Question 1

Which atomic orbital has the greatest number of nodes, and what is the relationship between the principal quantum number $n$ and the number of nodes in an $s$ orbital?

Accepted Answer

The 3s orbital; the number of nodes is $n-1$.

Question 2

According to the energy diagram for the hydrogen molecule, what happens to the energy of the system as two hydrogen atoms approach each other too closely?

Accepted Answer

The energy increases due to strong repulsive forces.

Question 3

Which atomic orbitals are mixed to produce the $sp^3$ hybridized orbitals in methane ($CH_4$)?

Accepted Answer

One $s$ and three $p$ orbitals.

Question 4

In the molecule $CH_3COCH_2C\equiv CH$, what is the hybridization of the carbon atom labeled as #3?

Accepted Answer

sp^3

Question 5

Which statement best describes the bond angles and hybridization in ethyne ($C_2H_2$)?

Accepted Answer

Bond angles are 180°, and carbons are $sp$ hybridized.

Question 6

Which of the following best explains why the C-H bond in ethyne is stronger than in ethene?

Accepted Answer

The $sp$ hybridized orbital in ethyne has more $s$ character, leading to greater overlap.

Question 7

According to molecular orbital (MO) theory, what is the result of the constructive interference of two $1s$ atomic orbitals?

Accepted Answer

Formation of a $	ext{σ}$ bonding orbital.

Question 8

In the MO diagram for $H_2$, which orbital is the highest in energy?

Accepted Answer

$\sigma^*_{1s}$ antibonding orbital

Question 9

Which of the following free radicals can have the most resonance forms showing delocalization of the radical?

Accepted Answer

Benzyl radical

Question 10

Which of the following carbocations is most stabilized by resonance?

Accepted Answer

A carbocation adjacent to a benzene ring (benzylic carbocation)

Question 11

Which principle is most important when determining the major resonance contributor for a molecule?

Accepted Answer

The structure in which all atoms obey the octet rule.

Question 12

What is the condition for conjugation in a molecule according to MO theory?

Accepted Answer

Three or more parallel $p$ orbitals on adjacent atoms.

Question 13

Which of the following statements about resonance contributors is FALSE?

Accepted Answer

Resonance contributors can violate the octet rule for second row elements.

Question 14

In the context of resonance, what is the significance of an allylic lone pair?

Accepted Answer

It allows for delocalization of electrons over three atoms.

Question 15

Which hybridization is required for a second row atom to form a $\pi$ bond?

Accepted Answer

A $p$ orbital

Question 16

Which of the following is NOT a criterion for an insignificant resonance contributor?

Accepted Answer

All atoms have complete octets and minimal formal charge.

Question 17

Which of the following molecules contains a conjugated carbocation?

Accepted Answer

A carbocation adjacent to a double bond (allylic carbocation)

Question 18

What is the effect of conjugation on the stability of a molecule?

Accepted Answer

It stabilizes the molecule by delocalizing electrons.

Question 19

Which of the following best describes the difference between valence bond theory and molecular orbital theory?

Accepted Answer

Valence bond theory describes electrons as localized between atoms, while MO theory describes electrons as delocalized over the whole molecule.

Bonding and Electronic Structure in Organic Molecules

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