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Period: 431 BCE to 404 BCE
The Peloponnesian War
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400 BCE
Democritus (460 BCE – 370 BCE)
Proposed the idea of the atom as an indivisible particle -
John Dalton(1766–1844)
Introduced the "marble" model, suggesting atoms are indivisible, solid spheres -
The Louisiana Purchase
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Period: to
Napoleonic War
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Michael Faraday (1791–1867)
Demonstrated that atoms could be influenced by electric and magnetic fields -
Eugen Goldstein (1850–1930)
Discovered canal rays (protons), showing atoms had positive charges -
JJ Thomson (1856–1940)
Discovered the electron and proposed the "plum pudding" model -
The Spanish–American War
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Robert Millikan (1868–1953)
Measured the charge of the electron via the oil drop experiment, confirming the quantization of charge -
Ernest Rutherford (1871–1937)
Proposed the "nuclear" model with a dense central nucleus surrounded by electrons -
Neils Bohr (1885–1962)
Introduced the "solar system" model where electrons orbit the nucleus in defined energy levels -
Period: to
World War I
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The Russian Revolution
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Edwin Schroedinger (1887–1961)
Developed the "electron cloud" model using wave mechanics, depicting probabilistic electron locations -
Werner Heisenberg (1901–1976)
Formulated the Uncertainty Principle, showing limits in measuring atomic properties precisely -
Period: to
Great Depression
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James Chadwick (1891–1974)
Discovered the neutron, refining the "electron cloud" model to include neutrons in the nucleus -
Adolf Hitler raise to power