Chapter+07_08_QuantumMechanics_PeriodicProperties

Chapter+07_08_QuantumMechanics_PeriodicProperties - CHAPTER...

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CHAPTER 7 & 8 Quantum Mechanics and Periodic Properties of Elements 1 Electromagnetic radiation Energy can be transferred as Work Heat Electromagnetic radiation 2 Visible light Ultraviolet light Infrared light rays X rays Microwaves Electromagnetic radiation A wave is an oscillation that moves outward from a disturbance. 3 Electromagnetic radiation The result is a series of perpendicular oscillating electric and magnetic pulses. All electromagnetic waves travel at the speed of light (c = 2.99792 x 10 8 m/s) in a vacuum. 4 source Description of Electromagnetic Radiation Wavelength (  distance between two neighboring peaks. Measured in units of distance such as m,cm, nm , Å . 1 Å = 1 x 10 -10 m = 1 x 10 -8 cm; 1 nm = 10 -9 m 5 Description of Electromagnetic Radiation Frequency requency (  the Greek letter nu ) is the number of crests or troughs that pass a given point per second. Measured in units of 1/time 6 Measured in units of 1/time s -1 (Hz), min -1 , etc.
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Description of Electromagnetic Radiation Frequency and wavelength of a wave are inversely related to each other. velocity of a wave =   7 For electromagnetic radiation: c =   Electromagnetic Radiation Example : What is the frequency of green light of wavelength 5200 Å? 8 Color the color of light is determined by its wavelength or frequency white light is a mixture of all the colors of visible ligh Tro, Chemistry: A Molecular Approach 9 light a spectrum R ed O range Y ellow G reen B lue V iolet (Roy G BIV) when an object absorbs some of the wavelengths of white light while reflecting others, it appears colored the observed color is predominantly the colors reflected Electromagnetic Spectrum Tro, Chemistry: A Molecular Approach 10 Particle Nature of Electromagnetic Waves Blackbody radiation is the energy emitted by an object when heated. Max Planck explained it 11 Max Planck explained it by assuming that energy can be gained or lost only in integral multiples of a smallest unit of energy called quantum . The Photoelectric Effect Light can strike the surface of some metals causing electrons to be ejected. 12
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Particle Nature of Electromagnetic Waves To explain the photoelectric effect, Einstein proposed that electromagnetic radiation can be viewed as a stream of tiny packets of energy called photons . ( Energy is quantized .) 13 The energy of one photon is proportional to the frequency of the electromagnetic wave: E = h where h is Planck’s constant, 6.63 10 34 J-s. Ejected Electrons 1 photon at the threshold frequency has just enough energy for an electron to escape the atom binding energy, Tro, Chemistry: A Molecular Approach 14 for higher frequencies, the electron absorbs more energy than is necessary to escape this excess energy becomes kinetic energy of the ejected electron Kinetic Energy = E photon –E binding KE = h - Electromagnetic Radiation Example
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Chapter+07_08_QuantumMechanics_PeriodicProperties - CHAPTER...

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