Diatomic Molecules Flashcards
Atomic orbitals must be … to give Molecular orbitals
Same Symmetry
What 3 factors increases the strength of the interaction between atomic orbitals
- AOs that are closer in energy interact more strongly
- AOs that are close in energy to the MO contribute more than those that are further away
- AOs with compatible sizes interact more strongly
The number of MOs is equal to
The number of interacting AOs
As the energy seperation increases…
The lower energy atomic orbital contributes more to the bonding Molecular orbital, while the high energy atomic orbital contributes ,ore to the antibonding molecular orbtial
Why does no interaction occur between atomic orbitals when the energy seperation is very large
When the energy seperating is very large, the bonding MO is essentially the same as the lower energy AO, and the antibonding MO is essentially the same as the higher energy AO
In other words there is no longer any interaction
What type of symmetry do 2s orbitals have
2s orbitals have the same spherical symmetry as 1s orbitals and overlap in the same way to form MOs with cylindrical (sigma) symmetry
The bonding MO has σg symmetry and the antibonding MO has σu symmetry
How does the overlap between the 2pz atomic orbitals occur
The 2pz orbitals (point along the internuclear axis) overlap in a head-to-head fashion to form a bonding σg MO (with electron density between the atomic nuclei) and a head-to-head to form an anti-bonding σu MO
How does the overlap between the 2px and 2py atomic orbitals occur
The 2px and 2py orbitals (point perpendicular to the internuclear axis) overlap sideways on to give bonding an antibonding MOs
The resulting Mos do not have cylindrical symmetry, but have one nodal plane which contains the internuclear axis.
It has the symmetry lable π, where the bonding orbital has πu and the antibonding has πg inversion symmetry
Overlap between the 2s and 2p AOs can be negleted for
Elements on the right of the second period
When constructing a MO diagram, an element has unpaired electrons, this means it is
Paramagnetic
Attracted to a magnet
When constructing a MO diagram, an element has paired electrons, this means it is…
Diamagnetic
Repelled by a magnetic
How is bond order calculated
1/2 (Bonding electrons - Antibonding electrons)
The energy separation between the 2s and 2p AOs decreases towards the left of the second period
This causes
s-p-mixing
Results in a decrease in energy for the 2σ MOs and an increase in energy for the 3σ MOs
An example of large s-p-mixing is shown in the diagram
What wavelength are required for electronic transition
UV or visible eletromagnetic radiaition
How could you measure electronic transition from the HOMO to LUMO
The lowest energy (longest wavelength) transition in any molecule involves promoting an electron from the HOMO to the LUMO
However not very accurate due to electrostatic repulsion
