Energy level diagrams
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What do energy level diagrams show?
Which molecular orbitals have a lower or higher energy
How are the orbitals filled up?
Bonding orbitals are filled first as they have the lowest energy
How do you calculate bond order?
1/2 (Number of bonding electrons - number of antibonding electrons)
How do you draw the backbone structure for an energy level diagram?
Arrow up the side labelled energy Bonding MO at. the bottom Antibonding MO at the top Atomic orbitals drawn in the middle
When is a significant orbital overlap achieved?
When atomic orbitals have similar energies, appropriate relative shapes, Orientations that provide some overlap
What is the relative shape of orbitals with a positive overlap integral which looks like an s orbital?
• No nodes containing both nuclei - They look like circles
Which atomic orbitals are combined to give the shape of an s orbital with a positive overlap integral?
s and s s and Px Px and Px
What is the relative shape of orbitals with a positive overlap integral which looks like a p orbital?
• They have one node containing both nuclei - The overlapping part of the orbitals resemble an atomic p orbital
Which atomic orbitals are combined to give the shape of a p orbital with a positive overlap integral?
Py and Py Py and d
What is the relative shape of atomic orbitals which form a zero overlap integral?
Non bonding One orbital has a node of the z axis and the other doesn’t The shape of the two atomic orbitals are not similar
When a molecular orbital looks like a s atomic orbital, what is it called?
σ molecular orbital
When a moelcular orbital looks like a p atomic orbital, what is it called?
π molecular orbital
What symmetry does π indicate?
Nodal plane between the two lobes
What symmetry does σ indicate?
Symmetry with respect to the rotation of the bond axis (z)
Why is Pz and Pz more stable?
Lower in energy, when they have sigma bonds
What type of bond does Px and Py form?
π bond
What are π and σ molecular orbitals not?
Degenerate
What is formed when two Pz orbitals overlap end on?
both σ (bonding) and σ* (antibonding) molecular orbitals
What is formed when two Py orbitals overlap sideways?
both π (bonding) and π* (antibonding) molecular orbitals
What is formed when Px orbitals overlap sideways?
both π (bonding) and π* (antibonding) molecular orbitals on a perpendicular plane to that of the orbitals formed by Py