reader5 - Electrons in Atoms Rutherford atom Electrons are...

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Electrons in Atoms Rutherford atom Electrons are not drawn into nucleus Petrucci 8.5 Quantum Mechanics Tiny, fast objects (like electrons around the nucleus) behaves differently than macroscopic objects To describe the behavior of such object we need to use quantum mechanics Wave-Particle duality Quantum particles move from one point to another as if they are waves At a detector they always appear as discrete lumps of matter Heisenberg’s Uncertainty principle Wave-Particle duality causes funda- mental limitations on the simulta- neous determination of position and momentum Petrucci 8.1 Properties of Waves Interferance Diffraction
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Petrucci 8.5 Particle-Wave Duality Matter and energy exhibits both wave-like and particle-like properties The wavelength of matter is called the "‘de Broglie wavelength"’ λ = h p = h mu Electron Baseball m 9 . 1 × 10 - 31 kg 0.10 kg v 1 × 10 7 m/s 35 m/s λ = h mu 7 × 10 - 11 m 2 × 10 - 34 m Atomic sizes << atom De Broglie Wavelength The wavelength of matter is called the "‘de Broglie wavelength"’ λ = h p = h mu Electron Baseball m 9 . 1 × 10 - 31 kg 0.10 kg v 1 × 10 7 m/s 35 m/s λ = h mu 7 × 10 - 11 m 2 × 10 - 34 m Atomic sizes << atom Is It a Wave???? Is It a Particle???? The de Broglie relationship assigns wave properties to particles and particle prop- erties to waves! Does this mean that particles convert into waves and back? 2
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It’s neither a circle nor a triangle, but what you see depends on the type of experi- ment! Petrucci 8.1, 8.3 Light Electromagnetic wave of oscillating electric and magnetic fields that in vac- uum travels at the speed of light, c = 3 . 0 × 10 8 m/s Stream of particles ( Photons ) each with energy E = Planck’s constant, h = 6 . 63 × 10 - 34 Js Frequency ν = c λ (unit s - 1 = Hz) Electromagnetic Spectrum White light consists of all colors Dispersing light though a prism splits it into its spectral components 3
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7 . 5 × 10 14 s - 1 4 . 3 × 10 14 s - 1 Petrucci 8.2 Atomic Spectra Spectra of geseous atoms consists of dis- crete lines (only specific frequencies) Electrons can only have discrete energies Transition between two discrete energy levels involves an energy change, Δ E = E 2 - E 1 Conservation of energy then requires absorption or emission of photon with matching energy = Δ E Petrucci 8.4 The Bohr Atom Niels Bohr made a semi classical model that successfully explained the ex- perimentally observed lines in the hydrogen atom "‘Quantized Planetary Model"’ 4
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E n = R H n 2 n = 1 , 2 , 3 , ··· R H = 2 . 179 × 10 - 18 J n is the angular quantum number The higher n , the further away from the nucleus Example 1: The Bohr Atom 1. Would a transition from energy level n = 7 to n = 3 require absorption or emission of a photon? 2. What would be the wavelength of the photon for the above transition?
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This note was uploaded on 12/04/2009 for the course CHE 15940 taught by Professor Madsen during the Spring '09 term at UC Davis.

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reader5 - Electrons in Atoms Rutherford atom Electrons are...

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