Stylised atom with three bohr model orbits and stylised nucleus (white background)

Nolan's Atomic Theory Timeline

  • 700 BCE

    Asharya Kanada

    Asharya Kanada
    Asharya Kanada, in theory, came up with the theory of the atom well before Dalton's time which is a surprise to most people. He was believed by many that he was the first person to realize the idea and theory of a particle of matter being indestructible. His theory came to him while he was eating, he could no longer divide his food into any smaller pieces, meaning that atoms could not be divided at a certain point. he called this the "Anu" which means atom.
  • 480 BCE


    Empedocles theorized that all matter is made up of four composed elements. Those four elements are earth, fire, water, and air. Instead, he named earth, fire, water and air "roots" instead of elements that we call them now. He believed everything was composed of these four roots and nothing more and nothing less. This lead to other scientists and philosophers expanding on his initial thinking and eventually lead to more complex theories of matter and the atomic theory.
  • 400 BCE


    He theorized and came up with the atomos, which he reasoned as having a compound or an atom, it can be divided into smaller and smaller pieces to the point where it is indivisible. He also theorized that atomos was specific to the material that the compound is made up.
  • 1490


    Alchemy is an old form of chemistry that set the foundation for the development and the creation of the atomic theory. The main foal of alchemy was to figure out a way to transform ordinary metals into precious gold. This was there quest to and for purity. They wanted to find and or make a substance called the "philosopher's stone" which was when heat was added to non-precious metals, would then transform to gold. Not only was alchemy scientific, but it was also a spiritual tradition.
  • Dalton

    His contribution to the atomic theory was the creation of properties associated with atoms which he called Dalton's Atomic Theory. He proposed that everything is made of atoms that cannot be created nor destroyed, all atoms of an element are identical, different elements differ in atom size and mass, compounds are created from different whole-number combinations of atoms, and chemical reactions cause rearrangement of atoms.
  • Marie Sklodowska Curie

    Marie Sklodowska Curie
    She was the first woman to win two Nobel Prizes, one in physics and one in chemistry. Her contributions to the atomic theory were her discovery of radioactivity, polonium, and radium. She discovered that uranium cast-off rays that were than X-rays found by another physicist. She took his theory one step further. She was able to determine that the atomic structure of uranium was the reason for the rays being emitted. She then named the phenomenon "radioactivity".
  • Planck

    Max Planck was the originator of the quantum theory of energy. He was awarded a Nobel Prize in 1918 for the work he had done. His contribution was determining the amount of energy was at each quantum level. His studies in thermodynamics helped him in the development of the quantum theory as his knowledge from thermodynamics helped him created experiments to test the amount of energy at each level. His quantum level helped Einstein with the properties of light.
  • J.J. Thomson

    J.J. Thomson
    His contribution to the atomic theory was the discovery of the electron. He believed the atom consisted of positive and negative charges which most scientists did not believe in. With the atom being both positive and negative, it would balance out the charge of the atom. He came up with the Plum Pudding model to demonstrate the shape of the atom.
  • Hantaro Nagaoka

    Hantaro Nagaoka
    His contribution to the atomic theory was his development of the Saturnian system. This system showed that postulated atoms in his model were inherently unstable because the atom would continuously under the radiation process, the electrons would gradually lose energy and would eventually be so weak that they would leave their orbitals and enter into the nucleus. And because of this, the electron could not remain in any orbital indefinitely, it would eventually end up in the nucleus.
  • Einstein

    Einstein's contribution to the atomic theory was that light moved in waves. This allowed other physicists to develop the quantum theory because of Einstein's contributions. He also determined that atoms can emit and absorb photons. In a paper he wrote, he explained that light absorption has the ability to release electrons from atoms. Einstein was also able to determine the size of atoms as well as the size of molecules
  • Rutherford

    Rutherford brought a new perspective as to how the atom should be represented. He overturned Thomson's model with the famous gold-foil experiment. This experiment showed that the electrons orbited around the nucleus of the atom and that there was a nucleus. His model had protons and neutrons located in the nucleus and the electrons were not as they orbit around the nucleus.
  • Niels Bohr

