1. Historical Perspective of Atomic Discovery

2. Democritus Circa 400 BC A-tomfrom the Greek for “not-cut” Atomic theory had no scientific proof

3. John Dalton Early 1800’s Quantitative analysis of chemical reactions Law of conservation of mass Billiard ball model

5. Proust/Avogadro/Lavoisier/Gay-Lussac Mid to late 1800’s Used quantitative analysis to support  Law of definite proportions  Law of multiple proportions

6. 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

8. Robert Millikan 1909 Oil drop experiment Calculated charge on the electron Allowed for calculation of mass of an electron

10. Ernest Rutheford 1903 Gold foil experiment Atoms are mostly empty space with a very dense, positively charged nucleus

12. ScientistYearExperimentFindings/beliefs Democritus400 BCPhilosophyMatter is Discrete John DaltonEarly 1800’s Quantitative AnalysisLaw of Conservation of Mass “Billiard Ball” atomic Model Proust/Avogadro/ Lavoisier/Gay- Lussac Mid to Late 1800’s Quantitative AnalysisLaw of definite proportions Law of multiple proportions JJ Thomson1897Cathode Ray TubeAtoms have Charged areas; quantified electrons Robert Millikan1909Oil drop experimentMeasured the charge of an electron and calculated the mass of an electron Ernest Rutherford1903Gold Foil ExperimentAtoms are mostly empty space Nucleus is very small, very dense, and positively charged Niels Bohr1913SpectroscopyPlanetary model Max Planck1923MathematicsQuantum theory ModernCurrentWave mechanical model