Question 1

A Lewis acid is a substance that can accept an electron pair. Which orbital will the new electron occupy if $$\mathrm{$$SiH_3$$^+}$$ accepts an electron pair?

Accepted Answer

Unoccupied $$sp^2$$ hybrid orbital

Question 2

When electrons in a molecule are excited by absorption of photons, which molecular orbitals do they occupy in the excited state?

Accepted Answer

Electrons move from the $$\pi$$ orbital to the $$\pi^*$$ orbital

Question 3

In the molecular orbital diagram for the C–F bond of fluoromethane, if two more electrons are added to the bond, where would these electrons go?

Accepted Answer

These electrons would go to the $$\sigma^*$$ orbital

Question 4

Which kind of molecular orbitals are formed when two atomic p orbitals combine side-by-side?

Accepted Answer

$$\pi$$ bonding molecular orbital

Question 5

For trans-hex-3-ene, will there be free rotation around the C3–C4 bond? Explain.

Accepted Answer

There will be no free rotation around the C3–C4 bond due to the presence of a pi bond

Question 6

Which of the following best describes a Lewis acid?

Accepted Answer

A substance that accepts an electron pair

Question 7

Which molecular orbital is higher in energy: $$\sigma or$$ $$\sigma^*$$?

Accepted Answer

$$\sigma^*$$ orbital

Question 8

If two atomic orbitals combine end-to-end, what type of molecular orbital is formed?

Accepted Answer

$$\sigma$$ bonding molecular orbital

Question 9

Which of the following statements about the $$\pi$$ bond in ethene ($$\mathrm{C_2H_4}) is $$correct?

Accepted Answer

The $$\pi$$ bond restricts rotation around the C=C bond

Question 10

Which of the following is true about the electron configuration in the ground state of a molecule?

Accepted Answer

Electrons occupy the lowest available energy orbitals

Question 11

What is the effect of adding electrons to an anti-bonding molecular orbital?

Accepted Answer

It decreases the bond order

Question 12

Which of the following best explains why there is no free rotation around a double bond?

Accepted Answer

The $$\pi$$ bond prevents rotation due to its electron density above and below the plane of the atoms

Question 13

Which orbital is typically unoccupied in a trigonal planar Lewis acid such as $$\mathrm{BF_3$}$$?

Accepted Answer

$$sp^2$$ hybrid orbital

Question 14

If a molecule absorbs a photon and an electron is promoted from a bonding $$\pi$$ orbital to an anti-bonding $$\pi^*$$ orbital, what happens to the bond order?

Accepted Answer

Bond order decreases

Question 15

Which of the following is a correct statement about molecular orbitals?

Accepted Answer

Anti-bonding molecular orbitals are higher in energy than bonding molecular orbitals

Question 16

Which of the following is true about the $$\sigma$$ bond in ethane ($$\mathrm{C_2H_6}$$)?

Accepted Answer

There is free rotation around the C–C bond

Question 17

Which of the following best describes the effect of extremely low temperatures on electron excitation?

Accepted Answer

Electrons remain in the lowest energy orbitals

Question 18

Which of the following is a consequence of electron promotion from a bonding to an anti-bonding orbital in a molecule?

Accepted Answer

The molecule becomes less stable

Question 19

Which of the following is true about the molecular orbital diagram for $$\mathrm{O_2$}$$?

Accepted Answer

$$\mathrm{O_2$}$$ has unpaired electrons in the $$\pi^*$$ orbitals

Question 20

Which of the following statements about hybridization is correct for $$\mathrm{$$SiH_3$$^+}$$?

Accepted Answer

$$\mathrm{$$SiH_3$$^+}$$ has an unoccupied $$sp^2$$ hybrid orbital

Molecular Orbitals, Lewis Acids, and Bond Rotation: General Chemistry Study Notes

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