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AP Notes Chapter 9 Hybridization and the Localized Electron Model Valence Bond Theory Molecular Orbital Theory Metals & Semiconductors

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Hybridization and the Localized Electron Model Localized Electron Model developed from Valence Bond Theory

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Why do we need it? Consider the water species. Consider the water species. H 1s 1 H 1s 1 O 1s 2 2s 2 2p 4 O 1s 2 2s 2 2p 4 Gives 2 Hs with no e- and O with full octet. 2s ___2p ___ ___ ___ 2s ___ 2p ___ ___ ___ 1s ___

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We Get H 1s 1 H 1s 1 O 1s 2 2s 2 2p 4 O 1s 2 2s 2 2p 4 Gives 2 Hs with no e- and O with full octet. 2s ___2p ___ ___ ___ 2s ___ 2p ___ ___ ___ 1s ___

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Hybridization Process that changes properties of valence electrons by mixing atomic orbitals to form special orbitals for bonding Process that changes properties of valence electrons by mixing atomic orbitals to form special orbitals for bonding atomic molecular orbitals orbitals AO MO atomic molecular orbitals orbitals AO MO

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Principles 1. Conservation of orbitals 2. Hybrid correlates with molecular geometry 3. Energy level of MO is between that of AOs 4. All bonded atoms hybridize

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atomic orbital hybrid orbital WHEN ATOMS BOND

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All hybrid orbitals of an atom are said to be DEGENERATE (of equal energy)

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CH 4 C: AO 2p __ __ __ 2 s ____ C H H HH

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CH 4 MO __ __ __ __ C H H HH sp 3 hybrid orbitals

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sp 3 hybridization sp 3 hybridsp 3 hybrid orbitals tetrahedral species sp 3 shapesp 3 shape tetragonal 4 Items Equally Distributed

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Tetragonal Tetragonal

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Lewis Structure Electron Pair Geometry Molecular Model H H HH C H H H H C

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InCl 3 In: AO 5p __ __ __ 5s _____ In Cl

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InCl 3 MO __ __ __ __ __ __ In Cl 5p __ sp 2 hybrid orbitals

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sp 2 hybridization sp 2 hybrid trigonal planar species sp 2 shape 3 Items Equally Distributed

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BaCl 2 Cl - Ba - Cl Ba: AO 6p ___ ___ ___ 6s _____

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BaCl 2 Cl - Ba - Cl Ba: MO 6p ___ ___ ___ ___ sp hybrid orbitals

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sp hybridization sp hybrid linear species sp shape 2 Items Equally Distributed

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PF 5 P : AO 3d ___ ___ ___ ___ ___ 3p ___ ___ ___ 3s ____

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PF 5 P : MO 3d ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ sp 3 d hybrid orbitals sp 3 d hybrid orbitals

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sp 3 d hybridization sp 3 d shape trigonal bipyramid species 5 Items Equally Distributed

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SF 6 S: AO 3d ___ ___ ___ ___ ___ 3p _____ ___ ___ 3s _____

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SF 6 S: MO 3d ___ ___ ___ ___ ___ ___ ___ ___ ___ sp 3 d 2 hybrid orbitals

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sp 3 d 2 hybridization sp 3 d 2 shape octahedral species 6 Items Equally Distributed

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Multiple Bonds sigma bonds ( ) pi bonds ( )

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EXAMPLES O 2 O 2 O 1s 2 2s 2 2p 4 2p 4 2s 2 1s 2 O 2 p-orbitals touching end to end sigma - σ 2p-electrons reaching over and under pi - π 2s ___2p ___ ___ ___ 2s ___ 2p ___ ___ ___ 2p ___ ___ ___ 2s ___ ___ ___

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Valence Bond Theory Multiple Bond Examples C 2 H 4 (ethylene) C 2 H 4 (ethylene) (sp 3 hybridization) (sp 3 hybridization) ( bonding) ( bonding) both both both

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EXAMPLES C 2 H 2 C 2 H 2

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EXAMPLES CH 3 COOH CH 3 COOH

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Valence Bond Theory concentrates on individual bonds in a molecule and tends to ignore electrons not used in bonding. MOLECULAR ORBITAL MODEL

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Molecular Orbital Theory assumes ALL the orbitals of the atoms are able to take part in bonding.

