Unit2Day2 Crawford Monday September 23 2013 4 15 PM Vanden Bout LaBrake Crawford CH301 Why are there no blue fireworks LIGHT ELECTRONS QUANTUM MODEL UNIT 2 Day 2 CH302 Vanden Bout LaBrake Fall 2013 Important Information EXAM GRADES WERE GREAT EXAM WRAPPER QUEST LM BONUS POINTS LM12 13 due today 9AM HW04 due today 9AM LM14 15 16 due Th 9AM Laude Lecture 2 3 LMs CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 1 What are we going to learn today The simplest Atom Hydrogen Understand how light can probe electrons in atoms Recognize that electrons have discrete energy levels in atoms Predict the energy for transitions of an electron between the energy levels in hydrogen Relate the empirical model to the theoretical model of the energy levels of electrons in H atom Solutions to the theoretical model predict electron configuration CH301 Vanden Bout LaBrake Fall 2013 QUIZ CLICKER QUESTION 1 What is the energy associated with a photon that has a wavelength of 550 nm Plank s constant 6 626 X 10 34 J s Speed of light 2 99 x 108 m s A 414 kJ B 3 61 x 10 37 J C 3 61 X 10 19 J D 235 J E 4 14 J CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 2 QUIZ CLICKER QUESTION 2 The Rydberg formula is an empirically derived relationship between the difference between the inverse square of integer values and emission spectral lines A True B False CH301 Vanden Bout LaBrake Fall 2013 Exciting Electrons Demo CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 3 Exciting Electrons Demo CH301 Vanden Bout LaBrake Fall 2013 Exciting Electrons Demo Add electrical energy to various elements Describe results CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 4 Exciting Electrons Demo CH301 Vanden Bout LaBrake Fall 2013 Exciting Electrons Demo Think Like a Chemist H H H H H H H H Ne Ne Ne Ne CH301 Vanden Bout LaBrake Fall 2013 POLLING CLICKER QUESTION 3 Exciting Electrons Demo WHICH SPECTRUM WOULD YOU EXPECT TO SEE IF WE WERE TO PUT A GRATING BETWEEN YOU AND THE LIGHT SOURCE A Unit2Day2 Crawford Page 5 Exciting Electrons Demo WHICH SPECTRUM WOULD YOU EXPECT TO SEE IF WE WERE TO PUT A GRATING BETWEEN YOU AND THE LIGHT SOURCE A B CH301 Vanden Bout LaBrake Fall 2013 POLL CLICKER QUESTION 4 Exciting which gas leads to emission of the the highest energy visible photons a He b H2 c Ne CH301 Vanden Bout LaBrake Fall 2013 E is proportional to 1 n2 Where do these Energy levels come from Unit2Day2 Crawford Page 6 Where do these Energy levels come from CH301 Vanden Bout LaBrake Fall 2013 CH301 Vanden Bout LaBrake Fall 2013 Rydberg Formula Mathematician Balmer noted a pattern in the frequencies of some of the lines Rydberg figured this out with an Empirical model for all the lines for the H atom simple because there is only one electron Convert wavelength to frequency to energy n1 and n2 are Integers CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 7 Rydberg Formula Discrete lines Discrete Energies Particular wavelengths correspond to transitions between different energy levels NOT ALL ENERGIES ARE POSSIBLE What is the energy difference between the n 1 and n 2 states Negative corresponds to emission Positive to absorption n1 and n2 are Integers CH301 Vanden Bout LaBrake Fall 2013 THIS INTERPRETATION OF THE LINE SPECTRA ALLOWED SUGGESTED THAT THE ENERGIES OF THE ELECTRONS MUST BE QUANTIZED CH301 Vanden Bout LaBrake Fall 2013 Bohr s model solar system EMPIRICAL Unit2Day2 Crawford Page 8 Bohr s theory allowed for the calculation of an energy level Or the calculation of the emitted wavelength upon release of energy when an electron transitions from higher to lower energy E h c CH301 Vanden Bout LaBrake Fall 2013 BOHR MODEL Bohr model was not working well for an atom with more than one electron It treated the electron as a particle de Broglie had shown that electrons have wave properties Schr dinger decided to emphasize the wave nature of electrons in an effort to define a theory to explain the architecture of an atom http upload wikimedia org wikipedia commons c cf Circular Standing Wave gif CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 9 Wave Particle Duality Small low mass particles have wave like properties They are neither described as particles or waves They have characteristics of each We saw the same issue for light Seems like a wave but the energy photon appears particle like CH301 Vanden Bout LaBrake Fall 2013 How do we deal with the new wave particle things We need a new model Quantum Mechanics It doesn t make sense It shouldn t You don t live in a world of tiny particles with vanishingly small mass and momentum It is what it is CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 10 The Schr dinger Equation allows us to solve for all possible wavefunctions and energies Wave functions Tell us about where the electron is the probability of finding the particle at a given position Energies Tell us about the energy of the electron CH301 Vanden Bout LaBrake Fall 2013 The Hydrogen Atom Simplest of all atomic problems 1 proton 1 electron Function Machine Schr dinger Equation That will give us the solutions Put that into the Schr dinger Equation and solve Wavefunctions and energies CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 11 The Hydrogen Atom Function Machine Schr dinger Equation That will give us the solutions Infinite number of solutions Which solution are we are interested in LOWEST ENERGY GROUND STATE ELECTRON CONFIGURATION CH301 Vanden Bout LaBrake Fall 2013 Where is the Energy Two key ideas from Quantum Mechanics systems are described by Energies Tell us about the energy of the electron CH301 Vanden Bout LaBrake Fall 2013 DIAGRAM SOLUTIONS LOWEST ENERGY ELECTRON TO HIGHEST ENERGY ELECTRON Draw energy level diagram for hydrogen atom Unit2Day2 Crawford Page 12 CH301 Vanden Bout LaBrake Fall 2013 ENERGY Rydberg from Bohr model R 1 n12 1 n22 R 3 29 X 1015 Hz Schr dinger calculated actual energy of the e in H using his wave equation with the proper expression for potential energy En hR n2 2 18 x 10 18 J n2 n is principal quantum number which is an integer that labels the different energy levels e will climb up the energy levels until freedom ionization n CH301 Vanden Bout LaBrake Fall 2013 Unit2Day2 Crawford Page 13 Exciting Electrons Demo SUMMARIZE THE SIMILARITIES AND DIFFERENCES BETWEEN THE PHOTOELECTRIC EFFECT AND THE EMISSION SPECTRA OF EXCITED ELEMENTS CH301 Vanden Bout LaBrake Fall 2013 Where is the particle Two key ideas from
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