Chapter 12.1-12.3 CHEM 1B
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This 6 page Class Notes was uploaded by Stacy Vargas on Thursday October 1, 2015. The Class Notes belongs to CHEM 1B at University of California - Santa Cruz taught by Roberto Bogomolni in Fall 2015. Since its upload, it has received 87 views. For similar materials see CHEM 1B in Chemistry at University of California - Santa Cruz.
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Date Created: 10/01/15
Chapter 12 Quantum Mechanics and Ammig Theory 121 Electroma netic Radiation Electromagnetic Radiation ER is one of the ways energy travels This type of radiation has this name because electrical and magnetic elds simultaneously oscillate in planes mutually perpendicular to each other Characteristics of waves wavelength frequency and speed is the distance between 2 consecutive peaks or troughs in a waveas shown in the image below it is represented in the Greek letter lambda A o The units of wavelength will always be nanometers nm or meters m 4 III 1 seminal quot 1 E El m 1 399 r Q 5 Ci l IE 339 393 El H TIN ws 8 cyclesfsem nd 8 hart iii 16 cyclesilseconstl 1in hertz is the number of waves or cycles per second and is represented by the Greek letter nu o The units used for frequency is hertz hz All types of ER travel at the speed of light however shortwavelength radiation has the highest frequency In the equation above c represents the speed of light which will be de ned as 299 x 10 8 ms A is your wavelength which is in meters and v is your frequency The image below shows the classi cation of ER Radiation provides important means of energy transfer Wavelength in meters 10 10 qu4gtltl f39gtlt10f lofl 10f I lit2 inf l quot l R l l i F 1 V n Gamma litrtmellet llnl fared lull1ettiill39En39ee Realme rays raft x 39 PM Simttweve HM Size of r i r 4 b Q I C I Iquot I tremie g 7 nuclei Merrie Meleeulee Peper elip midi311 l 4x10 SXlni mumT fxlni 122 The nature of matter The term blackbody is used in this context to depict that radiation originates from thermal energy of the body only 0 Doesn t include radiation re ected from the object amp doesn t depend on the material composing the object Blackbody radiation is closely approximated by the radiation emitted through a tiny hole from a cavity inside an object t v ZUDG intenailty i U U U 3008 5001 Wavelength 11111 Figure MA The prefiie e39f radiatien emitted trim a blaekbedly Nate tlhat the maximum slhifta te shatter wavelengths as the temperature ie increased in agreement with the elbsewed Change from a reddieh to a white QIOW ae iren is heated te higher temperatures a classical theory of matter that predicts a radiation pro le that has no maximum and goes to in nite intensity at very short wavelengths is represented by h and has the value of 6626 x 10quot 34 Joules J s The change in energy AE is represented by the equation where n is an integer h is Planck s constant and v is the frequency of the ER absorbed or emitted small quotpacketsquot of energy that can be transferred only in discrete units of size hv stream of quotparticlesquot viewed in ER Energy of each photon is expressed in the following equation A i be Epheteh where h is Planck s constant v is the frequency of the radiation and A is the wavelength of the radiation when electrons emit from the surface of a metal when light strikes it Characteristics of Photoelectric effect 1 2 3 4 No electrons are emitted by a given metal below a speci c frequency vO Light with frequency lower than threshold frequency no electrons are emitted regardless of the intensity of the light Light with frequency greater than threshold frequency the of electrons emitted increases with the intensity of the light Light with frequency greater than threshold frequency the kinetic energy of the emitted electrons increases linearly with the frequency of the light Minimum energy required to remove electron EO hvO because a photon with less energy than EO vltv0 can t remove an electron light with frequency less than the threshold frequency produces no electrons Light where vgtvO the energy in excess of that required to remove electron is given to the electron as kinetic energy KE KEeleeteen myz kiwi fl i i R Meesef Veleeity Energny Energy required eleetren if ineicient ten remeveeleetren elleetren pheten frern metel s enifeee A greater intensity means that more photons are available to release electrons To represent the relationship between mass and energy Einstein rearranged the famous E mcquot2 equation to the following Energyr 2 v C l R Meee Speed elf light Mass is a form of energy mass and however a typical no Light a wave phettettteeee 000 00 Light as etreem et pheteme Figure 126 Electrerneginetie retzlietien vexhieite wetre prepertiee and particulate prep ertiee The energy let each phe ten ef the radiation ie related te the wave length and frequency by the ecttiietien EWW he heft Photons do not exhibit are not affected by gravity photon is in no sense a particle Photon has mass in a relativistic sense it has rest mass
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