Atomic Timeline

Timeline created by Samuel Won
  • -450 BCE

    Empedocles

    Empedocles
    Figured out air is a substance
  • -430 BCE

    Democritus

    Democritus
    Atoms have their own size and shape. Atoms are "uncuttable", they are the smallest particles of matter.
  • -350 BCE

    Aristotle

    Aristotle
    Did not agree with Democritus (shadowed over him). Believed everything was a combination of the 4 elements (Earth, Wind, Fire, Water). Greatly slowed the theory.
  • John Dalton

    John Dalton
    Each element has its own unique property. All matter are made up of tiny particles called atoms. All atoms of a given element are alike, but are different from the atoms of any other elements. Compounds are formed when atoms of different element combine in fixed proportions. A chemical reaction involves the rearrangement of atoms, not a change in atoms themselves. Atoms can't be created, destroyed, or divided, only changed.
  • J.J. Thomson

    J.J. Thomson
    Discovered that atoms are made up of smaller negatively charged particles called electrons and positively charged matter. He discovered this by doing experiments with "cathode ray tubes" Created a model to describe the atom as a sphere filled with positive matter with negative particles mixed in. He referred to it as the plum pudding model.
  • Albert Einstein

    Albert Einstein
    Proved that Brownian Motion of Particles (1827 theory of Robert Brown, Botanist) do exist with his mathematical calculations of watching pollen jitter in water.
    Through statistics, he helped others advance and explain their models with real data.
  • Ernest Rutherford

    Ernest Rutherford
    He decided to shoot a beam of tiny, positively charged particles at a thin sheet of gold foil. He thought that most of the particles would pass right through the gold atoms, which they did. They deflected sideways as well. What surprised him was that some particles bounced right back. Based on the results of his experiment, he proposed a new model of the atom, called the nuclear model. In it, the center of the atom is a tiny, dense positively charged area called the nucleus.
  • Niels Bohr

    Niels Bohr
    Electrons move with a constant speed in fixed, planet like orbits around the nucleus. Electrons move in paths at certain distances around the nucleus. Electrons can move from a path on one level to a path on another level.
  • G.N. Lewis

    G.N. Lewis
    Figured out valence electrons. Covalent bonding of elements. Placed dots (no more that 8) around the symbol of each element to represent the outermost electrons, the Lewis-Dot Diagram.
  • Werner Heisenberg (with help from Niels Bohr)

    Werner Heisenberg (with help from Niels Bohr)
    Uncertainty principle: electrons don’t travel in orbits, just certain regions.
  • Erwin Schrodinger

    Erwin Schrodinger
    Began explaining the wave theory. Electrons move in a wave. Electrons are found in electron clouds, not paths.
  • James Chadwick

    James Chadwick
    Discovered Neutrons in the nucleus of the Atom (neutral particles). Neutrons have a mass nearly equal to the mass of a proton. Unit of measurement for subatomic particles is the atomic mass unit (amu). Assistant to Rutherford. Nobel Prize in 1935. Advanced the work of nuclear fission and the model of the atom.
  • Period:
    -450 BCE
    to

    Atomic Timeline