chemical bonding 4 hybrid...valence bond theory and lone pairs (e.g. h 2 o) building h 2 o with...

Chemical Bonding 4.8

Valence Bond TheoryHybrid Orbital Theory

Multiple Bonds

© 2009 High School Chem Solutions. All rights reserved.

Valence Bond Theory

•

Combines Lewis’

theory of filling octets by sharing pairs of electrons with the electron configuration of atomic orbitals.

•

Valence Bond Theory states that bonding occurs when atomic orbital overlap.


Building BF3

with Valence Bond Theory

B:1s 2s 2p

F:1s 2s 2p


Building BF3

with Valence Bond Theory

B:1s 2s 2p

Boron enters an excited state where an electron from the 2s orbital is promoted to the 2py

orbital.


Valence Bond Theory has problems with the shape

2s2px

2py

F

F

FB

Valence Bond Theory Views bonding as an overlapping of atomic orbitals.

Gets the bond angle wrong


Problems with Valence Bond Theory and BF3

Problem (the bond angle is wrong)•

Valence Bond Theory says 90o

and a random

angle for the fluorine bonded to the s-orbital.•

VSEPR theory says 120o

Solution (Hybrid Orbitals)•

When the electron is promoted, the 2s, 2px

, and 2py

orbitals

of boron morph into three separate sp2 hybrid orbitals

that are identical

in shape and size. © 2009 High School Chem Solutions. All rights reserved.

sp2

Hybrid Orbitals

The 2s and two 2p orbitals

morph into three identical sp2

hybrid orbitals

F

F

F

sp2

sp2

sp2


sp2

Hybrid Orbitals

+ + =s

p

p

sp2

sp2

sp2


sp3

Hybrid Orbitals

(e.g. CH4

)

H:1s

C:1s 2s 2p


sp3

Hybrid Orbitals

(e.g. CH4

)

H:1s

C:1s 2s 2p

Hybridization of Carbon C:

1s sp3


sp3

Hybrid Orbitals

(e.g. CH4

)

sp3

sp3

sp3 sp3

HH H

Bond Angle = 109.5o

H


Valence Bond Theory and Lone Pairs (e.g. H2

O)

Building H2

O with Valence Bond TheoryH: H:

1s 1sO:

1s 2s 2p Oxygen could accept one electron from one

Hydrogen in its py

orbital and another from the other Hydrogen in its pz

orbital.© 2009 High School Chem Solutions. All rights reserved.

•

Valence Bond Theory views bonding as an overlapping of atomic orbitals.

pxpz

pyH

H

py

pxpz

Valence Bond Theory get the angle wrong again!

Valence Bond Theory and Lone Pairs (e.g. H2

O)


Problems with Valence Bond Theory in the H2

O Example

•

The bond angle is wrong.•

Valence Bond Theory predicts 90o

•

VSEPR Theory predicts 104.5o

•

The orbital shape must be wrong.•

Shared electrons are not spending enough time with the Hydrogen.


Hybrid Orbital Theory and Lone Pairs (e.g. H2

O)

H: H:1s 1s

O:1s sp3

Electrons are not promoted here, but every orbital in the

n = 2 energy level becomes

hybridized. © 2009 High School Chem Solutions. All rights reserved.

sp3

Hybrid Orbitals

(H2

O)

sp3

sp3sp3

sp3

H

H

Bond Angle = 104.5o

Four sp3

hybrid orbitals are formed


Hybrid Orbital Theory and 5 Charge Clouds! (e.g. PCl5

)

:Cl:

P Cl:

:Cl:

..

..

:Cl:....

:Cl..

..

..


sp3d Hybrid Orbitals

P: 3s 3p 3d

PromotionP:

3s 3p 3dHybridization

P:sp3d

Atomic Orbitals


Hybrid Orbital Theory and 6 Charge Clouds! (e.g. SF6

)

:F:

S

:F:

....

:F:....

:F..

..:F:

F:....


sp3d2

Hybrid Orbitals

S: 3s 3p 3d

PromotionS:

3s 3p 3dHybridization

S:sp3d2

Atomic Orbitals


Summary

Charge Clouds Hybridization2 sp3 sp2

4 sp3

5 sp3d6 sp3d2


Double Bonds (e.g. C2

H4

)

H HC C

H HEach carbon has 3 charge clouds.

sp2

hybrid orbitals


Double Bonds (e.g. C2

H4

)

C: 2s 2p

PromotionC:

2s 2pHybridization

C:sp2 2p

Atomic Orbitals


sp2

sp2

sp2sp2

sp2

sp2

p

p

H

H

H

H

π

Bond

σ

Bond

Double Bond (C2

H4

)


Triple Bonds (e.g. C2

H2

)

H C C H

Each carbon has two charge clouds.

sp hybrid orbitals


Triple Bonds (e.g. C2

H2

)

C: 2s 2p

PromotionC:

2s 2pHybridization

C:sp

2p

Atomic Orbitals


Triple Bond (C2

H2

)

σ

Bond

Two π

Bonds

sp spspsp

p p

pp


chemical bonding 4 hybrid...valence bond theory and lone pairs (e.g. h 2 o) building h 2 o with...

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