Question 1

According to molecular orbital (MO) theory, which of the following best describes a chemical bond?

Accepted Answer

A chemical bond is formed when atomic orbitals combine to produce molecular orbitals that are occupied by electrons delocalized over the entire molecule.

Question 2

Which of the following molecules is predicted to be paramagnetic according to molecular orbital theory?

Accepted Answer

$$\mathrm{O_2$}$$

Question 3

Which statement best explains the difference between bonding and antibonding molecular orbitals?

Accepted Answer

Bonding orbitals result from constructive interference of atomic orbitals and have lower energy, while antibonding orbitals result from destructive interference and have higher energy.

Question 4

Which of the following best describes resonance in the context of molecular orbital theory?

Accepted Answer

Resonance is the delocalization of electrons across multiple atoms, as described by electrons occupying molecular orbitals that extend over several nuclei.

Question 5

Given the following molecular orbital electron configuration for a diatomic molecule: $$\sigma_{2s}^2\,\sigma_{2s}^*{}^2\,\pi_{2p_x}^2\,\pi_{2p_y}^2\,\sigma_{2p_z}^2$$, what is the bond order?

Accepted Answer

3

Question 6

Which of the following molecules or ions has a bond order of zero according to molecular orbital theory?

Accepted Answer

$$\mathrm{He_2$}$$

Question 7

Why is $$\mathrm{O_2$}$$ paramagnetic according to molecular orbital theory?

Accepted Answer

Because it has two unpaired electrons in its $$\pi^*$$ antibonding molecular orbitals.

Question 8

Which of the following best describes a nonbonding molecular orbital?

Accepted Answer

A molecular orbital that does not contribute to bond order because it is neither bonding nor antibonding.

Question 9

Which of the following is a correct electron configuration for the molecular orbitals of $$\mathrm{C_2$}$$?

Accepted Answer

$$\sigma_{2s}^2\,\sigma_{2s}^*{}^2\,\pi_{2p_x}^2\,\pi_{2p_y}^2$$

Question 10

Which of the following statements about the difference between molecular orbital theory and valence bond theory is correct?

Accepted Answer

Molecular orbital theory describes electrons as delocalized over the entire molecule, while valence bond theory describes electrons as localized between atoms.

Question 11

A student is asked to determine if $$\mathrm{B_2$} is $$paramagnetic or diamagnetic using molecular orbital theory. Which of the following is the correct reasoning?

Accepted Answer

$$\mathrm{B_2$} is $$paramagnetic because it has two unpaired electrons in the $$\pi_{2p}$$ orbitals.

Question 12

Which of the following best explains why $$\mathrm{He_2$}$$ does not exist under normal conditions?

Accepted Answer

Because the bond order is zero, indicating no net bonding interaction.

Question 13

Which of the following is the correct order of increasing energy for the molecular orbitals formed from $$2p$$ atomic orbitals in $$\mathrm{O_2$}$$?

Accepted Answer

$$\sigma_{2p_z} \u003c \pi_{2p_x} = \pi_{2p_y} \u003c \pi_{2p_x}^* = \pi_{2p_y}^* \u003c \sigma_{2p_z}^*$$

Question 14

A patient is exposed to high concentrations of $$\mathrm{CO} ($$carbon monoxide). Using molecular orbital theory, explain why $$\mathrm{CO}$$ binds strongly to hemoglobin.

Accepted Answer

Because the highest occupied molecular orbital (HOMO) of $$\mathrm{CO}$$ can donate electron density to the iron atom in hemoglobin, forming a strong coordinate bond.

Question 15

Which of the following best describes the effect of increasing the number of electrons in antibonding molecular orbitals?

Accepted Answer

It decreases the bond order and weakens the bond.

Question 16

Which of the following is a correct statement about the shapes of molecular orbitals compared to the shapes of atomic orbitals?

Accepted Answer

Molecular orbitals can have different shapes and symmetries compared to atomic orbitals, depending on the combination and phase of the atomic orbitals.

Question 17

Which of the following best explains why $$\mathrm{N_2$}$$ has a higher bond order than $$\mathrm{O_2$}$$?

Accepted Answer

$$\mathrm{N_2$}$$ has fewer electrons in antibonding orbitals than $$\mathrm{O_2$}.$$

Question 18

Which of the following is the correct formula for calculating bond order using molecular orbital theory?

Accepted Answer

$$	ext{Bond order} = \frac{	ext{number of electrons in bonding MOs} - 	ext{number of electrons in antibonding MOs}}{2}$$

Molecular Orbital Theory and Chemical Bonding: Study Guide

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