Sep 19 - Exam 1 Monday Chapters 7-10 Grotrian Diagrams...

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Exam 1 Monday September 26, 2016 Chapters 7-10
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PHYSICAL CHEMISTRY: QUANTA, MATTER, AND CHANGE 2E| PETER ATKINS| JULIO DE PAULA | RONALD FRIEDMAN ©2014 W. H. FREEMAN D COMPANY Grotrian Diagrams Notice: Most of the spectroscopic transitions are between p orbitals and s orbitals, and there are no transitions between s orbitals
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Why does the Grotrian diagram look like this? Recall, For the hydrogen atom and other one-electron atoms: The selection rules are l = ±1, m l = 0, ±1 Transitions between s orbitals are forbidden for hydrogen atoms because all s orbitals have l = 0 so this would violate the selection rules!! The selection rules mandate that allowed transitions must be accompanied by precisely 1 quantum of change in total orbital angular momentum l . So, because the first law of thermodynamics tells us that energy must be conserved, we conclude that 1 photon = 1 quantum of angular momentum
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Atomic Spectroscopy of He Ground State Configuration 1s 2 Even though chemists cannot use the Schrodinger Equation to exactly solve the orbitals and energies of He atoms, spectroscopists can precisely measure the energy differences between the orbitals!
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Atomic Spectroscopy of Helium—spectroscopic evidence for Hund's rule of maximum spin multiplicity The lowest possible excited state configuration of He is 1s 1 2s 1 Notice that there are multiple ways to load two electrons into this configuration, since they are not paired and not subject to the Pauli principle The possibilities for the spin parts of the wavefunctions are: (1) (2) S (1) (2) S (1/2) 1/2 { (1) (2) + (1) (2) S (1/2) 1/2 { (1) (2) - (1) (2) A We call these a singlet state and a triplet of states, sometimes or simply a triplet configuration. The term "triplet state" is also frequently seen, but strictly speaking, is incorrect. It is actually a triplet of three different states, which are energetically degenerate in the absence of an applied electromagnetic field. The spin function with symmetry A corresponds to the singlet state The spin functions with symmetry S correspond to the triplet of states
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PHYSICAL CHEMISTRY: QUANTA, MATTER, AND CHANGE 2E| PETER ATKINS| JULIO DE PAULA | RONALD FRIEDMAN ©2014 W. H. FREEMAN D COMPANY
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