AP Notes Chapter 9

Hybridization and the Localized Electron Model

Valence Bond Theory

Molecular Orbital Theory

Metals & Semiconductors

Hybridization and the Localized ElectronModel

Localized Electron Model developed fromValence Bond Theory

Why do we need it?Why do we need it?

Consider the water species.Consider the water species. H 1sH 1s11

H 1sH 1s11

O 1sO 1s22 2s 2s22 2p 2p44

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

2s ___2s ___ 2p ___ ___ ___ 2p ___ ___ ___

1s ___1s ___

1s ___1s ___

We GetWe Get

H 1sH 1s11

H 1sH 1s11

O 1sO 1s22 2s 2s22 2p 2p44

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

2s ___2s ___ 2p ___ ___ ___ 2p ___ ___ ___

1s ___1s ___

1s ___1s ___

HybridizationHybridization Process that changes properties of valence Process that changes properties of valence

electrons by mixing atomic orbitals to form electrons by mixing atomic orbitals to form special orbitals for bondingspecial orbitals for bonding

atomic molecularatomic molecularorbitals orbitalsorbitals orbitals AO MO AO MO

PrinciplesPrinciples1. Conservation of orbitals1. Conservation of orbitals

2. Hybrid correlates with2. Hybrid correlates with molecular geometry molecular geometry

3. Energy level of MO is 3. Energy level of MO is between that of AO’sbetween that of AO’s

4. All bonded atoms hybridize4. All bonded atoms hybridize

atomicorbital

hybridorbital

WHEN ATOMS BOND

All hybrid orbitals of an atom are said to be

DEGENERATE (of equal energy)

CHCH44

C: AOC: AO

2p __ __ __ 2p __ __ __

22s ____s ____

CH

H

HH

CHCH44

MOMO

__ __ __ ____ __ __ __

CH

H

HH

sp3 hybrid orbitals

sp3 hybridizationsp3 hybrid orbitals

tetrahedral speciessp3 shape tetragonal

4 Items Equally Distributed

TetragonalTetragonal

Lewis StructureLewis Structure

Electron Pair GeometryElectron Pair Geometry

Molecular ModelMolecular Model

H

H

HH CH

H

HH

C

InClInCl33

In: AOIn: AO

5p __ __ __ 5p __ __ __

5s _____5s _____

In

Cl

ClCl

InClInCl33

MOMO

__ __ ____ __ __

In

Cl

ClCl 5p __

sp2 hybrid orbitals

sp2 hybridizationsp2 hybrid

trigonal planar speciessp2 shape

3 Items Equally Distributed

BaClBaCl22

Cl - Ba - ClCl - Ba - ClBa: AOBa: AO

6p ___ ___ ___6p ___ ___ ___

6s _____6s _____

BaClBaCl22

Cl - Ba - ClCl - Ba - ClBa: Ba: MOMO 6p ___ ___6p ___ ___

___ ______ ___ sp hybrid orbitals

sp hybridizationsp hybrid

linear speciessp shape

2 Items Equally Distributed

PFPF5 5

PP: AO : AO 3d ___ ___ ___ ___ ___3d ___ ___ ___ ___ ___

3p ___ ___ ___3p ___ ___ ___

3s ____3s ____

PFPF5 5

PP: : MOMO3d ___ ___ ___ ___3d ___ ___ ___ ___

___ ___ ___ ___ ___ ___ ___ ___ ___ ___

spsp33d hybrid orbitalsd hybrid orbitals

sp3d hybridizationsp3d shape

trigonal bipyramid species

5 Items Equally Distributed

SFSF66

S: AO S: AO 3d ___ ___ ___ ___ ___3d ___ ___ ___ ___ ___

3p _____ ___ ___3p _____ ___ ___

3s _____3s _____

SFSF66

S: S: MOMO 3d ___ ___ ___3d ___ ___ ___

___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___ ___

sp3d2 hybrid orbitals

sp3d2 hybridizationsp3d2 shape

octahedral species

6 Items Equally Distributed

Multiple BondsMultiple Bonds

sigma bonds (sigma bonds ())

pi bonds (pi bonds ())

EXAMPLESEXAMPLESOO2 2

O O 1s1s22 2s 2s22 2p 2p4 4 2p2p4 4 2s2s2 2 1s1s22 OO

2 p-orbitals touching end to end sigma - 2 p-orbitals touching end to end sigma - σσ

2p-electrons reaching over and under pi - 2p-electrons reaching over and under pi - ππ

2s ___2s ___ 2p ___ ___ ___ 2p ___ ___ ___ 2p ___ ___ ___ 2s ___ 2p ___ ___ ___ 2s ___

___ ___ ___ ___

Valence Bond Theory Valence Bond Theory Multiple Bond Multiple Bond

ExamplesExamplesCC22HH4 4 (ethylene) (ethylene) (sp(sp33 hybridization)hybridization)

(( bonding) bonding) bothboth

EXAMPLESEXAMPLESCC22HH2 2

EXAMPLESEXAMPLESCHCH33COOHCOOH

Valence Bond Theory concentrates on

individual bonds in a molecule and tends to ignore electrons not

used in bonding.

MOLECULAR ORBITAL MODELMOLECULAR ORBITAL MODEL

Molecular Orbital Theory assumes ALL

the orbitals of the atoms are able to take

part in bonding.

