MO Diagrams for Diatomic Molecules
MO Diagrams for Diatomic Molecules
Chapter 5
Friday, October 9, 2015
Homonuclear Diatomic Molecules
What happens when we move to more complicated systems? Consider O2.
? The Lewis dot structure famously predicts the wrong electronic structure for O2
? We can use LCAO-MO theory to get a better picture:
Notice that
E > E, because the 2pa
E E
2pb
bonds have
more overlap
than bonds
2sa
2sb
Electron Configurations and Bond Orders
Just as with atoms, we can write a molecular electron configuration for O2
2*224*2
We can also calculate the O?O bond order:
BO
1 2
#
bonding
e
#
anti-bonding
e
1 8 4 2
2
LCAO MO theory also predicts (correctly) that O2 has two unpaired electrons.
Orbital Mixing
Orbitals of similar but unequal energies can interact if they have the same symmetry The 2s and 2pz orbitals form MOs with the same symmetry (g and u). sp mixing causes the g and u MOs to be pushed apart in energy:
The and orbitals change order!
The size of the effect depends on the 2s-2p energy difference.
Orbital Mixing
order changes
small Zeff = small energy
difference =
large sp mixing
large Zeff = large energy
difference =
small sp mixing
MOs of Homonuclear Diatomic Molecules
The MO picture of homonuclear diatomic molecules depends on the amount of sp mixing.
Li2, Be2, B2, C2, N2
O2, F2, Ne2
Bond Order and Bond Distance
The MO bond order is the main factor controlling the internucelar distance.
B2 2*22 BO = 1
C2 2*24 BO = 2
C22? 2*242
BO = 3
F2 2*224*4
BO = 1
O2? 2*224*3
BO = 1.5
O2 2*224*2
BO = 2
N2+ 2*241 BO = 2.5
O2+
2*224*1
N2 2*242
BO = 2.5
BO = 3
Relative AO Energies for MO Diagrams
Photoelectron spectroscopy gives us a pretty good idea of the relative energies for AOs.
Al
Li
H
Be
?13.6 eV
1s
B B
C N
Na Mg
Al
Si
P
S
3p
Cl Ar
O
2p
F ?18.6 eV
3s Si
C 2s
Ne
P
He
S
N
Cl
Ar
O
F ?40.2 eV Ne
................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related download
- 1 make your own comic
- mo diagrams for diatomic molecules
- design construction and operation of a small homemade
- wind turbine design nrel
- ac electrical generators brown university
- design of an energy efficient bicycle
- improved alpha tested magnification for vector textures and
- portable oxygen generating device design
- small scale vertical axis wind turbine design
- differentiable generator nets
Related searches
- free wiring diagrams for cars
- electrical wiring diagrams for cars
- wiring diagrams for free
- diagrams for photosynthesis in order
- grams to molecules formula
- molecules to grams equation
- semi trailer diagrams for training
- mo road sign test for license renewal
- free diagrams wiring for cars
- weather forecast for kansas city mo area
- rating for mo secretary of state
- phasor diagrams for ac circuits