Q: Which of the following is the correct formula for calculating the formal charge (FC) on an atom in a Lewis structure?

$\mathrm{FC = \#\ valence\ e^- - (\#\ non\text{-}bonding\ e^- + \frac{1}{2}\ \#\ bonding\ e^-)}$

Question 1

Which of the following best explains why chemical bonds form between atoms?

Accepted Answer

Because chemical bonds lower the potential energy between charged particles that compose the atoms.

Question 2

Which of the following statements about the octet rule is correct?

Accepted Answer

Hydrogen is stable with two valence electrons, while most other nonmetals are stable with eight.

Question 3

Which of the following best describes metallic bonding?

Accepted Answer

Valence electrons are pooled and delocalized over a lattice of metal cations.

Question 4

Consider the Lewis structure for the carbonate ion, $\mathrm{CO_3^{2-}}$. Which statement is true regarding its resonance structures?

Accepted Answer

The actual structure is a resonance hybrid, with the double bond delocalized over all three oxygen atoms.

Question 5

Which of the following is the correct formula for calculating the formal charge (FC) on an atom in a Lewis structure?

Accepted Answer

$\mathrm{FC = \#\ valence\ e^- - (\#\ non	ext{-}bonding\ e^- + \frac{1}{2}\ \#\ bonding\ e^-)}$

Question 6

Which of the following molecules is an example of an exception to the octet rule due to an incomplete octet?

Accepted Answer

$\mathrm{BF_3}$

Question 7

Which of the following best describes the trend in lattice energy for ionic compounds?

Accepted Answer

Lattice energy increases with larger charges and decreases with larger ions.

Question 8

Given the following reaction: $\mathrm{CH_4(g) + Cl_2(g) \rightarrow CH_3Cl(g) + HCl(g)}$, and the following average bond energies: $\mathrm{BE(C-H) = 414\ kJ\ mol^{-1}}$, $\mathrm{BE(Cl-Cl) = 243\ kJ\ mol^{-1}}$, $\mathrm{BE(C-Cl) = 339\ kJ\ mol^{-1}}$, $\mathrm{BE(H-Cl) = 431\ kJ\ mol^{-1}}$, what is the estimated enthalpy change ($\Delta H$) for the reaction?

Accepted Answer

$\Delta H = [(414) + (243)] - [(339) + (431)] = -113\ \mathrm{kJ\ mol^{-1}}$

Question 9

Which of the following statements about bond order, bond length, and bond energy is correct?

Accepted Answer

As bond order increases, bond length decreases and bond energy increases.

Question 10

Which of the following best describes the difference between a polar covalent bond and a nonpolar covalent bond?

Accepted Answer

A polar covalent bond involves unequal sharing of electrons due to a difference in electronegativity, while a nonpolar covalent bond involves equal sharing.

Question 11

Which of the following is a correct statement about resonance structures?

Accepted Answer

Resonance structures are a way to represent delocalized electrons within a molecule where the actual structure is a hybrid of all possible resonance forms.

Question 12

Which of the following ions is an example of a hypercoordinate compound?

Accepted Answer

$\mathrm{SO_4^{2-}}$

Question 13

Which of the following best describes the Born-Haber cycle?

Accepted Answer

It is a series of hypothetical steps used to calculate the lattice energy of an ionic compound from its elements.

Question 14

Which of the following molecules is a free radical due to having an odd number of electrons?

Accepted Answer

$\mathrm{NO}$

Question 15

Which of the following statements about electronegativity is correct?

Accepted Answer

Electronegativity increases across a period and decreases down a group.

Question 16

Which of the following is the most stable Lewis structure for $\mathrm{BF_3}$?

Accepted Answer

A structure where boron has an incomplete octet and all formal charges are zero.

Question 17

Which of the following best explains why the actual enthalpy of formation for $\mathrm{NaCl(s)}$ is much more exothermic than the difference between the ionization energy of Na and the electron affinity of Cl?

Accepted Answer

Because the formation of the ionic lattice releases a large amount of lattice energy.

Question 18

Which of the following statements about bond vibrations is correct?

Accepted Answer

A higher bond energy corresponds to a higher vibrational frequency.

Question 19

Which of the following is the best Lewis structure for the sulfate ion, $\mathrm{SO_4^{2-}}$, based on formal charges?

Accepted Answer

A structure with two double bonds to oxygen and two single bonds, where the double-bonded oxygens have formal charge zero and the single-bonded oxygens have formal charge $-1$.

Chemical Bonding I: Lewis Theory – Structured Study Notes

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