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400 BCE
Democritus
Theorized the existence of atoms but was rejected by Aristotle and many others -
Antoine Lavoisier
Discovered the Law of Conservation of Mass where matter cannot be created or destroyed -
John Dalton
Discovered all matter was made of atoms which are indestructible and unchangeable, different from Democritus's theory -
J.J. Thomson
Discovered electrons and came up with the "plum pudding" model of the atom where negative particles were located in a positive atom -
Marie Curie
Discovered polonium and radium which were more radioactive than uranium, proving atoms were not as stable and invariable as once thought to be -
Max Planck
The originator of quantum theory which helped further understanding of atomic processes -
Albert Einstein
Explained the photoelectric effect where electrons are ejected when light hit a metal plate a certain way and experimentally proved the existence of atoms and calculated their size by analyzing how tiny particles moved when suspended in water -
Robert Millikan
Determined the specific charge of electrons with his "oil drop" experiment -
Ernest Rutherford
His "gold foil" experiment allowed him to discover the nucleus which was positively charged with electrons floating in the empty space around it, replaced Thomson's "plum pudding" model -
Niels Bohr
Proposed that electrons orbited in set levels away from the nucleus, which led to his "planetary" model, electrons emit energy when it drops to a level closer to the nucleus and absorb energy when it gets further away -
Louis De Broglie
Predicted the wave nature of electrons based on Einstein's theory -
Werner Heisenberg
Introduced quantum mechanics in the atomic theory which led to the discovery of allotropic forms of hydrogen, cannot prove Bohr's planetary orbits of electrons actually exist -
Erwin Schrodinger
Used mathematical equations to predict the location of electrons based on De Broglie's theory and created the quantum mechanical model of the atom -
James Chadwick
Proved the existence of the neutron which had no electrical charge by bombarding beryllium atoms with alpha particles
