type: timeline | subtopic: History of Atomic Theory
| Year | Scientist | Discovery/Model | Key Implication |
|---|---|---|---|
| 1803 | John Dalton | Atomic theory: atoms are indivisible solid spheres | Matter is made of discrete particles |
| 1897 | J.J. Thomson | Discovery of the electron | Atoms have sub-atomic particles (negative charges) |
| 1904 | J.J. Thomson | "Plum pudding" model: electrons embedded in uniform positive sphere | First structural model of the atom |
| 1909–1911 | Geiger, Marsden, Rutherford | Alpha-scattering experiment | Tiny, dense, positive nucleus; mostly empty space |
| 1911 | Ernest Rutherford | Nuclear model of the atom | Planetary model: electrons orbit the nucleus |
| 1913 | Niels Bohr | Quantum model with stationary orbits | Explains hydrogen spectrum; quantized energy levels |
| 1913 | Henry Moseley | X-ray spectroscopy: atomic number Z | Z (not mass number A) determines element identity |
| 1919 | Rutherford | First artificial nuclear reaction (α + ^{14}N → ^{17}O + p) | Nuclear transmutation is possible |
| 1932 | James Chadwick | Discovery of the neutron | Nucleus contains protons AND neutrons |
| 1935 | Hideki Yukawa | Proposed meson as carrier of strong nuclear force | Theoretical basis for nuclear binding |
| 1938 | Hahn, Strassmann, Meitner | Discovery of nuclear fission of U-235 | Enormous energy release possible |
| 1942 | Enrico Fermi | First controlled nuclear chain reaction | Nuclear reactor concept demonstrated |
| 1952 | USA | First hydrogen bomb (fusion) | Thermonuclear energy demonstrated |
| 1964 | CERN | Quark model proposed (Gell-Mann) | Nucleons have internal structure (quarks) |
| 2012 | CERN/LHC | Higgs boson discovered | Mass generation mechanism confirmed |