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Origins of the atomic theory


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  • 1. Origins of the Atomic TheoryPhysical Science2009-2010psquires
  • 2. The Development of the Atomic Theory♦Democritus and Dalton:♦atomic theory
  • 3. Democritus♦Greek philosopher ~ 300 BC♦Limit to “smallness”♦All matter consists of tiny, indestructible particles called atoms♦Atomos – indestructible
  • 4. John Dalton First serious atomic theory♦English scientist♦Studied the properties of gases♦“Reinvented” the idea of atoms♦Published in 1803
  • 5. Dalton’s atomic theory - 1803 1. Elements are composed of tiny, discrete, particles called atoms.
  • 6. Dalton’s atomic theory - 18032. Atoms are indivisibleand indestructible and donot change their identityduring reactions.
  • 7. Dalton’s atomic theory - 18033. Atoms of the sameelement are identical inmass and chemical andphysical properties. Atomsof different elements aredifferent.
  • 8. Dalton’s atomic theory - 18034. Atoms combine to formcompounds in simple,whole-number ratios.Law of Definite Proportions
  • 9. Dalton’s atomic theory - 18035. Atoms combine indifferent ratios to maketwo or more compounds.Law of Multiple Proportions
  • 10. The Development of theAtomic Theory♦Thomson: CRT’s and the electron
  • 11. J. J. Thomson♦Cathode rays - cathode ray tube♦Attracted to positive electrode♦Thought they might be atoms♦Had same charge to mass ratio regardless of metal in the cathode♦Particle must be common to all matter, a subatomic particle
  • 12. Cathode Ray TubeIt was also used by J. J. Thomson Cathode Anode High voltage +
  • 13. That particle was called the … TheThe electron electron The Electron The electronThe electron Discovered in 1897 The electron By J. J. Thompson
  • 14. J. J. ThomsonIf that were the case, then theelectron would be much smallerthan the smallest atom, … showing for the first time that matter is made up of particles smaller than atoms.Thomson tried to measure thefundamental charge on the electron.
  • 15. The Development of theAtomic Theory♦Rutherford: “Gold Foil Experiment”
  • 16. The Gold Foil Experiment Top ViewSide View
  • 17. The Gold Foil Experiment Gold foil Fluorescent detector ZnS Alpha particle sourceAll of this was in avacuum chamber.
  • 18. The Gold Foil Experiment Most of the α particles went… …straight through the gold foil, undeflected.The gold is mostly “empty space.”
  • 19. Alpha Particles Alpha particles are helium nuclei. Two protons + and + two neutrons.The alpha particle is positively charged.
  • 20. Gold Foil Experiment: Resultsα source + Small, dense, positively charged nucleus of gold
  • 21. Rutherford’s Nuclear AtomAlpha particles were repelled by…… a small, dense, positivelycharged nucleus. Almost all the mass of an atom is in the nucleus.Electrons are located outside thenucleus.
  • 22. Niels Bohr♦ Electrons travel in fixed orbits around the atom’s nucleus.♦ Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light.♦ Later other physicists expanded his theory into quantum mechanics.♦ This theory explains the structure and actions of complex atoms.
  • 23. Bohrdiagram