Chemical Bonding — Practice Quiz

A Chemistry cheat sheet for Chemical Bonding — every key formula with its symbols defined — plus a medium-level practice quiz to test recall.

Formulas & key concepts

Electrostatic Potential Energy: Energy of interaction between two charged particles.

$$E_{\text{el}} = \frac{kQ_1Q_2}{d}$$

Where: k = Coulomb's constant (8.99 × 10<sup>9</sup> J·m/C<sup>2</sup>), Q = charges, d = distance

Dipole Moment: Measure of charge separation in a molecule.

$$\mu = Qr$$

Where: Q = magnitude of charge, r = distance between charges

Enthalpy from Bond Enthalpies: Estimate reaction enthalpy using bond energies.

$$\Delta H_{\text{rxn}} = \sum (\text{enthalpies broken}) - \sum (\text{enthalpies formed})$$

Where: For gas-phase reactions only

<table style="width:100%; border-collapse: collapse; font-size: 0.85em;"> <tr style="border-bottom: 1px solid #ccc;"><th>Group</th><th>Element</th><th>Configuration</th><th>Lewis Symbol</th></tr> <tr><td>1A</td><td>Li</td><td>[He] 2s<sup>1</sup></td><td>Li·</td></tr> <tr><td>2A</td><td>Be</td><td>[He] 2s<sup>2</sup></td><td>:Be:</td></tr> <tr><td>3A</td><td>B</td><td>[He] 2s<sup>2</sup> 2p<sup>1</sup></td><td>·B·</td></tr> <tr><td>4A</td><td>C</td><td>[He] 2s<sup>2</sup> 2p<sup>2</sup></td><td>:C::</td></tr> <tr><td>5A</td><td>N</td><td>[He] 2s<sup>2</sup> 2p<sup>3</sup></td><td>:N::·</td></tr> <tr><td>6A</td><td>O</td><td>[He] 2s<sup>2</sup> 2p<sup>4</sup></td><td>:O::</td></tr> <tr><td>7A</td><td>F</td><td>[He] 2s<sup>2</sup> 2p<sup>5</sup></td><td>:F:··</td></tr> <tr><td>8A</td><td>Ne</td><td>[He] 2s<sup>2</sup> 2p<sup>6</sup></td><td>:Ne::</td></tr> </table>

$$\text{Lewis Symbols}$$

Bond Order: Half the difference between the number of bonding electrons and antibonding electrons.

$$\text{Bond Order} = \frac{1}{2} (N_b - N_a)$$

Where: N<sub>b</sub> = number of bonding electrons, N<sub>a</sub> = number of antibonding electrons

