Atomic Structure Timeline

  • May 6, 1000


    NB: Date couldn't be insterted, and therefore the date is incorrect
    Democritus discovered that everything is made of atoms, atoms are indivisible, between atoms lies empty space, atoms are indestructible, they are always moving, there are an infinite number of atoms, and atoms come in different shapes and sizes
  • Isaac Newton proposed the mechanical universe

    Newton suggested that atoms were held together by attractions (forces), and as a result we live in a mechanical universe with small solid masses in motion constantly.
  • John Dalton gave us Valencies!

    Dalton's ideas were that the atoms of an element were the same as its weight, the atoms of different elements had different weights; and atoms combined only in small whole-number ratios to form compounds.
  • George Johnstone Stoney suggested the electron!

    G. J. Stoney proposed that electricity was made of particles called “electrons”. This wasn’t confirmed as this idea was just an estimate.
  • Joseph John Thomson was able to separate molecules according to their weight!

    Thomson carried out an investigation to find that positive rays/cathode rays were streams of negatively charged particles with a mass about 1,000 times smaller than a hydrogen atom. This resulted to the discovery of the electron and the positively charged ion.
  • Max Planck devised the Quantum Theory

    Planck’s idea was that oscillating atoms absorb and emit energy only in bundles. He, along with other scientists established the Quantum Theory. The theory is that energy can only be absorbed or radiated in discrete values or quanta
  • Hantaro Nagaoka proposed the idea of a "nucleus"!

    Nagaoka proposed that the nucleus of an atom was very large and positively charged. He said that electrons that orbited the nucleus were bound by electrostatic forced. His incorrect planetary model was based on his fascination on the planet, Saturn.
  • Robert A. Milikan found that the electron IS negatively charged

    Milikan confirmed that electrons were a negative charge by suspending tiny oil droplets into an electric field.
  • Ernest Rutherford discovered the nucleus!

    He experimented with alpha rays leading him to confirmation of the nucleus. The nucleus is the small, positive charged centre of the atom, which has electrons orbiting around it in shells. He also found that the atom is largely empty.
  • Henry Gwyn-Jeffreys Moseley

    Moseley founded Moseley’s law which associated wavelength and atomic number, thus demonstrating the importance of atomic number over atomic weigh. He also noticed gaps in the periodic table, and predicted elements.
  • Niels Bohr gave us the modern atomic model!

    His idea was that the nucleus is made up of neutrons and protons, with the electrons revolving around the nucleus. He found that each electron shell could only hold a certain number of electrons and after that orbit is full, the next level would have to be used.
  • James Chadwick discovered neutrons!

    Chadwick discovered that atoms also contain neutral particles (no charge) in the nucleus.