The History of Atomic Theory

  • 300


    Aristotle is credited for discovering the four "elements", which he named air, fire, water, and earth. He believed in reasoning in substitution of scientific experiments and dismissed Democritus' album as "worthless". -DL (since timetoast doesn't allow for BC dates, it looks out of order, when it is not. the correct date is mid300BC -MW)
  • 400

    Democritus of Adbera

    Democritus of Adbera is credited for the term atomos, meaning indivisible. He was the first to identify the possibility of an atom and deem it as the smallest piece of matter. (the date can't be set in BC on timetoast, so it looks out of order, when it should be ~400BC) -MW
  • John Dalton

    John Dalton is credited as the father of the modern atomic theory. The theory is composed of five parts, which includes elements being composed of atoms and that element's atoms are identical in mass. -DL (Because timetoast doesn't allow timespans in a good way, the correct span for this information is 1803-1808) -MW
  • John Dalton's Atomic Theory

    The atomic theory, as proposed by John Dalton, is composed of five parts.
    1) Elements are composed of extremely small particles known as atoms.
    2) Atoms of a given element are identical in size, mass, and other properties; atoms of different elements are different
    3) Atoms cannot be subdivided, created, or destroyed.
    4) Atoms of different compounds combine in simple, whole-number ratios to form chemical compounds.
    5) In chemical reactions, atoms are combined, separated, or rearranged.
  • John Dalton's Solid Sphere Model

    The solid sphere model was John's Dalton's explanation of the atom. It was a solid, indestructible sphere. It didn't include a nucleus or subatomic particles. However, it didn't explain a lot, and was quickly replaced by other things.
  • Robert Millikan

    Robert Millikan is credited for measuring the charge of an electron. He also performed the oil drop experiment, which he completed with JJ Thomson.
  • Joseph John Thomson

    Joseph John Thomson is credited with describing the nature of cathode rays. He also created the plum pudding model of the atom and discovered the electron.-DL
  • Max Planck

    Max Planck is credited with stating that atoms can emit "quanta". Einstein used this scientist's work to study photons. -MW
  • JJ Thomson's plum pudding model.

    The plum pudding model, proposed by JJ Thomson, was seen as the atom before the discovery of the atomic nucleus. The model is composed of electrons surrounded by positive charge to balance the negative charges. The "plums" were neutralized by the "pudding". This model of the atom was disproved in 1909, by Ernest Rutherford.
  • Robert Millikan's Oil Drop Experiment

    The oil drop experiment was meant to measure the charge of electrons. It involved balancing gravitational force with the upward buoyant forces on oil suspended between two metal electrodes. Through this experiment, Millkian and his partner deemed the approximate value of the electron as 1.5924(17)x10^-19C, which is within 1% of the present-day accepted value.
  • Ernest Rutherford's Gold foil Experiment

    The Gold foil experiment consisted of a series of tests in which positive charges were sent through a layer of gold foil. The expected result was the the charges would just pass through because of the theory of the plum pudding model. However, the results were unexpected, as various charges were aimed all directions, bouncing off of something in teh atom. This led to the discovery of the atomic nucleus, the planetary model of the atom, and the downfall of the plum pudding model.
  • Ernest Rutherford

    Ernest Rutherford is credited with the gold foil experiment. He stated that atoms have a small positively charged nucleus, and the remainder is empty space. He also predicted the existence of neutrons. (because timetoast doesn't allow for timespans, the correct labeling for this is 1911-1918) -MW
  • Rutherford's planetary model of the atom

    Rutherford's model was based off of conclusions and results of is gold foil experiment two years ealier. In this model, the center of the atom is the positively charged atomic nucleus, surrounded by electrons in direct planetary paths around the nucleus, like planets around the Sun. This model, however inaccurate, is what the public still recognizes as the symbol of the atom.
  • Niels Bohr

    Niels Bohr is credited with the planetary model of the atom. He also stated that electrons traveled in specified energy levels and that spectrum lines are produced when electrons move. -MW
  • The Bohr model of the atom

    The Bohr model of the atom depicts an atom with a small, positively charged nucleus surround by electrons that travel in circular orbits around this nucleus. It was an improvement fo the plum pudding model and extremely similar to the Rutherford planetary model.
  • Louis deBrogile

    Louis deBrogile is credited with stating that electrons have properties of both waves and particles. There are also groups of waves named after this scientist. -DL
  • Quantum Mechanical Model

    This model was devised by Werner Heisenburg. It is the present-day accepted model of the atom. Because of the many different theories, such as Heisenburg's uncertainty principle and Bohr's and Rutherford's models of the atom, Heisenburg devised this model. This means that the atom is devised of a small nucleus which has protons and neutrons but the electron "cloud" that surrounds the nucleus is full of electrons traveling in different directions at different momentums.
  • Werner Heisenburg

    Werner Heisenburg is credited with the "uncertainty principle", which states it is impossible to determine the position and momentum of a particle at the same time. He is also credited with the "cloud" model, also known as the quantum mechanical model.-MW
  • Uncertainty Principle

    The uncertainty principle states that there is a fundamental limit on the accuracy with which certain properties of a particle, like how fast it's going or where it is, can't be exactly determined or known. It was a key discovery in early quantum theory.
  • Erwin Schrodinger

    Erwin Schrodinger is credited with showing mathematically that waves can be used to describe electrons in atoms. He also determined the probability location of electrons in atoms. -DL
  • James Chadwick

    James Chadwick was credited with the discovery of the neutron and that he helped with the development of the nuclear model.