Democritus model


  • Period: 350 to 450


  • 400

    Aristotle - B.C.

    Aristotle disliked the idea of the atom and believed that every substance was made from proportions of air, earth, fire and water.
  • 476

    Fall of Roman Empire - A.D.

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  • Period: to


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  • Joseph Proust

    He stated his law of definite proportion stating that compounds will have the same proportions of elements in them.
  • John Dalton

    Concluded that atoms of the same element are the same but differ from atoms of different elements based on atomic weight. Also he states that atoms of one element can combine with another element to form a compound. Also states that atoms cant not be created, divided into smaller particles.
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  • Henri Becquerel

    Becquerel showed that the rays emitted by uranium caused gases to ionize and that they differed from x-rays in that they could be deflected by magnetic fields.
  • J.J. Thomson

    J.J. Thomson
    Found that atoms contained particles which were called electrons. Found that the electrons were negatively charged.
  • Max Planck

    Found that the action of an electron, angular momentum, bound into an atom or molecule is limited but, an unbound electron does not show limited energy levels,
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  • Ernest Rutherford

    Ernest Rutherford
    Rutherford suggested that there was a dense positively charged nucleus being orbited by small negatively charged electrons.
  • Robert Millikan

    Millikan discovered the mass of an electron is one thousandth of the mass of even the smallest atom.
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  • Niels Bohr

    Niels Bohr
    Bohr Model;
    States that electrons travel in small orbits around the atom’s nucleus.
  • Louis de Broglie

    He suggested that electrons could move like waves and not only particles, thus answering several holes in the Bohr model.
  • Erwin Schrodinger

    Was accredited of finding an electron around the atom. Does not show exact but a probable location.
  • Werner Heisenberg

    He worked out the uncertainty principle which was an equation for the principle the by hitting an electrom with a gamma ray you could measure its location or momentum, but the more precisely one was measured the less precisely the other is measured.
  • Quantum Mechanical Model

    Quantum Mechanical Model
  • James Chadwick

    The Discovery of the Neutron;
    Proved that the atomic nucleus contained a neutral charged particle called the Neutron.
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  • Democritus - B.C.

    Democritus - B.C.
    States that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size.
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