Atomic Theory Timeline

  • Isaac Newton's Theories

    Isaac Newton's Theories
    Newton proposed a mechanical universe with small solid masses in motion. He came up with the three laws of motion which described the universal gravitation, and we still use them today.
    His findings helped us in realising that we classify things according to our senses, but really, these are actually the types of atoms and the quality of voids (which determines the shape and existence of all things).
  • John Dalton's Investigations

    John Dalton's Investigations
    Dalton proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. He had the idea that each every element had a different type of atom that was determined by their masses, and that they cannot be created or destroyed. However, they can still combine to form more complex structures.
  • George Johnstone Stoney's Findings

    George Johnstone Stoney's Findings
    G.J. Stoney proposed that electricity was made of discrete negative particles he called electron. He introduced this term and concept as the "fundamental unit quantity of electricity" and this laid the foundations to J.J. Thomson's work about the particle theory in 1897.
  • J.J. Thomson's Experiments

    J.J. Thomson's Experiments
    In Britain, Sir Joseph John Thomson conducted an experiment using a CRT to determine the charge to mass ratio (e/m) of an electron = 1.759 x 108 coulombs/gram. He also
    studied “canal rays” and found they were associated with the proton H +, and was awarded the Nobel Prize in Physics 1906 "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases". His research showed that an atom was actually a jigsaw made of smaller parts.
  • Max Planck's Quantum Theory

    Max Planck's Quantum Theory
    Planck's Quantum Theory explained hot glowing matter using the idea of discrete units of energy. His research helped Bohr come up with an addition to Rutherford’s atomic model, and his equations were able to reflect the energy to temperature and frequency. Through all this, he was able to grasp an idea of the movement of electrons.
  • Nagaok's Saturnian Model

    Nagaok's Saturnian Model
    Nagaoka’s early “planetary model” was based around an analogy of the atom to the explanation of the stability of the Saturn rings. His prediction was that electrons revolved around the nucleus and bound by electrostatic forces (in analogy to the rings recolving around Saturn bound by gravitational forces) and that it had a very large nucleus (in analogy to the large planet).The model also demonstrated electrons revolving around a positively charged particle through the flat rings on the planet.
  • Millikan's Experiment

    Millikan's Experiment
    Robert Millikan conducted the oil drop experiment that determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. He established that the weight of an electron is 1836 times smaller than that of a hydrogen atom (atomic mass of 1) and all his figures were exact, thus contributing to the field of atomic theory in science.
  • E. Rutherford's establishments

    E. Rutherford's establishments
    Robert A. Millikan used alpha particles as atomic bullets and probed the atoms in a piece of thin (0.00006 cm) gold foil. From this, he assumed that electrons are located outside the nucleus and established certain characteristics of the nucleus such as it being very dense, small and positively charged. His model also showed the nucleus of an atom visually with protons, neutrons and electrons, and it is used as the cartographic symbol for a nuclear power plant.
  • H.G.J Moseley's Research

     H.G.J Moseley's Research
    Henry Gwyn-Jeffreys Moseleyused x-ray tubes in an experiment to determine the charges on the nuclei of most atoms. He wrote: "The atomic number of an element is equal to the number of protons in the nucleus" and this idea has been used ever since. Its most significant use would be in reorganising the periodic table based upon atomic number instead of atomic mass.
  • Niels Bohr's Discovery

    Niels Bohr's Discovery
    Bohr discovered that electrons had a dual nature-similar to both particles and waves, and this expanded on Rutherford’s atomic theory. He proposed that electrons travel only in certain orbits and that different electron shells have the capacity to hold different numbers of electrons. His idea of particle wave/duality also supported Einstein.
  • James Chadwick

    James Chadwick
    Chadwick discovered the existance of the neutron, a third subatomic particle. He used alpha particles to discover this neutral particle with a mass close to a proton.