Post on 14-Apr-2018
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Polyatomic species: contains three or more atoms
Three approaches to bonding in diatomicmolecules
1.Lewis structures
2.Valence bond theory
3.Molecular orbital theory
Chapter 5
Bonding in polyatomic molecules
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Orbital hybridization - sp
Hybrid orbitals generated by mixingthe characters of atomic orbitals
)(2
122_ xpshybridsp
+=
)(2
122_ xpshybridsp
=
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Orbital hybridization sp2
xpshybridsp 22_2
3
2
3
1 +=
yx ppshybridsp 222_22
1
6
1
3
1 +=
yx ppshybridsp 222_2
2
1
6
1
3
1 =
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sp3 hybrid orbitals one s and threep atomic orbitals mix toform a set of four orbitals with different directional properties
( )zyx pppshybridsp 2222_3 2
1 +++=
( )zyxpppshybridsp
2222_3 2
1 +=
( )zyx pppshybridsp 2222_3 2
1 +=
( )zyxpppshybridsp
2222_3 2
1 =
sp3d hybrid orbitals one s, threep, and one datomic orbitalsmix to form a set of five orbitals with different directional properties
[Ni(CN)5]3-
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Valence bond theory multiple bonding in polyatomic molecules
Valence bond theory multiple bonding in polyatomic molecules
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Valence bond theory multiple bonding in polyatomic molecules
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Molecular orbital theory:
l ig a n d g r o u p o r b i t a l approach in triatomic molecules
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Molecular orbital theory: BF3
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S3
S3
1
2
3
S3
3
1
2
S3
2
3
1
1
2
3
S3
3
1
2
2
3
1
Consider the S3 operation (=C3h) on the pz orbitals in the F3 fragment.
S3
C32
hC3
Unique, S3
Unique, S32
The resulting wavefunction contributions from the S3 and S32
operations are 3 and 2, respectively.
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BF3 Resonance StructuresBF3 Resonance Structures
The presence of the
resonance
contributions account
for the partial double
bond character in BF3
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SF6
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3
1
2
4
6
5 Find number of unchanged radial 2p
orbitals that are unchanged under each Ohsymmetry operation.
C2 Note the C2 axis bisect the planescontaining 4 p orbitals. The C2 axiscontains no 2p orbitals.
0
S6
0
S4
24022006
dhiC2(C4
2)
C4C2C3E
C2
Use the reduction formula to find the resulting symmetries: a1g, t1u, eg
Could derive the equations for the LGOs for the F6 fragment.
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( )65432116
1)( +++++=ga
( )6111
2
1)( =ut
( )4221
2
1)( =ut
( )5331
2
1)( =ut
( )6543211 22
12
1)( +=ge
( )54322
2
1)( +=ge
Three-center two-electron interactions
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