Atomic Theory Timeline

  • 400 BCE

    Democritus's Model

    Democritus's Model
    His first model had discovered that matter does not divide forever. But since it was Ancient Greece, it had no proof, and very less people believed in him.
  • Dalton's model

    Dalton's model
    Dalton's model was more explainable, so people accepted it more than Democritus's model because Dalton had evidence. His evidence reveals that all matter is made of atoms, atoms cannot be divided, atoms of the same element are exactly the same and atoms the different elements are different, and compounds form by combining 2 or more atoms. His theory has supported the Law of Definite Proportions, meaning that the elements combined are ratios when they react.
  • Thomson's model

    Thomson's model
    Thomson's model was called the "plum-pudding" model and discovered negatively charged particles called electrons. He used cathode rays to show that atoms can be divided. He said that the electrons are scattered in the atom.
  • Rutherford's model

    Rutherford's model
    His model has discovered the nucleus by using gold foil experiments. This suggested that the nucleus was the center of the atom. This was more accurate than Thomson's model because Rutherford's model has positive charge (nucleus) at the center of the atom and the electrons surround it.
  • Bohr's model

    Bohr's model
    He claims that electrons are arranged in circular energy levels around the nucleus. When electrons gain energy, they move up one level. When electrons lose energy, they move down one level.
  • Quantum Mechanical model

    Quantum Mechanical model
    Made by Erwin Schrodinger. His model doesn't know the location of an electron, but predicts it. Also says that the electron "cloud" surrounds the nucleus. In 1932, Chadwick has discovered the neutron, same mass as the proton, but no charge. Bohr's model had energy levels where electrons are placed on, and the quantum mechanical model had an electron "cloud" to surround the nucleus.