Lecture-16 - Chem111 Fall, 2005 Lecture 16: Bonding and...

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Chem111 Fall, 2005 51 Diatomics Æ pretty straightforward molecular orbitals But how do we deal with more than 2 atoms? In particular, how do we link up the electron configuration with the geometry? Consider CH 4 … electron configuration of C: 1s 2 2s 2 2p 2 ok, so it looks like we should get 2 H's bound at 90 o angles to one another, and the other two H's interact with the spherical 2s orbitals Now, look at a VSEPR treatment: The steric number is 4, and there are four atoms bound, so it must be tetrahedral in shape. Experimentally, we know it has 4 equivalent bonds and that it is tetrahedral. How do we reconcile the two pictures? Two general procedures: 1. Valence Bond Method look at overlap of orbitals in a localized manner eventually gets us to hybrid orbitals 2. Molecular Orbital Method consider the molecule as a whole, with delocalized MOs (e.g. spread over the whole molecule) construct MOs from AOs (LCAO-MO) Lecture 16: Bonding and Molecules Molecular Orbitals (II) hybrid orbitals more than 2 atoms
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Chem111 Fall, 2005 52 Hybrid Orbitals ( Å Valence bond theory) H:Be:H has a similar problem as CH 4 Æ VSEPR and experiment show this molecule is linear Æ the e- config. of Be is 1s 2 2s 2 Æ but wait … how can we form any bonds at all? the Be doesn't have any open spaces, really, as its configuration is 1s 2 2s 2 !
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This note was uploaded on 02/08/2010 for the course CHEM 111 taught by Professor Kenney during the Spring '08 term at Case Western.

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Lecture-16 - Chem111 Fall, 2005 Lecture 16: Bonding and...

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