atoms.
  • Isaac Newton (British)

    Isaac Newton (British)
    Proposed a mechanical universe with small solid masses in motion. This brought forward the model of the structure of atoms, though the idea was not known until 1912.
  • John Dalton (British)

    John Dalton (British)
    Suggested that matter is made of indivisible particles or atoms and that each chemical element consisted is made up of its own characteristic atoms. He also stated that compounds contain atoms of different elements joined in a simple ratio.
  • G.J. Stoney (Irish)

    G.J. Stoney (Irish)
    Proposed that electricity was made of discrete negative particles which he called ‘electrons.’
  • J.J. Thomson (British)

    J.J. Thomson (British)
    Discovered the electron and showed that electrons are negatively charged particles. He proposed that the atom has electrons embedded in a nucleus of positive charge.
  • Max Planck (German)

    Max Planck (German)
    Explained that energy could only be transferred in very precise and small amounts, of which he called quanta. This contributes to the understanding of atoms as it comes to explain that action of an electron bound into an atom or molecule is quantized.
  • Nagaoka (Japanese)

    Nagaoka (Japanese)
    Postulated a ‘Saturnian’ model of the atom with flat rings of electrons revolving around a positively charged particle. He predicted that they were bound by electrostatic forces.
  • R. Milikan (American)

    R. Milikan (American)
    Determined charge and mass of an electron.
  • Ernest Rutherford (British)

    Ernest Rutherford (British)
    Identified positively charged particles (protons), which gave the atom most of its mass. He proposed that had a small positive nucleus that was surrounded by an equal number of orbiting electrons.
  • Niels Bohr (Danish)

    Niels Bohr (Danish)
    Proposed an atomic model where electrons travel around the nucleus in fixed orbits and each orbital shell has a definite amount of electrons.
  • H.G.J. Mosely (British)

    H.G.J. Mosely (British)
    Determined the charges on the nuclei of most atoms, that is, 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.
  • James Chadwick (British)

    James Chadwick (British)
    Discovered the neutron and found it to be of similar mass to the proton.