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Chapter 8 Notes - CHAPTER 8 ELECTRONS IN ATOMS...

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CHAPTER 8 ELECTRONS IN ATOMS 8.1)Electromagnetic Radiation a) Electromagnetic Radiation : A form of energy transmission in which electric and magnetic field are propagated as waves. b) Wave : A disturbance that transmits energy through space or a material medium. c) Waves consist of crests and toughs. d) Amplitude : Maximum height of the wave above the center line. e) Wavelength: Distance between the tops of two successive crests. Designated by λ. f) Frequency : Number of crests or troughs that pass through a given point per unit of time, designated by ν. g) Electromagnetic radiation is produced by an accelerating electrically charged particle. h) FREQUENCY, WAVELENGTH, AND SPEED OF ELECTROMAGNETIC RADIATION 1) Hertz (Hz) : SI unit for frequency. 2) Speed of light : Has a constant value in a vacuum, with speed . × 2 997925 108ms 3) = × c ν λ 4) Electromagnetic Spectrum i) AN IMPORTANT CHARACTERISTIC OF ELECTROMAGNETIC WAVES 1) In phase : Where waves’ crests and troughs coincide when they meet. They combine to form higher crests and deepest troughs. 2) Constructive Interference : Addition of waves in phase. 3) Out of Phase : Waves that are out of step. 4) Destructive Interference : Cancellation of waves.
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5) White light contains all the colors of the rainbow. 6) Diffraction : The dispersion of different wavelength components of a light beam through the interference produced by reflection from a grooved surface. j) THE VISIBLE SPECTRUM 1) The speed of light is lower in any medium than it is in a vacuum. 2) When a beam of white light is passed through a transparent medium, wavelength components are refracted differently and the light is dispersed into a band of colors ( spectrum) 8.2)Atomic Spectra a) Continuous spectrum vs. Discontinuous spectrum. (continuous is when there are many wavelength components) b) Atomic, or line, spectra : Discontinuous spectra. c) Each element has its own distinctive line spectrum. d) Robert Bunsen and Gustav Kirchhoff developed first spectroscope. e) Balmer’s equation for wavelength of the lines in the spectral line of hydrogen. 5) = . × - - ν 3 2881 1015s 1122 1n2 6) For n as an integer greater than two. 8.3)Quantum Theory a) Classical physics couldn’t provide a complete explanation of light emission by heated solids. b) Blackbody Radiation : Light emission by heated solids. c) In 1900, Max Planck proposes: Energy, like matter, is discontinuous . d) Quantum of Energy : The difference between any two allowed energies of a system. e) = ε nhν f) = , = , = , ε energy n positive integer ν oscillator frequency = . h constant
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g) Planck’s Constant : = . - h 6 62607 x 10 34 J s h) Planck’s equation : E = h ν i) THE PHOTOELECTRIC EFFECT 1) Photoelectric effect : When light strikes the surface of certain metals, electrons are ejected. 2) Discovered by Heinrich Hertz in 1888. 3) Electron emission only occurs when the frequency of the incident light exceeds a particular threshold frequency (ν 0 ) 4) Number of electrons emitted depends on the intensity of the incident light.
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