Chemical Bonding 4 Hybrid...Valence Bond Theory and Lone Pairs (e.g. H 2 O) Building H 2 O with...
Transcript of 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
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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.
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Building BF3
with Valence Bond Theory
B:1s 2s 2p
F:1s 2s 2p
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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.
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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
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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
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sp2
Hybrid Orbitals
+ + =s
p
p
sp2
sp2
sp2
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sp3
Hybrid Orbitals
(e.g. CH4
)
H:1s
C:1s 2s 2p
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sp3
Hybrid Orbitals
(e.g. CH4
)
H:1s
C:1s 2s 2p
Hybridization of Carbon C:
1s sp3
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sp3
Hybrid Orbitals
(e.g. CH4
)
sp3
sp3
sp3 sp3
HH H
Bond Angle = 109.5o
H
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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)
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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.
© 2009 High School Chem Solutions. All rights reserved.
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
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Hybrid Orbital Theory and 5 Charge Clouds! (e.g. PCl5
)
:Cl:
P Cl:
:Cl:
..
..
:Cl:....
:Cl..
..
..
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sp3d Hybrid Orbitals
P: 3s 3p 3d
PromotionP:
3s 3p 3dHybridization
P:sp3d
Atomic Orbitals
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Hybrid Orbital Theory and 6 Charge Clouds! (e.g. SF6
)
:F:
S
:F:
....
:F:....
:F..
..:F:
F:....
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sp3d2
Hybrid Orbitals
S: 3s 3p 3d
PromotionS:
3s 3p 3dHybridization
S:sp3d2
Atomic Orbitals
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Summary
Charge Clouds Hybridization2 sp3 sp2
4 sp3
5 sp3d6 sp3d2
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Double Bonds (e.g. C2
H4
)
H HC C
H HEach carbon has 3 charge clouds.
sp2
hybrid orbitals
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Double Bonds (e.g. C2
H4
)
C: 2s 2p
PromotionC:
2s 2pHybridization
C:sp2 2p
Atomic Orbitals
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sp2
sp2
sp2sp2
sp2
sp2
p
p
H
H
H
H
π
Bond
σ
Bond
Double Bond (C2
H4
)
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Triple Bonds (e.g. C2
H2
)
H C C H
Each carbon has two charge clouds.
sp hybrid orbitals
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Triple Bonds (e.g. C2
H2
)
C: 2s 2p
PromotionC:
2s 2pHybridization
C:sp
2p
Atomic Orbitals
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Triple Bond (C2
H2
)
σ
Bond
Two π
Bonds
sp spspsp
p p
pp
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