History of the Atom

  • Conservation of Mass

    Conservation of Mass
    Antoine Lavoisier discovers that during a chemical reaction, matter can not be created or destroyed becoming the law of the conservation of mass.
  • Dalton's Theory

    Dalton's Theory
    In 1803 John Dalton Developed his theory of the atom stating,
    a) All matter is made of atoms. Atoms are indivisible and indestructible.
    b) All atoms of a given element are identical in mass and properties
    c) Compounds are formed by a combination of two or more different kinds of atoms.
    d) A chemical reaction is a rearrangement of atoms.
  • Gay-Lussac's Theory

    Gay-Lussac's Theory
    J.L. Gay-Lussac formed a theory that stated the volumes of gases are in the ratio of small whole numbers.
  • Definite Proportions

    Definite Proportions
    Joseph Proust found that the elements in a substance were always found in the same proportion as long as the substance remained constant.
  • Uranium's Film

    Uranium's Film
    French Scientist Henry Becquerel discovers a photographic fil around the element Uranium.
  • Radiation from Elements

    Radiation from Elements
    Marie and Pierre Curie discovered that the elements Radium and Uranium give off radiation.
  • Cathode Rays

    Cathode Rays
    Scientist J.J. Thomson discovered that cathode rays were made up of electrons.
  • Quantum Theory

    Quantum Theory
    Planck believed that energy was given off in little packets called quanta. He also discovered that the frequency was related to the energy of the light emitted.
  • Einstein's Hypothesis

    Einstein's Hypothesis
    Einstein theorized that energy and mass were equivalent through the formula E=MC2 or mass times the speed of light squared equals energy.
  • Milikan's Measurement

    Milikan's Measurement
    American Scientist Robert Andrews Millikan correctly measured the charge of an electron.
  • The Nucleus

    The Nucleus
    Physicists Rutherford, Bohr, Geiger, and Marsden found that the atom was composed mostly of free space and that some type of core at the center of the atom held the protons and neutrons which would later be known as the nucleus.
  • Wavelength of X-Rays

    Wavelength of X-Rays
    English Scientist Henry Moseley found that the wavelength of the X rays was dependent on the metal used as an anode.
  • Electron Orbits

    Electron Orbits
    Bohr discovered that electrons occupied certain orbital paths and that they could absorb or emit energy only in integers.
  • The Third Particle

    The Third Particle
    English Physicist Lord Rutherford predicts that there is a third atomic particle.
  • Neutron Discovery

    Neutron Discovery
    English Scientist James Chadwick finds that there are other high energy particles called neutrons with no atomic mass that also had around the same mass as the proton.