Atomic Theory Timeline

  • 430

    Democritus - Greece

    Democritus introduced the concept that everything is made up of atoms. He formed the beginning of the atomis theory and set up the research and discoveries that would follow. Democritus developed a theory universe was made of empty space, and made up of an almost infinite number of indivisible, tiny particles, called atoms.
    He showed these atoms were different in form, position and arrangement.
  • Isaac Newton - England

    Isaac Newton proposed the laws of gravitation, and also the idea that we had a mechanical universe with small solid masses in motion. Newton believed creation was not by coincidence as the Ancient Greeks had believed, but the work of a Divine being (God). However his laws of gravitation (that every object in the universe attracts every other object with gravitational force) further developed the atomic theory.
  • John Dalton - England

    John Dalton proposed an ‘atomic theory’ that was based on measurable properties of mass. He proposed that atoms could not be made or destroyed. He also provided us with the weight of atoms which allowed us to distinguish one atom from another.
  • G.J. Stoney - Ireland

    Stoney proposed the concept of the electron. G.J Stoney also proposed that electricity was made of negative particles he called electrons. He introduced us to the basic concept of negative charge.
  • J.J. Thomson - England

    J.J. Thomson e discovered the electron and proved atoms had subatomic atoms. He also introduced the Plum Pudding model. J.J. Thomson allowed us to know about the existence of subatomic particles through cathode rays.
  • Planck - Germany

    Planck was the founder of the Quantum Theory, and created Planck’s Law of Black-body Radiation.
    The quantum theory changed and revolutionised the understanding of the atomic and subatomic processes
  • Hantaro Nagoka - Japan

    Nagoka created the Saturnian Model and introduced Spectroscopy.
    He created an inaccurate model of an atom based on the solar system analogy which helped us understand the structure of the atom.
  • R.A. Milikan - America

    Milikan measured the charge of the electron by using the oil drop experiment, and allowed us from then on to measure the charge to mass ratio of an electron.
  • Ernest Rutherford - British-New Zealand

    Rutherford proved that radioactivity involved the transmutation of one chemical element to another and differentiated and named alpha and beta radiation. He was also the first person to transmute one element into another. formulated the Rutherford model of the atom which is miniscule, positively charged nucleus orbited by electrons and established that the nucleus was very dense, small and positively charged. He assumed that electrons were located outside the nucleus
  • H.G.J. Moosley - England

    Moosley arranged the periodic table by their atomic numbers instead of atomic mass.He createf the Moseley Law that is an empirical law concerning the characteristic x-rays that are emitted by atoms. Using x-ray tubes he determined the charges on the nuclei of most atoms. He also wrote according to his arrangement of the periodic table, that the number of an element is equal to the number of protons in the nucleus.
  • Niels Bohr - Denmark

    Bohr helped with the understanding of the structure and properties of atoms. He also created the Bohr model of the atom’s shell which had atoms made up of successive orbital shells of electrons. Bohr suggested that the outer orbits could hold more electrons than the inner ones, and that these outer orbits determine the atom's chemical properties.
  • James Chadwick - England

    James Chadwick discovered the neutron by using alpha particles. He also discovered the mass was similar to that of a proton.