Origins of the atomic theory


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Origins of the atomic theory

  1. 1. Origins of the Atomic TheoryPhysical Science2009-2010psquires
  2. 2. The Development of the Atomic Theory♦Democritus and Dalton:♦atomic theory
  3. 3. Democritus♦Greek philosopher ~ 300 BC♦Limit to “smallness”♦All matter consists of tiny, indestructible particles called atoms♦Atomos – indestructible
  4. 4. John Dalton First serious atomic theory♦English scientist♦Studied the properties of gases♦“Reinvented” the idea of atoms♦Published in 1803
  5. 5. Dalton’s atomic theory - 1803 1. Elements are composed of tiny, discrete, particles called atoms.
  6. 6. Dalton’s atomic theory - 18032. Atoms are indivisibleand indestructible and donot change their identityduring reactions.
  7. 7. Dalton’s atomic theory - 18033. Atoms of the sameelement are identical inmass and chemical andphysical properties. Atomsof different elements aredifferent.
  8. 8. Dalton’s atomic theory - 18034. Atoms combine to formcompounds in simple,whole-number ratios.Law of Definite Proportions
  9. 9. Dalton’s atomic theory - 18035. Atoms combine indifferent ratios to maketwo or more compounds.Law of Multiple Proportions
  10. 10. The Development of theAtomic Theory♦Thomson: CRT’s and the electron
  11. 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. 12. Cathode Ray TubeIt was also used by J. J. Thomson Cathode Anode High voltage +
  13. 13. That particle was called the … TheThe electron electron The Electron The electronThe electron Discovered in 1897 The electron By J. J. Thompson
  14. 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. 15. The Development of theAtomic Theory♦Rutherford: “Gold Foil Experiment”
  16. 16. The Gold Foil Experiment Top ViewSide View
  17. 17. The Gold Foil Experiment Gold foil Fluorescent detector ZnS Alpha particle sourceAll of this was in avacuum chamber.
  18. 18. The Gold Foil Experiment Most of the α particles went… …straight through the gold foil, undeflected.The gold is mostly “empty space.”
  19. 19. Alpha Particles Alpha particles are helium nuclei. Two protons + and + two neutrons.The alpha particle is positively charged.
  20. 20. Gold Foil Experiment: Resultsα source + Small, dense, positively charged nucleus of gold
  21. 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. 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. 23. Bohrdiagram