# apchp7Kotz - 11/21/2011 Topics: Atomic Structure 7.1...

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11/21/2011 1 Atomic Structure Topics: 7.1 Electromagnetic Radiation 7.2 Planck, Einstein, Energy, and Photons 7.3 Atomic Line Spectra and Niels Bohr 7.4 The Wave Properties of the Electron 7.5 Quantum Mechanical View of the Atom 7.6 The Shapes of Atomic Orbitals 7.7 Atomic Orbitals and Chemistry Properties of an electromagnetic wave Node General Transverse Wave Properties 2.99792458x10 8 m/s (or Hz or 1/s) Standing Waves Two or more points of zero amplitude Distance between consecutive nodes = /2 Standing waves must have a distance between fixed ends = n( /2), where n is an integer.

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11/21/2011 2 Example Problem (7.1): The line shown here is 10cm long: a) Draw a standing wave with one node between the ends. What is the wavelength of this wave? b) Draw a standing wave with three evenly spaced nodes between the ends. What is its wavelength? c) If the wavelength of the standing wave is 2.5cm, how many waves fit within the boundaries? How many nodes are there between the ends? 0 5 10 a) 10cm b) 5cm c) 10/2.5 = 4 waves; 7 nodes Electromagnetic radiation is self-propagating (i.e. it doesn’t require a medium to travel through. It can travel through the vacuum of space.) Example Problem (7.2): a) Which color in the visible spectrum (ROY-G-BIV) has the highest frequency? Which has the lowest frequency? b) Is the frequency of the radiation used in a microwave oven higher or lower than that from a FM radio station broadcasting at 91.7MHz? c) Is the wavelength of x-rays longer or shorter than that of ultraviolet light? Answers: a) Blue/violet has the highest frequency. Red has the lowest frequency (longest wavelength). b) Microwaves are higher in frequency (shorter wavelength) than FM station 91.7MHz. c) X-ray wavelengths are shorter (higher frequency) than that of UV light. Blackbody Radiator Blackbody Curves This is where the ultraviolet catastrophe occurred. Traditional Theories: Intensity of radiation should increase continuously with decreasing wavelength http://amazing-space.stsci.edu/resources/explorations/light/index.html http://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html Classical theory (dotted lines) based on the Raleigh-Jeans Law, which caused the ultraviolet catastrophe. The “Planck” curves are given in red and blue and result from the quantized energy nature of light. Max Planck (1900): Vibrations in atoms are quantized (i.e. Only certain vibrations with certain frequencies are allowed) 6.6260693x10 -34 Js
11/21/2011 3 The Photoelectric Effect Assumption: Energy is carried on the amplitude of a wave (as in classical waves). Prediction: Since the amplitude of an EM wave correlates with the brightness of the light, light of high enough intensity irradiating a metal for a long enough period of time should be able to eject electrons from the surface of a metal. Reality: It was the frequency of the light that determined whether or not electrons were ejected regardless of the time of irradiation.

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## This note was uploaded on 12/07/2011 for the course CHEM 100 taught by Professor Feebeck during the Fall '10 term at Purdue University-West Lafayette.

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apchp7Kotz - 11/21/2011 Topics: Atomic Structure 7.1...

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