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Every atom has a complete set of orbitals, but not all of them contain electrons

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Remember that orbitals are really the solutions of Schrodingers equation, and that they are called wave-functions

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r 1s wavefunction

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2p z wavefunction - + Negative here Positive here

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2p z orbital s orbital

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While wave functions can be positive or negative, probabilities can only be positive.

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Wave functions, like waves, can overlap with one another. They can reinforce each other, or they can cancel each other out.

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plus 1s A 1s B B A A B A sigma,, bonding orbital

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minus 1s A 1s B B A A A sigma star,, anti-bonding orbital - B.

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The work on molecular orbitals can be generalized to p-orbitals.

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2p z 2p A 2p bonding orbital

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2p z 2p A 2p antibonding orbital

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plusA AB B 2p y 2p A 2p bonding orbital

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minus A A B B 2p y 2p A 2p antibonding orbital

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Many combinations of orbitals can produce bonding and anti- bonding molecular orbitals, s with p, d with p, etc.

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Orbitals on the two bonding atoms must meet 2 conditions They must be similar in energy They must be similar in energy They must have the right symmetry They must have the right symmetry

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2p z 2p y plus 2p y 2p z Orbitals pointing in different directions cannot overlap to form molecular orbitals.

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Molecular Orbital Theory 1. Molecular orbitals are made from atomic orbitals 2. Orbitals are conserved 3. Molecular orbitals form in pairs: bonding & antibonding

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Bonding Molecular Orbital Geometry favorable to overlap Geometry favorable to overlap

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When a bonding orbital is formed, the energy of the orbital is lower than those of its parent atomic orbitals.

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Anti-bonding Molecular Orbital Geometry not favorable to overlap Geometry not favorable to overlap

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Similarly, when an anti- bonding orbital is formed, the energy of the orbital is higher than those of its parent atomic orbitals.

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Bond Order Molecular Orbital Diagrams

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Examine some homonuclear diatomic molecules Hydrogen Hydrogen Helium Helium

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1s A 1s B 2s

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Paramagnetic 1. Responds to magnetic field 2. Has unpaired electrons

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Diamagnetic 1. Does not respond to magnetic field 2. All electron paired

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1s 2s 2p x 2p y 2p z 1s 2s 2p fluorine gas

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1s 2s 2p x 2p y 2p z 1s 2s 2p oxygen gas

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Using MO Theory, molecules have an electron configuration Oxygen gas Oxygen gas ( 1s ) 2 ( 1s * ) 2 ( 1s ) 2 ( 1s * ) 2 ( 2s ) 2 ( 2s * ) 2 ( 2s ) 2 ( 2s * ) 2 ( 2py ) 2 ( 2py * ) 2 ( 2py ) 2 ( 2py * ) 2 ( 2pz ) 2 ( 2px ) 2 ( 2pz ) 2 ( 2px ) 2

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1s 2s 2p x 2p y 2p z 1s 2s 2p nitrogen gas Magnet Movie

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Bond Strength Bond Length

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Strengths of Localized Electron Model 1. Simple 2. Easy to understand 3. Predicts geometry of molecule

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Limitations of Localized Electron Model 1. Does not address concept of resonance or unpaired e - 2. Cannot explain color in transition metal compounds

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Strengths of Molecular Orbital Model 1. Better represents actual molecular system 2. Provides basis for explaining properties of molecular systems

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Limitations of Molecular Orbital Model 1. MO diagrams are complex. 2. MO diagrams are difficult for molecules with more than two atoms. 3. No prediction of geometry

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Combining the Localized Electron and Molecular Orbital Models

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Draw the Lewis structure of benzene C 6 H 6 Lewis Structure

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C 2 H 4 + Br 2 C 2 H 4 Br 2 C 6 H 6 + Br 2 NR

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bonds in benzene bonds in benzene benzene

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Isomerism Isomers – two or more compounds with same molecular formula but different arrangements of atoms Isomers – two or more compounds with same molecular formula but different arrangements of atoms Cis – Trans Isomerism (NOT mirror images of each other NOT super imposable. Cis – Trans Isomerism (NOT mirror images of each other NOT super imposable. Cis Trans Cis Trans

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Resonance and MO XX The more resonance structures the more stable the molecule

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Metals & Semiconductors Read pg Read pg Study Figures 1-23 Study Figures 1-23KnowInsulators Conductors, Semiconductors – intrinsic, extrinsic Dopants

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