<table style="width:100%; border-collapse: collapse; font-size: 0.85em;"> <thead> <tr style="border-bottom: 2px solid #444;"> <th style="padding: 4px; text-align: left;">Bond</th> <th style="padding: 4px; text-align: left;">D (kJ/mol)</th> <th style="padding: 4px; text-align: left;">Bond</th> <th style="padding: 4px; text-align: left;">D (kJ/mol)</th> </tr> </thead> <tbody> <tr><td style="padding: 2px;">C-H</td><td style="padding: 2px;">413</td><td style="padding: 2px;">C-C</td><td style="padding: 2px;">348</td></tr> <tr><td style="padding: 2px;">C-N</td><td style="padding: 2px;">293</td><td style="padding: 2px;">C-O</td><td style="padding: 2px;">358</td></tr> <tr><td style="padding: 2px;">C-F</td><td style="padding: 2px;">485</td><td style="padding: 2px;">C-Cl</td><td style="padding: 2px;">328</td></tr> <tr><td style="padding: 2px;">C-Br</td><td style="padding: 2px;">276</td><td style="padding: 2px;">C-I</td><td style="padding: 2px;">240</td></tr> <tr><td style="padding: 2px;">C-S</td><td style="padding: 2px;">259</td><td style="padding: 2px;">Si-H</td><td style="padding: 2px;">323</td></tr> <tr><td style="padding: 2px;">Si-Si</td><td style="padding: 2px;">226</td><td style="padding: 2px;">Si-C</td><td style="padding: 2px;">301</td></tr> <tr><td style="padding: 2px;">Si-O</td><td style="padding: 2px;">368</td><td style="padding: 2px;">N-H</td><td style="padding: 2px;">391</td></tr> <tr><td style="padding: 2px;">N-N</td><td style="padding: 2px;">163</td><td style="padding: 2px;">N-O</td><td style="padding: 2px;">201</td></tr> <tr><td style="padding: 2px;">N-F</td><td style="padding: 2px;">272</td><td style="padding: 2px;">N-Cl</td><td style="padding: 2px;">200</td></tr> <tr><td style="padding: 2px;">N-Br</td><td style="padding: 2px;">243</td><td style="padding: 2px;">H-H</td><td style="padding: 2px;">436</td></tr> <tr><td style="padding: 2px;">H-F</td><td style="padding: 2px;">567</td><td style="padding: 2px;">H-Cl</td><td style="padding: 2px;">431</td></tr> <tr><td style="padding: 2px;">H-Br</td><td style="padding: 2px;">366</td><td style="padding: 2px;">H-I</td><td style="padding: 2px;">299</td></tr> <tr><td style="padding: 2px;">O-H</td><td style="padding: 2px;">463</td><td style="padding: 2px;">O-O</td><td style="padding: 2px;">146</td></tr> <tr><td style="padding: 2px;">O-F</td><td style="padding: 2px;">190</td><td style="padding: 2px;">O-Cl</td><td style="padding: 2px;">203</td></tr> <tr><td style="padding: 2px;">O-I</td><td style="padding: 2px;">234</td><td style="padding: 2px;">S-H</td><td style="padding: 2px;">339</td></tr> <tr><td style="padding: 2px;">S-F</td><td style="padding: 2px;">327</td><td style="padding: 2px;">S-Cl</td><td style="padding: 2px;">253</td></tr> <tr><td style="padding: 2px;">S-Br</td><td style="padding: 2px;">218</td><td style="padding: 2px;">S-S</td><td style="padding: 2px;">266</td></tr> <tr style="border-top: 1px solid #666;"><td colspan="4" style="padding: 4px; font-weight: bold; text-align: center;">Multiple Bonds</td></tr> <tr><td style="padding: 2px;">C=C</td><td style="padding: 2px;">614</td><td style="padding: 2px;">C≡C</td><td style="padding: 2px;">839</td></tr> <tr><td style="padding: 2px;">C=N</td><td style="padding: 2px;">615</td><td style="padding: 2px;">C≡N</td><td style="padding: 2px;">891</td></tr> <tr><td style="padding: 2px;">C=O</td><td style="padding: 2px;">799</td><td style="padding: 2px;">C≡O</td><td style="padding: 2px;">1072</td></tr> <tr><td style="padding: 2px;">N=N</td><td style="padding: 2px;">418</td><td style="padding: 2px;">N≡N</td><td style="padding: 2px;">941</td></tr> <tr><td style="padding: 2px;">O=O</td><td style="padding: 2px;">495</td><td style="padding: 2px;">S=O</td><td style="padding: 2px;">523</td></tr> <tr><td style="padding: 2px;">S=S</td><td style="padding: 2px;">418</td><td style="padding: 2px;"></td><td style="padding: 2px;"></td></tr> </tbody> </table>

$$\text{Average Bond Enthalpies}$$

<table style="width:100%; border-collapse: collapse; font-size: 0.85em;"> <thead> <tr style="border-bottom: 2px solid #444;"> <th style="padding: 4px; text-align: left;">Bond</th> <th style="padding: 4px; text-align: left;">Length (Å)</th> <th style="padding: 4px; text-align: left;">Bond</th> <th style="padding: 4px; text-align: left;">Length (Å)</th> </tr> </thead> <tbody> <tr><td style="padding: 2px;">C-H</td><td style="padding: 2px;">1.09</td><td style="padding: 2px;">C-C</td><td style="padding: 2px;">1.54</td></tr> <tr><td style="padding: 2px;">C=C</td><td style="padding: 2px;">1.34</td><td style="padding: 2px;">C≡C</td><td style="padding: 2px;">1.20</td></tr> <tr><td style="padding: 2px;">C-O</td><td style="padding: 2px;">1.43</td><td style="padding: 2px;">C=O</td><td style="padding: 2px;">1.21</td></tr> <tr><td style="padding: 2px;">C-N</td><td style="padding: 2px;">1.47</td><td style="padding: 2px;">C=N</td><td style="padding: 2px;">1.28</td></tr> <tr><td style="padding: 2px;">C≡N</td><td style="padding: 2px;">1.16</td><td style="padding: 2px;">N-O</td><td style="padding: 2px;">1.40</td></tr> <tr><td style="padding: 2px;">N=O</td><td style="padding: 2px;">1.20</td><td style="padding: 2px;">O-H</td><td style="padding: 2px;">0.96</td></tr> </tbody> </table>

$$\text{Average Bond Lengths}$$

Practice quiz

  1. Calculate the electrostatic potential energy between two ions, $Q_1 = +2e$ and $Q_2 = -1e$, separated by a distance of $0.25 \text{ nm}$. Use $k = 8.99 \times 10^9 \text{ J} \cdot \text{m/C}^2$ and $e = 1.602 \times 10^{-19} \text{ C}$.

