Molecular Orbitals and Quantum Ideas
From Atomic Orbitals to Molecular Orbitals
A More Complete Bonding Picture
Molecular orbital theory treats electrons as occupying orbitals that extend over an entire molecule. Bonding orbitals lower energy, antibonding orbitals raise it, and the bond order is , where and are bonding and antibonding electrons.
What is the bond order of in molecular orbital theory?
Two electrons fill the bonding orbital and none fill antibonding orbitals, so bond order is .
Correct answer: 1
What does a higher bond order generally imply?
Higher bond order usually correlates with greater bond strength and shorter bond length.
Correct answer: a stronger and shorter bond
HOMO-LUMO and Reactivity
Frontier Orbitals
The highest occupied molecular orbital, or HOMO, and the lowest unoccupied molecular orbital, or LUMO, help explain reactivity, electron donation, and electron acceptance. Small HOMO-LUMO gaps often correspond to easier electronic excitation and higher chemical reactivity in certain systems.
Which orbital is typically associated with electron donation?
The HOMO is the highest occupied orbital and is often the electron-donating orbital.
Correct answer: HOMO
What does HOMO stand for?
HOMO is the standard acronym in molecular orbital theory.
Correct answer: highest occupied molecular orbital
Conceptual Bridge
Lewis structures are useful for intuition, but molecular orbital theory explains delocalization, magnetism, and many subtle bonding effects more completely.