Atom

History of the Atom

By makennan.mcbryde
  • 400 BCE

    Democritus and His Contributions to the Atomic Theory (click above title for picture)

    Democritus and His Contributions to the Atomic Theory (click above title for picture)
    Democritus contributed to the Atomic Theory by proposing the first idea of the atom, and stating that matter can be divided until you get to the smallest particle, an atom, which is indivisible. This picture shows what the first model of an atom was thought to look like by Democritus.

  • John Dalton and His Revisions to the Atomic Theory (click above title for picture)

    John Dalton and His Revisions to the Atomic Theory (click above title for picture)
    Dalton proposed 5 main points to his Atomic Theory:
    1 all matter is composed of atoms
    2 atoms cannot be created nor destroyed
    3 all atoms of the same element are identical
    4 chemical reactions occur when atoms are rearranged
    5 compounds are formed by the combination of 2 or more different kinds of atoms
    The picture shows a model of what Dalton thought atoms looked like, which is identical to Democritus' because these are macroscopic visuals of an atom meaning Dalton never actually saw an atom.

  • J.J. Thompson and His Plum Pudding Model (click above title for picture)

    J.J. Thompson and His Plum Pudding Model (click above title for picture)
    J.J. Thompson discovered the negatively charged particles of the atom now known as electrons. He did this using a cathode ray tube and found the mass of these particles in the tube were smaller than the mass of Hydrogen, which is when he realized they were actually smaller parts of the atom that were negatively charged henceforth proving Dalton and previous philosophers wrong.

  • Earnest Rutherford and His Gold Foil Experiment (click above title for picture)

    Earnest Rutherford and His Gold Foil Experiment (click above title for picture)
    Rutherford found the protons, neutrons, and empty space of the atom in his Gold Foil experiment. He shot positively charged alpha particles at a thin sheet of gold foil and expected the particles to go through the sheet. Some did, but some were deflected at small angles showing the atom contained a small part, or nucleus, in which the positively charged particles, or protons, lived. This also showed that most of the atom was empty space and the nucleus must carry most of the mass of the atom.

  • Neils Bohr and The Bohr Model (click above title for picture)

    Neils Bohr and The Bohr Model (click above title for picture)
    Bohr is responsible for discovering the idea that electrons orbit, or travel, around the center of the atom, or nucleus, at different energy levels. The closer the electron is to the nucleus the less amount of energy it has, the farther, the more energy it has. He also found that when an electron moves to a greater energy level, and then back down to a lower one, it emits energy or a form of the electromagnetic spectrum.

  • The Modern Atomic Theory (click above title for picture)

    The Modern Atomic Theory (click above title for picture)
    Our current model of the atom accepted today is the Electron Cloud Model. The model is based off quantum theory and the Uncertainty Principle that states it is impossible to know the exact position and speed of an electron, therefore we use probability to see where electrons would most likely be found in the atom. This brings up the concept of electron clouds. We have also accepted that the nucleus contains neutrally charged neutrons, that attribute to the atomic mass.