Recitation-03

Recitation-03 - Chemistry 111 Fall, 2005 Prof. Simpson...

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Chemistry 111 Fall, 2005 Prof. Simpson Chemistry 111 Recitation #3 September 21, 2005 A brief recap of the last two lectures … • Correspondence principle • Wave-particle duality Æ waves are characterized by: amplitude, wavelength ( λ ), frequency ( ν ), and speed (v) Æ v = λ ν • Electromagnetic radiation Æ EM spectrum Æ speed of light in a vacuum = constant = 2.998 x 10 8 m s -1 Breakdown of Classical Mechanics Æ Paradox 1 : Blackbody radiation -- UV Catastrophe -- led to Planck's quantization of energy in molecules Æ Paradox 2 : Photoelectric effect -- electrons ejected when light impinges on a metal surface -- Einstein (1905) figured this out, and postulated photons -- E = h ν (h = Planck's constant = 6.6261 x 10 -34 J s -- kinetic energy of the ejected electrons is related to the frequency of the light Æ Paradox 3 : Atomic spectrum -- discrete emission lines for atomic spectra -- an empirical mathematical relationship among them -- Rydberg (1888) Æ Paradox 4 : Rutherford atom -- the nuclear atom -- why doesn’t the electron spiral into the nucleus? • The BohrAtom Æ 4 postulates – including quantized angular momentum Æ allowed radii Æ allowed energy levels Æ how does the Bohr atom solve the challenges to classical mechanics? • Wave mechanics Æ de Broglie and matter-waves Æ the wave-particle duality is complete! Æ λ = h / p = h / mv (for particles )
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Chemistry 111 Fall, 2005 Prof. Simpson Photoelectric effect Example : shine light of λ = 51.0nm onto Cs metal ( Φ = 3.43 x 10 -19 J) (a) what is the energy of the e- ejected? T = h ν - Φ = (hc)/ λ - Φ = (6.636 x 10 -34 J s) (3.00 x 10 8 m s -1 ) / (510.0 x 10 -9 m) - 3.43 x 10 -19 J = 4.68 x 10 -20 J (b) What is the longest wavelength of light that can eject an e - from Cs?
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Recitation-03 - Chemistry 111 Fall, 2005 Prof. Simpson...

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