Lecture 12 - Molecular Orbital Theory

Flashcards covering key concepts from the lecture on Molecular Orbital Theory.

What does unpaired spins indicate about a substance's magnetic properties?

Unpaired spins indicate that the substance is attracted to a magnetic field, making it paramagnetic.

What are paired spins in the context of magnetic properties?

Paired spins are repulsed by a magnetic field, indicating that the substance is diamagnetic.

What happens to the electrons in Be2 compared to separate Be atoms?

The electrons in Be2 fill both bonding and antibonding orbitals and do not have lower energy than the electrons in 2 Be atoms, resulting in an unstable molecule.

How do p-orbitals behave when two atoms approach?

One pair of p-orbitals will have an end-on interaction, while two pairs of p-orbitals will have a side-on interaction.

What distinguishes sigma and pi orbitals?

Molecular orbitals are classified according to their symmetry; sigma orbitals resemble s-orbitals, while pi orbitals arise from side-on interactions of p orbitals.

What are degenerate orbitals?

Degenerate orbitals are those arising from side-on interactions of p orbitals that have the same energy.

In lighter elements like B₂, how does the energy of the σ 2p bonding orbital compare to the π 2p bonding orbitals?

In lighter elements, the σ 2p bonding orbital is actually higher in energy than the π 2p bonding orbitals.

What is the case for heavier elements like O₂ and F₂ regarding the σ and π 2p orbitals?

In heavier elements, the σ 2p bonding orbital is lower in energy than the π 2p bonding orbitals.

What are the characteristics of paramagnetic molecules?

Paramagnetic molecules have unpaired electrons and a net magnetic moment, making them drawn into magnetic fields.

How do diamagnetic molecules behave in magnetic fields?

Diamagnetic molecules do not have unpaired electrons and have no magnetic moment, resulting in weak repulsion by magnetic fields.

What is the significance of HOMO and LUMO in molecular orbital theory?

HOMO stands for Highest Occupied Molecular Orbital, while LUMO stands for Lowest Unoccupied Molecular Orbital; the lowest energy electronic transition is the HOMO-LUMO transition.