Every atom has a complete set of

orbitals, but not all of them contain

electrons

Remember that orbitals are really the solutions

of Schrodinger’s equation, and that they

are called wave-functions

r

1s wavefunction

2pz wavefunction

-

+

Negativehere

Positivehere

2pz orbital

- +

+

1s orbital

While wave functions can be

positive or negative, probabilities can only be positive.

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

they can cancel each other out.

..

..

..

+

+

+

+

+

plus

1sA 1sB

B

A

A

B

A sigma, , bonding orbital

..

..

.

+

+

+

-

+

minus

1sA 1sB

B

A

A

A sigma star, , anti-bonding orbital

-B.

The work on molecular orbitals can be generalized to

p-orbitals.

2pz2pz 2p

A 2p bonding orbital

2pz 2pz 2p

A 2p

antibonding orbital

plusA A BB

2p

y

2p

y

2p

A 2p bonding orbital

minusA AB B

2py2py

2p

A 2p

antibonding orbital

Many combinations of orbitals can produce

bonding and anti-bonding molecular orbitals, s with p,

d with p, etc.

Orbitals on the two Orbitals on the two bonding atoms must bonding atoms must

meet 2 conditionsmeet 2 conditions They must be similar in They must be similar in

energyenergy They must have the right They must have the right

symmetrysymmetry

2pz

2py

plus

2py

2pz

Orbitals pointing in different directions cannot overlap to

form molecular orbitals.

Molecular Orbital Molecular Orbital TheoryTheory

1. Molecular orbitals are 1. Molecular orbitals are made from atomic made from atomic orbitalsorbitals

2. Orbitals are conserved2. Orbitals are conserved3. Molecular orbitals form 3. Molecular orbitals form

in pairs: in pairs: bondingbonding & & antibondingantibonding

BondingBonding Molecular Orbital Molecular Orbital

Geometry favorable to Geometry favorable to overlapoverlap

When a bonding orbital is formed, the energy of the orbital is lower than

those of its parent atomic orbitals.

Anti-bonding Anti-bonding Molecular OrbitalMolecular Orbital

Geometry not Geometry not favorable to overlapfavorable to overlap

Similarly, when an anti-bonding orbital is

formed, the energy of the orbital is higher

than those of its parent atomic orbitals.

Bond Bond OrderOrder

# bonding e antibonding e

2

- - #

Molecular Orbital Diagrams

Examine someExamine somehomonuclear homonuclear

diatomicdiatomicmoleculesmolecules

HydrogenHydrogenHeliumHelium

1sA 1sB

2s

2s

ParamagneticParamagnetic

1. Responds to 1. Responds to magnetic fieldmagnetic field

2. Has unpaired 2. Has unpaired electronselectrons

DiamagneticDiamagnetic1. Does not respond to 1. Does not respond to magnetic fieldmagnetic field

2. All electron paired2. All electron paired

1s 1s

2s 2s

2px2px2py

2py2pz2pz

1s

1s

2s

2s

2p2p 2p

2p2p

2p

fluorine gas

1s 1s

2s 2s

2px2px2py

2py2pz2pz

1s

1s

2s

2s

2p2p 2p

2p2p

2p

oxygen gas

Using MO Theory, Using MO Theory, moleculesmolecules have an have an

electron configurationelectron configuration Oxygen gasOxygen gas ((1s1s))22((1s1s

**))2 2

((2s2s))22((2s2s**))2 2

((2py2py))2 2 ((2py2py**))22

((2pz2pz))2 2 ((2px2px))2 2

1s 1s

2s 2s

2px2px2py

2py2pz2pz

1s

1s

2s

2s

2p2p 2p

2p2p

2p

nitrogen gas Magnet Movie

Bond Strength

Bond Length

Strengths of Strengths of Localized Electron Localized Electron

ModelModel1. Simple1. Simple

2. Easy to understand2. Easy to understand

3. Predicts geometry of 3. Predicts geometry of molecule molecule

Limitations of Limitations of Localized Electron ModelLocalized Electron Model

1. Does not address 1. Does not address concept of resonance or concept of resonance or unpaired eunpaired e--

2. Cannot explain color in2. Cannot explain color in transition metal transition metal compounds compounds

Strengths of Strengths of Molecular Orbital ModelMolecular Orbital Model

1. Better represents 1. Better represents actual molecular systemactual molecular system

2. Provides basis for 2. Provides basis for explaining properties of explaining properties of molecular systemsmolecular systems

Limitations of Limitations of Molecular Orbital Molecular Orbital

ModelModel1. MO diagrams are complex.

2. MO diagrams are difficult for molecules with more than two atoms.

3. No prediction of geometry

Combining the Localized Electron

and Molecular Orbital

Models

Draw the Lewis structure of benzene

C6H6

Lewis Structure

C2H4 + Br2 C2H4Br2

C6H6 + Br2 NR

bonds in benzene

bonds in benzene

benzene

Isomerism Isomerism

Isomers – two or more compounds Isomers – two or more compounds with same molecular formula but with same molecular formula but different arrangements of atoms different arrangements of atoms

Cis – Trans Isomerism (NOT mirror Cis – Trans Isomerism (NOT mirror images of each other NOT super images of each other NOT super imposable.imposable.

CisCis Trans Trans

Resonance and MOResonance and MO

X X

The more resonance structures the more stable the molecule

Metals & SemiconductorsMetals & Semiconductors Read pg657-669Read pg657-669 Study Figures 1-23Study Figures 1-23

Know Know InsulatorsInsulators

Conductors, Semiconductors – intrinsic, Conductors, Semiconductors – intrinsic, extrinsicextrinsic

DopantsDopants