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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. H 1s1 O 1s2 2s2 2p4**

Gives 2 H’s with no e- and O with full octet. 1s ___ 1s ___ 2s ___ 2p ___ ___ ___

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We Get H 1s1 O 1s2 2s2 2p4 Gives 2 H’s with no e- and O with full octet. 1s ___ 1s ___ 2s ___ 2p ___ ___ ___

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Hybridization Process that changes properties of valence electrons by mixing atomic orbitals to form special orbitals for bonding 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 AO’s 4. All bonded atoms hybridize

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WHEN ATOMS BOND atomic orbital hybrid orbital

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**All hybrid orbitals of an atom are said to be DEGENERATE**

(of equal energy)

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CH4 C: AO 2p __ __ __ s ____ H C H H H

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CH MO __ __ __ __ H C H H H sp3 hybrid orbitals

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**4 Items Equally Distributed**

sp3 hybridization sp3 hybrid orbitals tetrahedral species sp3 shape tetragonal 4 Items Equally Distributed

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Tetragonal

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**C C H H H H H H H H Lewis Structure Electron Pair Geometry**

Molecular Model C H H H H C H H H

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**InCl3 In: AO 5p __ __ __ 5s _____**

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InCl MO __ __ __ Cl In 5p __ Cl Cl sp2 hybrid orbitals

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**trigonal planar species 3 Items Equally Distributed**

sp2 hybridization sp2 hybrid trigonal planar species sp2 shape 3 Items Equally Distributed

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BaCl2 Cl - Ba - Cl Ba: AO 6p ___ ___ ___ s _____

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**BaCl2 Cl - Ba - Cl Ba: MO 6p ___ ___**

sp hybrid orbitals

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**2 Items Equally Distributed**

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

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**PF5 P: AO 3d ___ ___ ___ ___ ___ 3p ___ ___ ___ 3s ____**

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PF5 P: MO 3d ___ ___ ___ ___ ___ ___ ___ ___ ___ sp3d hybrid orbitals

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**5 Items Equally Distributed**

sp3d hybridization sp3d shape trigonal bipyramid species 5 Items Equally Distributed

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**SF6 S: AO 3d ___ ___ ___ ___ ___ 3p _____ ___ ___ 3s _____**

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**SF6 S: MO 3d ___ ___ ___ ___ ___ ___ ___ ___ ___**

sp3d2 hybrid orbitals

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**6 Items Equally Distributed**

sp3d2 hybridization sp3d2 shape octahedral species 6 Items Equally Distributed

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Multiple Bonds sigma bonds () pi bonds ()

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**EXAMPLES O2 2 p-orbitals touching end to end sigma - σ**

O 1s2 2s2 2p p4 2s2 1s2 O 2 p-orbitals touching end to end sigma - σ 2p-electrons reaching over and under pi - π 2s ___ 2p ___ ___ ___ 2p ___ ___ ___ 2s ___ ___ ___

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**Valence Bond Theory Multiple Bond Examples**

C2H4 (ethylene) s (sp3 hybridization) p ( bonding) both

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EXAMPLES C2H2

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EXAMPLES CH3COOH

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**MOLECULAR ORBITAL MODEL**

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

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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 Schrodinger’s equation, and that they are called**

wave-functions

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1s wavefunction r

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- + Negative here Positive 2pz wavefunction

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2pz orbital - + 1s 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**

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 1sA 1sB B A A sigma, s, bonding orbital

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. + - minus 1sA 1sB B A A sigma star, s*, anti-bonding orbital

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**The work on molecular orbitals can be generalized to**

p-orbitals.

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2pz s2p A s2p bonding orbital

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2pz s2p* A s2p* antibonding orbital

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plus A B 2py p2p A p2p bonding orbital

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minus A B 2py p2p* A p2p* 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 have the right symmetry

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plus 2pz 2pz 2py 2py 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

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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

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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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**Molecular Orbital Diagrams**

Bond Order

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**Examine some homonuclear diatomic molecules**

Hydrogen Helium

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s2s* 1sA 1sB s2s

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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 2px 2py 2pz s1s s1s* s2s s2s* s2p p2p s2p* p2p* fluorine gas

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1s 2s 2px 2py 2pz s1s s1s* s2s s2s* s2p p2p s2p* p2p* oxygen gas

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**Using MO Theory, molecules have an electron configuration**

Oxygen gas (s1s)2(s1s*)2 (s2s)2(s2s*)2 (p2py)2 (p2py*)2 (s2pz)2 (p2px)2

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**nitrogen gas 1s 2s 2px 2py 2pz s1s s1s* s2s s2s* s2p p2p s2p* p2p***

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**

C6H6 Lewis Structure

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C2H4 + Br2 C2H4Br2 C6H6 + Br2 NR

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s bonds in benzene p bonds in benzene benzene

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Isomerism 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

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

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**Metals & Semiconductors**

Read pg Study Figures 1-23 Know Insulators Conductors, Semiconductors – intrinsic, extrinsic Dopants

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