The Atomic Theory- a timeline

  • Jan 25, 630


    Democritus was an ancient Greek philosopher who claimed everything is made of atoms, and that the atom was the smallest unit of matter. He is sometimes known as that father of modern science.
  • Dalton Atomic Theory

    Dalton Atomic Theory
    This theory states that all matter is made of tiny particles that are unchanging. It also states that elements are characterized by the mass of the atom.
  • John Dalton

    John Dalton
    John Dalton was an important chemist that came up with the law of conservation of mass, the law of define proportions, and the law of multiple proportions. He postulated that chemical reactions occur when atoms are rearranged.
  • Law of Conservation of Mass

    Law of Conservation of Mass
    States that the mass of an isolated system will remain constant over time. This law was discovered by John Dalton.
  • Law of multiple proportions

    Law of multiple proportions
    The law of multiple proportions says when two element combine to form more than one compound the mass of one element that combines with a given mass of the others is in the ratio of small whole numbers.
  • Law of definite proportions

    Law of definite proportions
    The law of multiple proportions says when two element combine to form more than one compound the mass of one element that combines with a given mass of the others is in the ratio of small whole numbers.
  • Henri Becquerel

    Henri Becquerel
    In 1908 Becquerel was elected Permanent Secretary of the Academie des Sciences. He died at the age of
    55. The SI unit for radioactivity , the Becquerel (Bq), is named after him.
  • J.J. Thomson

    J.J. Thomson
    A British physicist and Nobel Laureate. Credited with discovering electrons and isotopes, inventing the mass spectrometer.
  • Marie Curie

    Marie Curie
    Marie Sklodowska-Curie was a polish physicist and chemist who is famous for her pioneering research
    on radioactivity. She was also the first woman to win a nobel prize, and the only person to win it
    in multiple sciences. Her achievements included a theory of radioactivity, techniques for isolating
    radioactive isotope and the discovery of two elements, polonium and radium.
  • Robert Millikan

    Robert Millikan
    Robert Millikan was an American experimental physicist and Nobel laureate in physics. This was for the
    measurement of the charge on an electron and for work on the photoelectric effect. He is also known
    for his works on the Oil Drop Experiment.
  • Dmitri Mendeleev

    Dmitri Mendeleev
    Dmitri Mendeleev was a Russian chemist and inventor who created the first periodic table of elements. He also predicted some elements that were not yet discovered.
  • Ernest Rutherford

    Ernest Rutherford
    New Zealand-born British chemist and physicist who became known as the father of nuclear physics.
  • Erwin Schrodinger

    Erwin Schrodinger
    In first years of his career he became acquainted with the ideas of Quantum Theory. This knowledge
    helped him work on some problems in the statistical physics. The old quantum theory is a collection of
    results from the years 1900-1925 which predate quantum mechanics.
  • Cathode Ray Tube Experiment

    Cathode Ray Tube Experiment
    In this experiment Thompson observed the deflection of cathode rays by an electric field. This experiment lead to the discovery of the electron.
  • Plum Pudding Model

    Plum Pudding Model
    Thompson discovered that atoms were made of negative and positive charges and believed that the atoms structure was similar to plum pudding, in which the negative electrons floated in a positively charged “pudding.” This was proved incorrect by Rutherford’s model.
  • Oil Drop Experiment

    Oil Drop Experiment
    In 1908 Robert Millikan was a professor at the University of Chicago, and worked on the oil drop
    experiment. This experiment measured the charge on a single electron. It also measured the force on
    tiny charged droplets of oil suspended against gravity between two metal electrodes. Millikan showed
    the results could be explained as integer multiples of a common value (1.592 x 10^-19) charge of a single
  • Rutherford Gold Foil Experiment

    Rutherford Gold Foil Experiment
    Also called Geiger-Madsen experiment. An experiment to probe the structure of the atom, performed by
    Hans Geiger, Ernest Madsen in 1909 under direction of Ernest Rutherford. This experiment showed that atoms hasd nuclei
  • Gold Foil Experiment

    Gold Foil Experiment
    Diffraction of alpha particles (helium nuclei containing two positive charges) by a thin foil made of gold
    metal. Opposite side is zinc sulfide screen that emits a flash of light when struck by an alpha particle.
  • Rutherford Model

    Rutherford Model
    A very small charged nucleus containing much of the atoms mass was orbited by low mass electrons.
    Contained new features of a relatively high central charge concentrated into a very small volume in
    comparison to the rest of the atom.
  • The Bohr Model

    The Bohr Model
    The Bohr Model is a model of an atom containing a small positively charged nucleus orbited by negatively charged electrons.
  • Neils Bohr

    Neils Bohr
    Theorized that any atom could only exist in a discrete set of stable states. He also described the atomic structure in the Bohrs Atomic Model. He believed the energy of the orbit is related to its size.
  • Quantum Mechanical Model

    Quantum Mechanical Model
    Also known as quantum physics or quantum theory. A branch of physics dealing with physical
    phenomena at microscopic scales. Quantum mechanics departs from classical
    mechanics. It also provides a mathematical description of much dual particle-like and wave-like behavior.
    The quantum mechanical model is one of the two models of the atomic structure we use today. This model is based off the quantum theory, and its says matter also has properties associated wit
    and interactions of energy and matter.
  • James Chatwich

    James Chatwich
    James Chatwich discovered the neutron. Neutrons help stabilize the atom.
  • Murray Gell-Mann

    Murray Gell-Mann
    Murray Gell-Mann was an American Physicist that came up with a new classification system for baryons called the eightfold way. He also discovered the quark, which is the building block for neutrons protons and matter.