Gen Chem 1 molecular orbital theory exam review

What is a molecular orbital?

A molecular orbital is a region in a molecule where electrons are likely to be found, formed from the combination of atomic orbitals.

True or False: Molecular orbitals can hold more than two electrons.

True. However, they must have opposite spins according to the Pauli Exclusion Principle.

Compare bonding and antibonding orbitals.

Bonding orbitals stabilize the molecule and lower energy; antibonding orbitals destabilize and have higher energy.

Fill in the blank: The principle that states electrons occupy the lowest energy orbitals first is called _____ principle.

Aufbau principle.

What is the significance of the energy gap between bonding and antibonding orbitals?

A larger energy gap indicates stronger bonds; smaller gaps can lead to instability and reactivity.

How do molecular orbitals form?

Molecular orbitals form by the constructive or destructive interference of atomic orbitals when atoms bond.

What is the shape of the bonding orbital in diatomic molecules?

Bonding orbitals typically have a symmetric shape around the bond axis, enhancing electron density between nuclei.

True or False: Each molecular orbital can hold a maximum of four electrons.

False. Each molecular orbital can hold a maximum of two electrons with opposite spins.

What does the MO theory predict about bond order?

Bond order is calculated as: Bond Order = (Number of bonding electrons - Number of antibonding electrons) / 2.

Cause → Effect: If all electrons are in bonding orbitals, then _____

The molecule is likely stable and has a higher bond order.

What happens to the energy levels of atomic orbitals when combining?

The energies of the atomic orbitals shift due to interaction, resulting in lower energy bonding and higher energy antibonding orbitals.

Explain the concept of degenerate orbitals.

Degenerate orbitals are orbitals that have the same energy level. For example, in a set of p orbitals.

How do hybrid orbitals relate to molecular orbitals?

Hybrid orbitals are formed from atomic orbitals mixing, which then can be used to form molecular orbitals.

Give an example of a diatomic molecule and its molecular orbitals.

O₂ has 10 electrons to fill MO: 5 in bonding, 1 in antibonding, resulting in a bond order of 2.

What is the role of symmetry in molecular orbital theory?

Symmetry determines the interaction and overlap of atomic orbitals, influencing the stability and properties of the molecule.

Fill in the blank: The hybridization state of a central atom is determined by the number of _____.

Electron domains.

What defines molecular orbitals?

Molecular orbitals (MOs) are formed by the linear combination of atomic orbitals (LCAO), where atomic orbitals combine to create bonding and antibonding orbitals.

True or False: MOs are identical to atomic orbitals.

False. MOs are distinct from atomic orbitals and result from their combination, leading to different energy levels and shapes.

Fill in the blank: Two atomic orbitals combine to form _____.

two molecular orbitals: one bonding and one antibonding.

Atomic orbital types include:

- s - p - d - f These orbitals differ in shape and energy.

How do atomic orbitals combine?

They combine through constructive (bonding) or destructive (antibonding) interference, influencing the stability of the resulting molecular orbital.

What happens to energy levels in bonding orbitals?

Bonding orbitals are lower in energy than the original atomic orbitals, promoting stability in the molecule.

Cause → Effect: Atomic orbital overlap leads to _____

the formation of molecular orbitals, influencing molecular bonding and stability.

Compare bonding and antibonding molecular orbitals.

Bonding orbitals increase stability; antibonding orbitals decrease stability and are higher in energy.

What is the outcome of destructive interference?

Destructive interference of overlapping atomic orbitals creates antibonding orbitals, which have nodes and higher energy.

Short example of LCAO: 1s orbitals of H atoms.

Two 1s atomic orbitals from H combine to form: - One bonding MO (σ) - One antibonding MO (σ*)

Energy order for simple diatomic molecules:

For homonuclear diatomics (e.g., N₂): σ(1s) < σ*(1s) < σ(2s) < σ*(2s) < σ(2p) < π(2p) < π*(2p) < σ*(2p)

What is the significance of molecular orbital theory?

It explains molecular structure, electronic configurations, and magnetic properties of molecules, beyond simple valence bond theory.

What is a molecular orbital diagram?

A graphical representation of molecular orbitals in a molecule, showing energy levels and electron occupancy.

True or False: Antibonding orbitals are lower in energy than bonding orbitals.

False. Antibonding orbitals are higher in energy than bonding orbitals.

How are molecular orbitals formed?

Molecular orbitals are formed by the linear combination of atomic orbitals (LCAO).

Fill in the blank: In a molecular orbital diagram, the number of molecular orbitals equals the number of ___.

atomic orbitals combined.

Compare bonding and antibonding orbitals.

Bonding orbitals: lower energy, stabilize molecule. Antibonding orbitals: higher energy, destabilize molecule.

Describe the Aufbau principle in molecular orbital filling.

Electrons fill the lowest energy molecular orbitals first before moving to higher energy levels.

What is the order of filling MOs for diatomic molecules?

For O2, F2: σ(2s), σ*(2s), σ(2p), π(2p), π*(2p), σ*(2p).

Cause → Effect: Electrons in bonding orbitals result in ___

Attraction between nuclei and stabilization of the molecule.

Which orbitals are occupied first in O2?

σ(2s), σ*(2s), σ(2p), π(2p) (then π*(2p) and σ*(2p) if needed).

How to determine bond order?

Bond order = (number of electrons in bonding MOs - number in antibonding MOs) / 2.

True or False: A higher bond order indicates a weaker bond.

False. A higher bond order indicates a stronger bond.

Example: For N2, calculate bond order.

N2 has 10 electrons in bonding MOs and 2 in antibonding. Bond order = (10 - 2) / 2 = 4.

Bonding orbitals vs. Antibonding orbitals?

Bonding orbitals stabilize a molecule, while antibonding orbitals destabilize it.

True or False: Antibonding orbitals have higher energy than bonding orbitals.

True. Antibonding orbitals result from destructive interference of wave functions, yielding higher energy.

Define hybridization.

Hybridization is the mixing of atomic orbitals to form new hybrid orbitals for bonding.

What does sp3 hybridization indicate?

sp3 hybridization involves one s and three p orbitals, forming four equivalent hybrid orbitals.

Fill in the blank: Bonding orbitals are ________ in energy than the original atomic orbitals.

lower

Cause of hybridization?

Mixing orbitals allows for better overlap and stronger bonds in molecules.

Example of sp2 hybridized molecule?

Ethylene (C2H4) has sp2 hybridization, allowing for a double bond.

What happens in antibonding orbital formation?

Two atomic orbitals combine destructively, resulting in a node between the nuclei.

List types of hybridization.

- sp - sp2 - sp3 - dsp3 - d2sp3

True or False: Hybrid orbitals are directed towards electron pairs.

True. Hybrid orbitals arrange themselves to minimize electron pair repulsion.

Bond order formula?

Bond order = \\frac{(number\ of\ bonding\ electrons - number\ of\ antibonding\ electrons)}{2}

What is the bond order of O2?

O2 has a bond order of 2, indicating a double bond.