     Niels Bohr
    Niels Bohr worked with Rutherford to create the theory of the nucleus and electrons being present in an atom. His contributions consisted of placing electrons in distinct energy "shells". Those electrons would then determine the reactivity of the elements. He put the electrons in distinct shells or levels that would determine how the electrons would move between atoms when reacted together.
  • Heisenberg

    His contribution to the atomic theory was the creation of quantum mechanics. He believed that electrons did exist in different energy shells, however, there was no way to determine where the actual electron position was without moving it. This is now called the Heisenberg uncertainty principle.
  • deBroglie

    deBroglie proposed the idea that electrons moved in waves. This theory was somewhat theorized by Einstein 20 years prior. His proposal answered the questions that had been created by calculations of the motion of electrons within an atom. Through experiments that he conducted, he came to the conclusion that electrons did move in waves was because the wave properties restricted the shape of the atom. This was a building block to the creation of the quantum theory.
  • Pauli

    Pauli theorized that no two electrons in an atom could have identical quantum numbers. This would then become the Pauli principle. The quantum number that could not be identical was the spin number. He then theorized the sping theory and that two electrons would spin in opposite directions, one being "spin up" and the other "spin down". Spin up had a positive value and spin down had a negate value.
  • Satyendra Nath Bose

    Satyendra Nath Bose
    His contribution to the atomic theory was deriving Planck's quantum radiation law without referencing classical physics. He was able to do this by counting states with identical properties. This would later prove seminal in creating the field of quantum statistics. He would then send this Einstein in Germany, where Einstein would adopt his idea and extend it to atoms. This lead to the phenomena that was called the Bose-Einstein Condensate.
  • Schrödinger

    Schrödinger took Bohr's theory and took it one step forward. He used a mathematical equation to determine where the electron would be in each shell. This model is known as the quantum mechanical model. Unlike Bohr, this model does not define the exact path the electron would take, instead, it predicts the odds of the location the electron will be in. This can be seen as dense clouds, the denser the cloud the higher probability the electron will be there.
  • Chadwick

    His contribution to the atomic theory was proving the existence of neutrons in the nucleus of an atom. Using mathematical and experimental proof, he was able to determine that the neutron would serve as a "buffer" for the positively charged protons in the nucleus. This would allow the nucleus to become more stable.
  • Lise Meitner

    Lise Meitner
    She discovered that uranium underwent spontaneous fission whenever it absorbed an extra proton. She studied radioactivity of atoms which lead her to the discovery of spontaneous fission. This discovery leads to the first development of the atomic bomb during the Manhattan Project during WWII. This discovery contributed to the development of nuclear weapons which all stem back to the atomic level of atoms and how they decay and emit radiation through various forms.
  • Ronald J. Gillespie

    Ronald J. Gillespie
    His contribution to the atomic theory was that he looked at expanding on the idea of Valence shell electron pair repulsion of molecular geometry. He also developed the LCP theory which was for some molecules, their geometry could be predicted on a basis of ligand-ligand repulsions. He also did work on calculating the covalent radius for fluorine which was more difficult than other atoms because of the high electronegativity compared to its small atomic radius size.
  • Robert J. LeRoy

    Robert J. LeRoy
    Robert J. LeRoy studied the behaviour of molecules and atoms but more importantly the forces that occur in the atom or molecule. His work was very successful that in Ontario highschool textbooks, there is the Leroy radius, which is a mathematical technique for defining the radius of a small molecule. This technique is important as it is important to the understanding of how the forces in an atom work inside and outside of the radius boundary.
  • Richard F.W. Bader

    Richard F.W. Bader
    His theory was that the density of the electrons was in fact important when trying to explain the behaviour of atoms in molecules. To his theory, there is no such thing as atomic orbitals in the molecule. His theory was to use the physics side of chemistry to try and explain what a bond is and how it actually works. He used a software program called AIMPAC, that is able to predict the property of molecules based on atoms present in the molecule.