Historical Perspective of Atomic Discovery

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Historical Perspective of Atomic Discovery
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Democritus

• Circa 400 BC
• A-tom from the Greek for not-cut
• Atomic theory had no scientific proof

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John Dalton

• Early 1800s
• Quantitative analysis of chemical reactions
• Law of conservation of mass
• Billiard ball model

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Proust/Avogadro/Lavoisier/Gay-Lussac

• Mid to late 1800s
• Used quantitative analysis to support
• Law of definite proportions
• Law of multiple proportions

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J.J. Thomson

• 1897 discovered electron
• Cathode ray tube
• Calculated charge to mass ratio of electron
• Hypotheses made by Thomson
• Cathode rays are charged particles
• Cathode rays are composed of parts of atoms

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Robert Millikan

• 1909
• Oil drop experiment
• Calculated charge on the electron
• Allowed for calculation of mass of an electron

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Ernest Rutheford

• 1903
• Gold foil experiment
• Atoms are mostly empty space with a very dense,
  positively charged nucleus

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Scientist Year Experiment Findings/beliefs
Democritus 400 BC Philosophy Matter is Discrete
John Dalton Early 1800s Quantitative Analysis Law of Conservation of Mass Billiard Ball atomic Model
Proust/Avogadro/ Lavoisier/Gay-Lussac Mid to Late 1800s Quantitative Analysis Law of definite proportions Law of multiple proportions
JJ Thomson 1897 Cathode Ray Tube Atoms have Charged areas quantified electrons
Robert Millikan 1909 Oil drop experiment Measured the charge of an electron and calculated the mass of an electron
Ernest Rutherford 1903 Gold Foil Experiment Atoms are mostly empty space Nucleus is very small, very dense, and positively charged
Niels Bohr 1913 Spectroscopy Planetary model
Max Planck 1923 Mathematics Quantum theory
Modern Current Wave mechanical model