CHEM 1211 Lecture 15 Outline of Last Lecture I Hess s law continued II Chapter 6 Atoms Electronic Structure III Color in Neon Lights Fireworks etc A Properties of Light photon IV Constant Frequency Variable Wavelength A Photoelectric Effect B Light Energy Outline of Current Lecture I Electromagnetic Radiation A Emission Spectrum B Absorption Spectrum C Bohr Model of Atom II Predicting Emission Lines of Hydrogen A Rydberg Equation III Electronic Transitions A Wave nature of electrons Current Lecture I Electromagnetic Radiation A Emission Spectrum formed by electric current passing through a gas in a vacuum tube at a very low pressure which causes gas to emit light Ex Prism Light Prism Detector If we add lots of energy to a sample of elemental gas we get an emission spectrum elemental specific 1 In the hydrogen emission spectrum a band is observed at 4860A What is the frequency and energy of this emission line C v V C 4860A 1 x 10 10m 4 860 x 10 7m 1A V visible green light 3 00 x 108 m s 6 17 x 1014 s 1 nHz 4 860 x 10 7m II III E hv E 6 626 x 10 34 J s 6 17 x 108 m s 4 088 x 10 19 J photon 4 088 x 10 19 J 6 02 x 1023 2 46 x 105 J mol photon photon Mol photon E 246 KJ mol photon B Absorption Spectrum shine a bean of white light through gas Indicates wavelengths of light that have been ABSORBED C Bohr Model of Atom only works for hydrogen explains atomic spectra Energy of quantized state RhC n2 N integral numbers only 1 to infinity Radius of orbitals n2 0 0529nm Predicting Emission Lines of Hydrogen A Rydberg Equation 1 RH 1 1 n12 n22 RH 1 097 x 107 m 1 RH 1 097 x 10 2 nm 1 n refers to one of the infinite possible energy state of the electron in hydrogen requirement n1 n2 Electronic Transitions 1 Move an electron from a lower energy level to a higher energy level E RhC 1 1 n12 n22 2 Start a rotational mode of motion 3 Begin a vibrations mode of motion 4 Gain kinetic energy translational motion ex water A Wave nature of electrons 2 r n DE Broglie said the wavelength of an object h mv 2 r nh mv Angular momentum mvr nh 2
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