Q: Which of the following statements about resonance structures is TRUE?

The actual structure of a molecule with resonance is a weighted average of all valid resonance forms.

Q: Which of the following best explains why the Lewis structure for $\mathrm{SF_6}$ violates the octet rule?

Sulfur is a third-row element and can expand its octet to accommodate more than 8 electrons.

Q: Which of the following statements about lattice energy is correct?

Lattice energy becomes more exothermic as the charges on the ions increase and the ionic radii decrease.

Q: Which of the following statements about electronegativity is FALSE?

Electronegativity values are highest for alkali metals.

Q: Which of the following best describes the relationship between bond order and bond length for a given pair of atoms?

As bond order increases, bond length decreases.

Q: Which of the following is a correct application of the octet rule exception for a molecule?

Boron in $\mathrm{BF_3}$ can have only 6 electrons in its valence shell.

Q: Which of the following best explains why the Born-Haber cycle is used in chemistry?

To estimate the lattice energy of an ionic compound using known enthalpy values and Hess's law.

Question 1

Which of the following statements best explains why ionic compounds such as NaCl have high melting points?

Accepted Answer

Because the ions are fixed in a crystalline lattice with strong electrostatic attractions between oppositely charged ions.

Question 2

Which of the following molecules contains an atom that does NOT have a complete octet in its Lewis structure?

Accepted Answer

BH3

Question 3

How many total valence electrons are present in a molecule of acetone, $\mathrm{C_3H_6O}$?

Accepted Answer

$24$

Question 4

Which of the following best describes the difference between an ionic bond and a covalent bond?

Accepted Answer

Ionic bonds involve the transfer of electrons from a metal to a nonmetal, while covalent bonds involve the sharing of electrons between two nonmetals.

Question 5

Which of the following steps is NOT part of the general procedure for drawing a Lewis structure for a simple molecule?

Accepted Answer

Assign formal charges to each atom before distributing electrons.

Question 6

Which of the following correctly ranks the compounds LiBr, KI, and CaO in order of increasing magnitude of lattice energy?

Accepted Answer

LiBr < KI < CaO

Question 7

A molecule of carbon dioxide, $\mathrm{CO_2}$, has which of the following Lewis structures?

Accepted Answer

$\mathrm{O=C=O}$

Question 8

Which of the following statements about resonance structures is TRUE?

Accepted Answer

The actual structure of a molecule with resonance is a weighted average of all valid resonance forms.

Question 9

Which of the following best explains why the Lewis structure for $\mathrm{SF_6}$ violates the octet rule?

Accepted Answer

Sulfur is a third-row element and can expand its octet to accommodate more than 8 electrons.

Question 10

Which of the following bonds is expected to be the most polar?

Accepted Answer

$\mathrm{H-F}$

Question 11

Given the following reaction: $\mathrm{CH_4 + 2H_2O \rightarrow 4H_2 + CO_2}$, and the following bond energies: $\mathrm{C-H = 414\ kJ/mol}$, $\mathrm{O-H = 463\ kJ/mol}$, $\mathrm{H-H = 436\ kJ/mol}$, $\mathrm{C=O = 799\ kJ/mol}$, what is the enthalpy change $\Delta H$ for the reaction?

Accepted Answer

$-206\ \mathrm{kJ/mol}$

Question 12

Which of the following is the correct formal charge on the nitrogen atom in the Lewis structure of $\mathrm{NH_4^+}$?

Accepted Answer

$0$

Question 13

Which of the following statements about lattice energy is correct?

Accepted Answer

Lattice energy becomes more exothermic as the charges on the ions increase and the ionic radii decrease.

Question 14

Which of the following species is a free radical?

Accepted Answer

$\mathrm{NO}$

Question 15

Which of the following is the best Lewis structure for the cyanate ion, $\mathrm{OCN^-}$, based on formal charges?

Accepted Answer

$[\mathrm{O=C=N^-}]$

Question 16

Which of the following statements about electronegativity is FALSE?

Accepted Answer

Electronegativity values are highest for alkali metals.

Question 17

Which of the following best describes the relationship between bond order and bond length for a given pair of atoms?

Accepted Answer

As bond order increases, bond length decreases.

Question 18

Which of the following is a correct application of the octet rule exception for a molecule?

Accepted Answer

Boron in $\mathrm{BF_3}$ can have only 6 electrons in its valence shell.

Question 19

Which of the following best explains why the Born-Haber cycle is used in chemistry?

Accepted Answer

To estimate the lattice energy of an ionic compound using known enthalpy values and Hess's law.

Chapter 9: Chemical Bonding I – Lewis Structures and Bond Energies

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