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Atomic Theory – People & Contributions

Democritus (400 BC)
Greek philosopher – first description of an “atom”

John Dalton (1803)
English chemist/physicist – Dalton’s Atomic Theory

Johannes Rydberg (1888)
Swedish physicist – Rydberg formula which predicts wavelengths of light emitted from e- changing energy levels in an H atom

J.J Thomson (1897)
English physicist- discovered the electron and the charge/mass ratio of the electron – plum pudding model of the atom

Max Planck (1900)
German physicist – originator of Quantum Theory, Planck’s constant – all energy is emitted/absorbed in discrete packets called quanta

Albert Einstein (1909)
German physicist – wave-particle duality of light – photons, explanation of photoelectric effect

Robert Millikan (1910)
American physicist – Oil-Drop experiment determined the charge on an electron

Ernest Rutherford (1911)
New Zealand/English physicist – gold foil experiment – discovered that the mass and positive charge of an atom is in the nucleus

Niels Bohr (1913)
Danish physicist – Bohr model of the atom – e- in orbits at certain energy levels

Henry Mosley (1913)
English physicist – linked atomic number to a real physical quantity

Louis De Broglie (1924)
French physicist – wave-particle duality for all matter

Wolfgang Pauli (1925)
Austrian physicist – Pauli Exclusion Principle – electrons occupying the same orbital must have opposite spins

Friedrich Hund (1925)
German Physicist – Hund’s Rule – electrons are placed in separate orbitals of the same energy before a second is placed in any

Erwin Schroedinger (1926)
Austrian physicist – wave equation which describes changes in the quantum state of a physical system over time

Werner Heisenberg (1927)
German physicist – Heisenberg Uncertainty Principle – key development of quantum theory, you cannot know precisely where a particle is and where it is going

James Chadwick (1932)
English physicist – discovered the neutron

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