    • $-1.84 \times 10^{-18} \text{ J}$
    • $1.84 \times 10^{-18} \text{ J}$
    • $-3.68 \times 10^{-18} \text{ J}$
    • $3.68 \times 10^{-18} \text{ J}$

    Answer: $-1.84 \times 10^{-18} \text{ J}$

  2. How does the electrostatic potential energy $E_{\text{el}}$ between two oppositely charged ions change if the distance $d$ between them is doubled?

    • It becomes half as negative (closer to zero).
    • It becomes twice as negative.
    • It remains the same.
    • It becomes four times as negative.

    Answer: It becomes half as negative (closer to zero).

  3. A molecule has a charge separation of $1.5 \times 10^{-19} \text{ C}$ and the distance between the separated charges is $1.2 \text{ \AA}$. Calculate its dipole moment $\mu$.

    • $1.8 \times 10^{-29} \text{ C} \cdot \text{m}$
    • $1.8 \times 10^{-30} \text{ C} \cdot \text{m}$
    • $1.25 \times 10^{-9} \text{ C} \cdot \text{m}$
    • $1.25 \times 10^{-10} \text{ C} \cdot \text{m}$

    Answer: $1.8 \times 10^{-29} \text{ C} \cdot \text{m}$

  4. Which of the following factors would lead to an increase in the dipole moment $\mu$ of a diatomic molecule?

    • Decreasing the magnitude of the separated charges.
    • Increasing the distance between the separated charges.
    • Making the molecule more symmetrical.
    • Decreasing the electronegativity difference between the atoms.

    Answer: Increasing the distance between the separated charges.

  5. Estimate the enthalpy change $\Delta H_{\text{rxn}}$ for the reaction: $2\text{H}_2(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{H}_2\text{O}(\text{g})$ using the provided average bond enthalpies. (H-H: $436 \text{ kJ/mol}$, O=O: $495 \text{ kJ/mol}$, O-H: $463 \text{ kJ/mol}$)

    • $-485 \text{ kJ/mol}$
    • $485 \text{ kJ/mol}$
    • $-242.5 \text{ kJ/mol}$
    • $242.5 \text{ kJ/mol}$

    Answer: $-485 \text{ kJ/mol}$

  6. The formula for $\Delta H_{\text{rxn}}$ using bond enthalpies is most accurate for which type of reactions?

    • Reactions involving solids and liquids.
    • Reactions occurring in aqueous solutions.
    • Gas-phase reactions.
    • Reactions at very low temperatures.

    Answer: Gas-phase reactions.

  7. According to the provided Lewis Symbols table, which of the following is the correct Lewis symbol for a Nitrogen atom?

    • :N::\cdot
    • :N::
    • \cdot N \cdot
    • :N:

    Answer: :N::\cdot

  8. What is the bond order for the carbon-oxygen bond in carbon monoxide, $\text{CO}$?

    • $1$
    • $2$
    • $3$
    • $2.5$

    Answer: $3$

  9. Based on the provided tables, which statement is true regarding carbon-carbon bonds?

    • A $\text{C-C}$ single bond is stronger and shorter than a $\text{C=C}$ double bond.
    • A $\text{C=C}$ double bond is stronger and shorter than a $\text{C\equiv C}$ triple bond.
    • A $\text{C\equiv C}$ triple bond is stronger and shorter than a $\text{C=C}$ double bond.
    • All carbon-carbon bonds have approximately the same strength and length.

    Answer: A $\text{C\equiv C}$ triple bond is stronger and shorter than a $\text{C=C}$ double bond.

  10. Consider the $\text{C-O}$ bond. How does its bond enthalpy and bond length compare to a $\text{C=O}$ bond?

    • $\text{C-O}$ has a higher bond enthalpy and a shorter bond length than $\text{C=O}$.
    • $\text{C-O}$ has a lower bond enthalpy and a longer bond length than $\text{C=O}$.
    • $\text{C-O}$ has a higher bond enthalpy and a longer bond length than $\text{C=O}$.
    • $\text{C-O}$ has a lower bond enthalpy and a shorter bond length than $\text{C=O}$.

    Answer: $\text{C-O}$ has a lower bond enthalpy and a longer bond length than $\text{C=O}$.

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