Chem141 Chapter7 notes

Chem141 Chapter7 notes - Wenlong Wu Chem141 7 Quantum...

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Wenlong Wu Chem141 7 Quantum Theory and Atomic Structure 256 7.1 The Nature of Light 257 Electromagnetic radiation: include visible light, xrays microwaves, and radio waves. They consist of energy propagated by means of electric and magnetic fields. Wave Nature of Light 1. Frequency: v or nu, is the number of cycles the wave undergoes per second. s -1 , or hertz, Hz. 2. Wavelength, lambda λ, distance between any point on a wave and same point on the next crest. Or the distance the wave travels during one cycle. In meters or in nanometers. 3. In a vacuum, all electromagnetic radiation is the speed of light constant a. c , 2.997x10^8, or 3.00x10^8. 4. Amplitude: the height of the crest or each wave. This is related to the intensity of radiation, or brightness, higher amplitude is brighter and lower dimmer. 5. Electromagnetic Spectrum: all waves are the SAME speed but differ only in frequency and wavelengths. a. Different wavelengths as different colors, monochromatic, and polychromatic (white) 6. Distinction between Energy and Matter: a. Differences between light and particles. b. Refraction: angles change when change medium. Change in speed causes change in direction. c. Diffraction: wave will bend around an object. d. Interference: when lights pass through two adjacent slits: can be constructive or destructive, in phase or out of phase. Particle Nature of Light: Wave Theory vs Photon Theory Matter and light: 3 phenomena confounded scientists: 1. blackbody radiation: solids begin to glow as heated, as in blackbody radiation. Max Planck: proposed hot glowing objects could emit only certain quantities of energy: a. E = nhv , v is frequency, n is positive integer or quantum number, and h is Planck’s constant, units of J*s: b. h = 6.626x10^-34 J*s c. 2. photoelectric effect: the flow of current when monochromatic lights of sufficient frequency shines on a metal plate, breaks electrons and they flow. a. Confusing features: i. Threshold frequency: a minimum frequency. Wave theory relates light energy to amplitude (intensity), NOT frequency (causes different colors). 1. so wave theory predicts an electron will break free when it absorbs enough energy from any frequency (color) ii. Absence of time lag: electrons flow the instant enough frequency is reached. Wave theory predicts a time lag before energy flow. 3.
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This note was uploaded on 11/03/2008 for the course CHEM 141 taught by Professor Mulfod during the Fall '08 term at Emory.

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Chem141 Chapter7 notes - Wenlong Wu Chem141 7 Quantum...

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