Molecular Orbital Theory and Properties

Flashcards covering key concepts related to Molecular Orbital (MO) Theory and its implications for molecular structure and properties.

What does Molecular Orbital (MO) Theory explain in a molecule?

MO theory explains bonding in a molecule and molecular properties.

What are the two types of molecular orbitals mentioned in MO Theory?

Bonding MOs (σ, π) and Anti-bonding MOs (σ, π).

What causes a molecule like oxygen (O2) to be paramagnetic?

O2 has unpaired electrons in its molecular orbitals.

What happens to electrons in a bond when they occupy bonding molecular orbitals?

Electrons in bonding MOs stabilize the molecule.

What is the significance of the bond order?

Bond order indicates the stability and strength of a bond; calculated as (Number of bonding electrons - Number of antibonding electrons) / 2.

What is the shape of bonding and antibonding molecular orbitals?

Bonding MOs have higher electron density between the nuclei, while antibonding MOs have a node where electron density is zero.

What principle states that electrons fill the lowest energy orbitals first?

Aufbau principle.

In the molecular orbital diagram of H2, what is the bond order?

Bond order is 1.0, indicating a single bond.

What is the expected stability of a molecule with equal numbers of bonding and antibonding electrons?

Such a molecule is unstable, as seen in He2 with a bond order of 0.

When two waves are in phase, what kind of interference do they exhibit?

Constructive interference.

What is the bond order for an H2+ molecule?

Bond order is 0.5.

Does He2 molecule exist based on MO theory?

No, He2 does not exist because it has a bond order of 0.

When electrons are placed in antibonding MOs, what is the effect on the molecule?

It destabilizes the molecule due to higher energy levels.

How does MO theory help explain why some molecules exist?

MO theory shows that molecules with more bonding electrons than antibonding electrons are stable.

What is the effect of electron pairing in molecular orbitals?

Electrons with opposite spins can occupy the same molecular orbital, following Pauli's exclusion principle.

What does the term 'diamagnetic' mean in the context of molecular orbitals?

A diamagnetic molecule has all electrons paired and is not attracted to a magnetic field.

When two waves are out of phase, what kind of interference do they exhibit?

Destructive interference, which leads to electron density being zero in antibonding orbitals.

What is the key difference in energy levels between bonding and antibonding molecular orbitals?

Bonding MOs are lower in energy than the atomic orbitals from which they are formed, while antibonding MOs are higher in energy.

What principle states that electrons will individually occupy degenerate orbitals before pairing up?

Hund's rule.

When valence atomic orbitals combine, how many molecular orbitals are formed?

The number of molecular orbitals formed is equal to the number of atomic orbitals that combine.

What does 'paramagnetic' mean in the context of molecular orbitals?

A paramagnetic molecule has one or more unpaired electrons and is attracted to a magnetic field.

How are sigma (σ) molecular orbitals generally formed?

Sigma (σ) MOs are typically formed by the head-on overlap of atomic orbitals (e.g., s-s, s-p, pz-pz).

How are pi (π) molecular orbitals generally formed?

Pi (π) MOs are formed by the sideways overlap of parallel atomic orbitals (e.g., px-px, py-py).

How do bonding (σ and π) and antibonding (σ* and π*) molecular orbitals visually differ?

Bonding MOs exhibit constructive interference, concentrating electron density between atomic nuclei. Antibonding MOs show destructive interference, forming a nodal plane with zero electron density between nuclei.

What is a nodal plane in a molecular orbital, and what does it signify?

A nodal plane is a region within a molecular orbital where the probability of finding an electron is zero, typically formed in antibonding orbitals due to destructive interference.