History of the Atom

Timeline created by nataliewendorf
  • -440 BCE

    Democritus

    Democritus
    He discovered the universe was made of tiny atoms that formed larger units. Atoms make up matter and are separated by empty space for them to move. Atoms are solid and unchangeable. Atoms differ is size and shape.
  • John Dalton

    John Dalton
    He continued Democritus’ ideas by creating his own modern atomic theory. He discovered atoms are indivisible and indestructible with different weights and chemical properties. Atoms can’t be created or destroyed and combine together to form compounds. Elements are made of atoms.
  • Dmitri Mendeleev

    Dmitri Mendeleev
    He discovered the periodic table was configured by the element’s atomic weight.
  • Eugene Goldstein

    Eugene Goldstein
    He discovered that electrons travel from the negative cathode to the positive and an additional ray travels in the opposite direction. So this concluded that they carry the opposite charge. They were known as cathode rays.
  • JJ Thomson

    JJ Thomson
    He discovered the electron in 1897 and proved atoms can be divided. He determined that negatively charged particles exist.
  • Max Planck

    Max Planck
    He used quantization to prove how light is given off. He used radiation coming from an object that glowed to form energy.
  • Robert Millikan

    Robert Millikan
    He proved how to find the charge of an electron in 1909. He conducted experiments to determine the electric charge carried by one electron. His experiment concluded that an electron’s mass is 1000 times smaller than the lightest atom.
  • Ernest Rutherford

    Ernest Rutherford
    He discovered the nucleus and in 1920 he came up with protons to be positively charged particles. He also theorized the neutrons existence in 1920.
  • Niels Bohr

    Niels Bohr
    He used hydrogen atoms to show the quantum theory. It proved energy only transfers in certain quantities. Electrons move around the nucleus.
  • Erwin Schrodinger

    Erwin Schrodinger
    He came up with the quantum model to distribute electrons in an atom using quantum numbers. It requires three quantum numbers to describe orbitals in an electron.
  • Werner Heisenberg

    Werner Heisenberg
    He determined that a person cannot know the position and velocity of an electron at the same time. He discovered how to formulate quantum mechanics into matrices. He also contributed to the hydrodynamics theory and the atom’s nucleus.
  • James Chadwick

    James Chadwick
    He discovered that neutrons are in an atom's nucleus.