Question 1

Which of the following molecules has the largest dipole moment, and why?
Correct answer: H2O, because oxygen is the most electronegative and the molecule is bent

Accepted Answer

H2O, because oxygen is the most electronegative and the molecule is bent

Question 2

An unknown element has a Lewis symbol with six dots around it. Which group does it belong to, and what is a likely chemical property?
Correct answer: Group 6A; it tends to gain two electrons to form a -2 anion

Accepted Answer

Group 6A; it tends to gain two electrons to form a -2 anion

Question 3

Given the ionic radii of Mg2+ (0.86 Å) and O2- (1.26 Å), what is the estimated distance between their nuclei in MgO, and what does this value represent?
Correct answer: 2.12 Å; the sum of the ionic radii, representing the distance between cation and anion centers

Accepted Answer

2.12 Å; the sum of the ionic radii, representing the distance between cation and anion centers

Question 4

Which of the following pairs are isoelectronic?
Correct answer: O2- and F-

Accepted Answer

O2- and F-

Question 5

A polyatomic oxyanion contains a period 4 central atom. If the overall charge of the ion increases by one, what happens to the formal charge on the central atom?
Correct answer: It becomes more negative by one unit

Accepted Answer

It becomes more negative by one unit

Question 6

Which of the following Lewis structures for HNO3 is preferred?
Correct answer: The one in which all atoms obey the octet rule

Accepted Answer

The one in which all atoms obey the octet rule

Question 7

Which of the following bonds has the least covalent character?
Correct answer: CuF

Accepted Answer

CuF

Question 8

Why can elements in the third period and beyond form expanded octets?
Correct answer: They have available d orbitals to accommodate extra electrons

Accepted Answer

They have available d orbitals to accommodate extra electrons

Question 9

Rank the following molecules in order of increasing C–C bond strength: H2NCH2CH2NH2, H2NCHCHNH2, H2NCCNH2.
Correct answer: H2NCH2CH2NH2 \u003c H2NCHCHNH2 \u003c H2NCCNH2

Accepted Answer

H2NCH2CH2NH2 \u003c H2NCHCHNH2 \u003c H2NCCNH2

Question 10

Which statement about resonance structures is correct?
Correct answer: They represent delocalization of electrons, and the true structure is a hybrid of all resonance forms

Accepted Answer

They represent delocalization of electrons, and the true structure is a hybrid of all resonance forms

Question 11

In the Lewis structure of PHF2, how many lone pairs are on the central atom, and how many double bonds are present?
Correct answer: 1 lone pair, 0 double bonds

Accepted Answer

1 lone pair, 0 double bonds

Question 12

A reaction has a negative enthalpy change (ΔH \u003c 0) when calculated using bond enthalpies. What does this indicate about the reaction?
Correct answer: The reaction is exothermic; more energy is released forming bonds than is required to break them

Accepted Answer

The reaction is exothermic; more energy is released forming bonds than is required to break them

Question 13

Which of the following best explains why the bond in CuF is less covalent than in CuI?
Correct answer: The difference in electronegativity between Cu and F is greater than between Cu and I

Accepted Answer

The difference in electronegativity between Cu and F is greater than between Cu and I

Question 14

If a molecule violates the octet rule for a main group element, what is the most likely reason?
Correct answer: The element is in period 3 or higher and can have an expanded octet

Accepted Answer

The element is in period 3 or higher and can have an expanded octet

Question 15

Which of the following is a correct application of the formal charge formula FC = V – N – B/2?
Correct answer: For an oxygen atom with 6 valence electrons, 4 nonbonding electrons, and 2 bonds: FC = 6 – 4 – 2 = 0

Accepted Answer

For an oxygen atom with 6 valence electrons, 4 nonbonding electrons, and 2 bonds: FC = 6 – 4 – 2 = 0

Question 16

A chemist is designing a new ionic compound using Ca2+ and S2-. What is the estimated distance between the cation and anion centers?
Correct answer: 2.84 Å

Accepted Answer

2.84 Å

Question 17

Which of the following best describes the direction of the dipole moment in H2S?
Correct answer: Toward the sulfur atom, because it is more electronegative than hydrogen

Accepted Answer

Toward the sulfur atom, because it is more electronegative than hydrogen

Question 18

Which of the following statements about resonance in N2O4 is correct?
Correct answer: Resonance structures show delocalization of electrons, not movement of atoms

Accepted Answer

Resonance structures show delocalization of electrons, not movement of atoms

Question 19

Which of the following is NOT a reason why the octet rule might be violated in a Lewis structure?
Correct answer: The central atom is from period 2 and forms more than four bonds

Accepted Answer

The central atom is from period 2 and forms more than four bonds

Key Concepts in Chemical Bonding, Structure, and Energetics

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