8. MO energy level diagrams Flashcards
What are the rules that must be followed in order to combine AO into MO?
Explain the bonding and antibonding orbital formation + draw the MO energy diagram
AOs overlap in phase - bonding decreases the E of the MO → more stable (ground state) → bond shares a pair of e
AOs overlap out of phase - antibonding increases the E of the MO → less stable
Drawing must have:
- axis
- orbitals with atoms
- molecular orbitals
- symmetry labels
- parity labels
- show how orbitals overlap (VB addition)
Rank molecules in order of stability H2, H2+ and H2-?
- H2 most stable because highest bond order (B.O. = 1)
- Both H2+ and H2- are of same bond order (B.O. = 0.5) BUT their e in MO diagram occupy different E MOs → H2- has e in antibonding MO → less stable than H2+ which has one 1 only in bonding (lowe E)
How do the bonds change when atoms get larger?
The bonds become weaker because their nuclei are further apart → attracted weaker → overlap is worse (Li in Li2 overlap further than H in H2)
How do bonding and antibonding p orbitals look (picture) when overlap by the ends for a MO?
Sigma symmetry - same phase when rotated by 180 degrees
How do bonding and antibonding p orbitals look (picture) when overlap sideways for a MO?
Pi symmetry because the phase changes when rotated by 180 degrees (bonding orbital - in phase) - overlap sideways
Sigma symmetry of antibonding (out of phase) orbotal - no phase chnage when rotated 180 degrees - overlap by the ends
What are the possible non-bonding interactions?
No change - no orbital combination
In phase and out of phase cancel each other out
How does F2 MO energy diagram look with pictures of in phase / out of phase orbital overlap?
Explain LUMOs vs HOMOs
When speaking of reactivity
What is the MO energy diagram for oxygen?
What is the order for constructing MO energy diagrams?
