Q: Which of the following is a consequence of 'sp mixing' in the molecular orbital diagrams of second-period homonuclear diatomic molecules?

The energy ordering of the $$ ext{2}\\sigma_g$$ and $$ ext{1}\\pi_u$$ orbitals can change for lighter elements.

Question 1

Which of the following best describes the difference between a bonding and an antibonding molecular orbital (MO) formed from the overlap of two atomic orbitals (AOs)?

Accepted Answer

A bonding MO results from constructive (in-phase) overlap, while an antibonding MO results from destructive (out-of-phase) overlap.

Question 2

Consider the molecular orbital energy level diagram (MOELD) for O$$_2. $$Which property of O$$_2 is $$explained by the MO theory but not by the Lewis structure?

Accepted Answer

Paramagnetism due to the presence of unpaired electrons in the $$	ext{1}\pi_g^*$$ orbitals.

Question 3

Which of the following statements about the Linear Combination of Atomic Orbitals (LCAO) approach is correct?

Accepted Answer

The number of molecular orbitals formed equals the number of atomic orbitals combined.

Question 4

Given the following AO energies: H(1s) = $$-13.6 eV$$, Li(2s) = $$-5.4 eV$$, Li(1s) $$\ll -50 eV$$, what is the nature of the bond in LiH according to MO theory?

Accepted Answer

The bond is highly polar with the bonding MO localized more on hydrogen.

Question 5

Which of the following best explains why only certain atomic orbitals interact to form molecular orbitals in diatomic molecules?

Accepted Answer

Only atomic orbitals of the correct symmetry and similar energy can interact to form molecular orbitals.

Question 6

What is the bond order of F$$_2$$ according to the MOELD, given that the 2s and 2p AO energies are $$-40.0 eV $$and $$-18.1 eV$$, respectively?

Accepted Answer

1

Question 7

Which of the following is a consequence of 'sp mixing' in the molecular orbital diagrams of second-period homonuclear diatomic molecules?

Accepted Answer

The energy ordering of the $$	ext{2}\sigma_g$$ and $$	ext{1}\pi_u$$ orbitals can change for lighter elements.

Question 8

Which of the following best describes the effect of increasing the overlap between two atomic orbitals on the resulting bonding molecular orbital?

Accepted Answer

The bonding molecular orbital is more stabilized (lower in energy) relative to the atomic orbitals.

Question 9

In the context of molecular orbital theory, what is the significance of the terms 'gerade' (g) and 'ungerade' (u)?

Accepted Answer

'Gerade' means symmetric with respect to inversion through the center of the molecule, while 'ungerade' means antisymmetric.

Question 10

Which of the following best explains why the core 1s orbitals are typically not shown in the MOELD for second-period diatomic molecules?

Accepted Answer

They are much lower in energy and have minor contributions to overall bonding.

Question 11

A molecule has the following electron configuration in its molecular orbitals: $$(\sigma_{1s})^2$ (\sigma_{1s}^*)^2$ (\sigma_{2s})^2$ (\sigma_{2s}^*)^2$ (\pi_{2p})^4$ (\sigma_{2p})^2$. What is the bond order?

Accepted Answer

$$3$$

Question 12

Why does the molecular orbital model predict that O$$_2 is $$attracted into a magnetic field, while the Lewis structure does not?

Accepted Answer

MO theory shows O$$_2$$ has unpaired electrons, making it paramagnetic.

Question 13

Which of the following is a correct application of the bond order formula $$	ext{Bond order} = \frac{1}{2}[(\Sigma e^-_{	ext{Bonding}}) - (\Sigma e^-_{	ext{Antibonding}})]$$ for N$$_2$$?

Accepted Answer

Bond order = $$\frac{1}{2}[(10) - (4)] = 3$$

Question 14

Which of the following best explains why the bond in HF is highly polar according to MO theory?

Accepted Answer

The bonding MO is localized more on fluorine due to its much lower AO energy.

Question 15

Which of the following is NOT a general rule for the interaction of atomic orbitals to form molecular orbitals?

Accepted Answer

AOs that are far apart in energy interact strongly to form MOs.

Question 16

Which of the following best describes the effect of side-on overlap of two p orbitals in a homonuclear diatomic molecule?

Accepted Answer

It results in the formation of bonding and antibonding molecular orbitals of $$\pi$$ symmetry.

Question 17

Which of the following is a real-world application of molecular orbital theory as discussed in the lecture?

Accepted Answer

The aurora borealis, where ionized N$$_2$$ emits light upon returning to the ground state.

Question 18

Which of the following is true about the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)?

Accepted Answer

The HOMO is the highest energy MO containing electrons, and the LUMO is the lowest energy MO without electrons.

Molecular Orbital Theory and LCAO Models for Diatomic Molecules

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