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442BC- Democritus came up with the thought that all matter is made up of individual elements.
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1803- John Dalton decided on a theory that everything is made of atoms of different weights, he also questioned whether atoms where sphere in shape.
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1870- Sir William Crookes created an early model for the Cathode Ray tube, which is high-vacuum tube where cathode rays make a luminous image on a fluorescent screen, nowadays used for TVs.
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1898 - Pierre and Marie Curie speculated that radioactive particles cause atoms to break down.
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Joseph John Thomson used his knowledge of cathode rays and their properties to discover the electron.
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1900- Max Planck proposed the quantum theory, which says that electromagnetic energy could only be emitted in quantized form.
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1905- Albert Einstein formed generic theories of relativity and saw light as wave and particle. This was the basis of nuclear energy.
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Known as the elementary charge, Robert Millikan measured the charge of a single electron.
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Using the gold foil experiment, Rutherford proposed the theory for the structure of an atom and showed the existence of atomic nucleus. (A atomic nucleus is the small, part made up of of protons and neutrons at the center of an atom.
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1913- Neil Bohr created the Bohr Atomic model. While doing so, he incorporated the Planck quantum theory, finding that when electrons change orbits they emit a quantum of various energy.
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1926- Erwin Shrödinger developed the Schrodinger equation which illustrates how the quantum state of a system changes with time.
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1931- James Chadwick discovered the neutron component of the atomic nucleus, which shows the nuclear division of uranium. Because of his findings, it is now possible to establish heavier elements than uranium in a lab.
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1938- Otto Hahn and Lise Meitner discover nuclear fission.
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1944-1958 - Seaborg identified nine elements – americium (95), curium (96), berkelium (97), californium (98), einsteinium (99), fermium (100), mendelevium (101), and nobelium (102) and Seaborgium. (Alongside his colleagues he found 11 elements, during his career.)
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1951- Glenn Seaborg developed Iodine 131 for Thyroid disease which is a type of radioactive iodine, as well as many discoveries in Nuclear medicine.
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1964- Murray Gell and George Zweig show that elementary particles that have no substructure and therefore can't be split, using the Quark model.
