History of the Atom Timeline

  • Democritus
    400 BCE

    Democritus

    He suggested that all matter was formed of different types of tiny discrete particles and that the properties of these particles also determined the properties of matter.
  • John Dalton

    John Dalton

    He found that all matter was composed of atoms, indivisible and indestructible building blocks.
  • Dmitri Mendelev

    Dmitri Mendelev

    He is known for his work on the Periodic Law and creation of the first Periodic table.
  • Eugen Goldstein

    Eugen Goldstein

    He was one of the first to observe the proton.
  • J.J. Thomson

    J.J. Thomson

    He discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged.
  • Max Planck

    Max Planck

    He is best known as the originator of the quantum theory of energy for which he was awarded the Nobel Prize in 1918.
  • Robert Millikan

    Robert Millikan

    He helped us for allowing us to find the calculation of the mass of the electron and the positively charged atoms.
  • Ernest Rutherford

    Ernest Rutherford

    He was the first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons, which became known as the Rutherford model.
  • Niels Bohr

    Niels Bohr

    He developed a theory for the hydrogen atom. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted.
  • Werner Heisenberg

    Werner Heisenberg

    He discovered a way to formulate quantum mechanics in terms of matrices.
  • Erwin Schrodinger

    Erwin Schrodinger

    He took the Bohr model further. He described the likelihood of finding an electron in a certain position.
  • James Chadwick

    James Chadwick

    He found that neutrons are located in the center of an atom, in the nucleus along with the protons. They have neither a positive nor negative charge, but contribute the the atomic weight with the same effect as a proton.