UT Knoxville CHEM 120 - Chapter 6 Lecture Outline (13 pages)

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1 Chapter 6 Atomic Structure 6 1 The Wave Nature of Light progressive repeating disturbance that spreads through a medium from a point of origin to more distant points there is little movement of the material in the direction of the disturbance WAVES oscillations in electric and magnetic fields that are propagated over distances distance between any two identical points in consecutive cycles height of a wave of wavelengths that pass through a point in a unit of time number of cycles of the wave wavelength frequency speed of the wave c m s wavelength is to frequency 2 amplitude is intensity it does not affect wavelength or frequency EXAMPLE Calculate the frequency of a radio wave that has a wavelength of 4 00 meters Calculate the wavelength of light that has the frequency of 1 x 1016 hertz Calculate the frequency of blue light that has a wavelength of 450 nm Calculate the wavelength in nm of an x ray with a frequency of 5 25 x 1018 s 1 The Electromagnetic Spectrum gamma rays x rays ultraviolet visible infrared microwave TV radio 3 6 2 Photons Energy by the Quantum The wave nature of light does not explain how an object can glow when its temperature increases Max Planck explained it by assuming that energy comes in packets or chunks that are called quanta atoms can absorb or emit electromagnetic energy only in smallest amount of energy is a energy of quantum photon E energy can be absorbed or emitted only as a quantum or as exact multiples of a quantum variations in energy are discontinuous Einstein used this assumption to explain the photoelectric effect 1 electrons are energized by photons 2 electrons escape from atom using E from photon 3 excess photon E KE of the ejected electron He concluded that energy is proportional to frequency E h where h Planck s constant 6 626 10 J s Therefore if one knows the wavelength of light one can calculate the energy in one photon or packet of that light c 4 Practice Problems 1 Calculate the E J of a photon of visible light that