lecture 13 - Why does [Cr(NH 3 ) 6 ] 3+ have two...

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Unformatted text preview: Why does [Cr(NH 3 ) 6 ] 3+ have two absorptions for the e g * t 2g transition? A standard spectroscopy problem To answer the question The actual physical movement of an electron from one orbital to another will be affected by the distance the electron has to move to get to the new orbital and any electronic repulsions it encounters along the way d z 2 ( e g *) d xy (t 2g ) is far and encounters many repulsion (higher energy for the transition) d z 2 ( e g *) d xz (t 2g ) is not so far and fewer repulsions Electron-electron repulsion d 2 ion e g t 2g xy xz yz z 2 x 2-y 2 e g t 2g xy xz yz z 2 x 2-y 2 xz + z 2 xy + z 2 lobes overlap, large electron repulsion lobes far apart, small electron repulsion x z x z y y These two electron configurations do not have the same energy How to classify different types of transitions within e g * t 2g d orbital electrons differ in quantum number; l = 2, m l = +2, +1, 0 , 1, or 2; s = In fact, picking an m l value and a spin state is sufficient to specify a particular electronic state: 2 + means a spin-up electron in the m l = 2 orbital More than one d electron But one electron cases are dull no electronic repulsion With more than one electron, Hunds Rule (no two electrons on an atom can share the same quantum numbers) kicks in For d 2 configurations, use ordered pairs to specify electronic states: (2 + , 2 ) or (1 , 1 ) to give two examples these are called microstates Microstates So a microstate is a snapshot description of the complete quantum state of an atoms valence electrons. Define M L as the total angular momentum quantum number for all the valence electrons and S as the total spin of all the valence electrons. Thus, for the microstate (2 + , 2 ), M L = 2 + 2 = 4 and S = +1/2 1/2 = 0 Why microstates?...
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This note was uploaded on 01/19/2012 for the course CHEM 312 taught by Professor Staff during the Summer '08 term at University of Washington.

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lecture 13 - Why does [Cr(NH 3 ) 6 ] 3+ have two...

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