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09.28.2011 - Lecture 10 Chem 260 u 2 pz This Week in...

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Lecture 10 Chem 260 1 1 ! g 1 s ! u * 1 s ! g 2 s ! u * 2 s ! u 2 p x , ! u 2 p y ! g 2 p z ! g * 2 p x , ! g * 2 p y ! u * 2 p z Chem 260/261 Lecture 10 9/28/2011 This Week in Chemistry 260/261 Chapter 6: •Born-Oppenheimer Approximation • Valence Bond Theory • Modifications to Valence Bond Theory bonding through overlap of orbitals ground state, structure properties intuitive •MO based approach ( ad hoc aufbau) , bonding, antibonding and non bonding energy level computational 2 3 Today in Chemistry 260/261 Review Valence Bond Theory • Molecular Orbital Theory • H 2 + Molecular Orbitals • Homonuclear Diatomic Molecules • Hetrogenous and polyatomic treament Next Week in Chemistry 260/261 Spectroscopy! • Interaction with Molecules (chapter 20.1) Chemical bonding 4 How does one solve the Schrödinger equation? Valence Bond Theory - Localized Orbitals Molecular Orbital Theory - Delocalized Orbitals Valence Bond Theory Bond will occur between 2 atoms when: 1. An orbital from one atom occupies the same space as an orbital from the other atom – overlap 2. Total number of electrons in the overlapping orbitals is no more than two 5 6 Note there are four coefficients in h 1 -h 4 which are either +1/2 or -1/2. Equal contribution from each orbital involved Hybrid orbitals (Linear combinations) These mixtures (more formally, linear combinations ) are called hybrid orbitals A linear combination of two functions f and g is given by c 1 f + c 2 g , where c 1 and c 2 are numerical coefficients. Linear combinations that give rise to four equivalent hybrid orbitals Each hybrid orbital has a lobe pointing toward the corner of a tetrahedron sp 3 [ ] [ ] [ ] [ ] z y x z y x z y x z y x p p p s h p p p s h p p p s h p p p s h 2 2 2 2 2 1 2 2 2 2 2 1 2 2 2 2 2 1 2 2 2 2 2 1 4 3 2 1 ! + ! = ! ! + = + ! ! = + + + = The hybridization of N atomic orbitals always results in the formation of N hybrid orbitals. Here the LC are of the SAME atom!
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Lecture 10 Chem 260 2 7 The sp 3 Hybrid Orbitals Coordination is four. 8 Hybridization in Alkenes 120° Linear combinations that give rise to three equivalent hybrid orbitals [ ] 1 1 1 1 2 2 2 2 z y x p p p s He C : p z used in π bond ! ! " # $ $ % & ' ' ( ) * * + , - ' ' ( ) * * + , - = ! ! " # $ $ % & ' ' ( ) * * + , - ' ' ( ) * * + , + = ! ! " # $ $ % & ' ' ( ) * * + , + = y x y x y p p s h p p s h p s h 2 2 1 2 2 3 2 3 1 2 2 1 2 2 3 2 3 1 2 2 1 2 3 1 3 2 1 Normalization factor Coordination is three. C C H H H H Coordination is two. 9 Hybridization in Alkynes C C H H 180° Linear combinations that give rise to two equivalent hybrid orbitals [ ] [ ] z z p s h p s h 2 2 2 1 2 2 2 1 2 1 ! = + = [ ] 1 1 1 1 2 2 2 2 z y x p p p s He C : used in π bond 10 H 2 O with VB theory The hybridization of N atomic orbitals always results in the formation of N hybrid orbitals O H H 104° the bonding in H 2 O with VB theory O-H ° bond is sp 3 + s character 11 Other Hybridizations The hybridization of N atomic orbitals always results in the formation of N hybrid orbitals sp 3 d number shape hybridization 2 linear sp 3 trigonal planar sp 2 4 tetrahedral sp 3 5 trigonal bipryramidal sp 3 d 6 octahedral sp 3 d 2 We can use VB theory to explain VSEPR theory These pure schemes with equal contribution from each orbital are not
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