Chapter Atomic Theory - Chem I

Chapter Atomic Theory - Chem I - Light has a Wave-Particle...

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Light has a Wave-Particle Duality in Behavior What about Matter having the same Wave-Particle Duality in Behavior?
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Refraction: A wave passing from air into water is refracted (bent at an angle) A particle entering a pond moves in a curved path, due to gravity and the increased resistance of the water(slowing it down) Diffraction : A wave is diffracted through a small opening producing circular waves on the other side A particle or group of particles moves through an opening continuing in an independent path
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Different Behaviors of Waves and Particles Fig. 7.4
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The Diffraction Pattern Caused by Light Passing through Two Adjacent Slits Fig. 7.5
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Demonstration of the Photoelectric Effect Fig. 7.7
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The Photoelectric Effect - I Below the threshold energy,  nothing occurs ! Above the threshold, the  kinetic energy of the ejected  electrons is proportional to  the frequency of the light. Also, when above the  threshold, as intensity of the  light increases, so does the  number of ejected electrons. All metals experience this  effect, but each has a unique  threshold frequency.
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The Photoelectric Effect - II Albert Einstein Theorized Photons (quanta-packets of energy) Won Nobel prize - 1921 Photons have an energy equal to: E = h ν h = Plank’s Constant, and is equal to: 6.6260755 x 10 - 3 4 Jsec
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Photons and the Photoelectric Effect Einstein stated that the change in the photon’s energy was equal to the ejected electron’s energy. Therefore, the photon’s energy equaled the electron’s kinetic energy added to the electron’s binding energy E Total = Electron binding + Electron Kinetic energy
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Photoelectric Effect -I Mininum energy to remove an electron from  potassium metal is 3.7 x 10  -19 J. Will photons of  frequencies of 4.3 x 10 14 /s (red light) and 7.5 x 10 14  /s  (blue light) trigger the photoelectric effect? E  red  = hv = (6.626 x10  - 34 Js)(4.3 x10 14  /s)                  E  red  = 2.8 x 10  - 19  J E  blue  = hv = (6.626 x10  - 34 Js)(7.5x10 14  /s)                  E   blue  = 5.0 x 10  - 19  J
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Photoelectric Effect - II Since the binding energy of potassium is 3.7 x10  - 19  J         the red light will not have enough energy to knock an  electron out of the potassium, but the blue light will eject  an electron ! E  Total  = E  Binding Energy  + E Kinetic Energy of Electron Electron  = E Total  - E  Binding Energy Electron  = 5.0 x 10  - 19 J   -   3.7 x 10  - 19  J               = 1.3 x 10  - 19 Joules
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Fig. 7.14
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Heisenberg Uncertainty Principle It is impossible to know simultaneously both the position and momentum (mass X velocity) with certainty !
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ATOMIC THEORY THE BOHR ATOM : POSTULATES: 1. The elect r on t r aveled in a cir cular pat h
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Chapter Atomic Theory - Chem I - Light has a Wave-Particle...

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