Lewis Structures & Resonance practice questions

Question 1

A student is asked to draw a Lewis diagram for the chlorate ion, $\text{ClO}_3^-$, that satisfies the octet rule for all constituent atoms. Which of the following diagrams correctly represents a valid Lewis structure for $\text{ClO}_3^-$?

Accepted Answer

Diagram D

Answer

Diagram A

Answer

Diagram B

Answer

Diagram C

Question 2

Which of the following correctly identifies the molecular geometry and the hybridization of the central atom in a molecule of $\text{XeF}_4$?

Accepted Answer

Square planar and $sp^3d^2$

Answer

Square planar and $sp^3d$

Answer

Tetrahedral and $sp^3$

Answer

See-saw and $sp^3d$

Question 3

A student draws a Lewis structure for the carbonate ion, $\text{CO}_3^{2-}$, showing one carbon-oxygen double bond and two carbon-oxygen single bonds. Experimental measurements show that all three carbon-oxygen bond lengths in $\text{CO}_3^{2-}$ are identical ($128\text{ pm}$). Which of the following statements correctly identifies the bond order and justifies the equal bond lengths in $\text{CO}_3^{2-}$?

Accepted Answer

All three $\text{C}-\text{O}$ bonds have equal length and a bond order of $1.33$ because the $\pi$ electrons are delocalized equally across all three carbon-oxygen bonds.

Answer

One $\text{C}-\text{O}$ bond is shorter than the other two because double bonds have higher bond orders and shorter bond lengths than single bonds.

Answer

All three $\text{C}-\text{O}$ bonds have equal length and a bond order of $1.33$ because the carbon atom rapidly alternates forming a double bond with each of the three oxygen atoms.

Answer

All three $\text{C}-\text{O}$ bonds have equal length and a bond order of $1.00$ because single bonds form between carbon and each oxygen atom to minimize electron-electron repulsion.

Question 4

A student is asked to select the Lewis diagram for sulfur dioxide, $\text{SO}_2$, that represents the most favorable formal-charge arrangement. Which of the following diagrams correctly represents this structure?

Accepted Answer

Structure C

Answer

Structure A

Answer

Structure B

Answer

Structure D

Question 5

A student compares the following Lewis structures for nitrous oxide, $\text{N}_2\text{O}$, which has the atom connectivity $\text{N}-\text{N}-\text{O}$.

Structure I: $\text{N}\equiv\text{N}-\text{O}$, with one lone pair on the terminal nitrogen atom, no lone pairs on the central nitrogen atom, and three lone pairs on the oxygen atom.

Structure II: $\text{N}=\text{N}=\text{O}$, with two lone pairs on the terminal nitrogen atom, no lone pairs on the central nitrogen atom, and two lone pairs on the oxygen atom.

Each structure uses 16 valence electrons and gives every atom an octet. Which statement correctly identifies the favored Lewis structure and justifies the choice using formal charges?

Accepted Answer

Structure I is favored. Its formal charges on the terminal nitrogen, central nitrogen, and oxygen atoms are $0$, $+1$, and $-1$, respectively, because the negative formal charge is located on the more electronegative atom.

Answer

Structure II is favored. Its formal charges on the terminal nitrogen, central nitrogen, and oxygen atoms are $-1$, $+1$, and $0$, respectively, because avoiding a negative formal charge on oxygen produces the more favorable structure.

Answer

Structure II is favored. Its formal charges on the terminal nitrogen, central nitrogen, and oxygen atoms are all $0$, so it is favored because it has no charge separation.

Answer

Structure I is favored. Its formal charges on the terminal nitrogen, central nitrogen, and oxygen atoms are $0$, $+1$, and $-1$, respectively, because a structure containing a triple bond is always favored over one containing two double bonds.

Question 6

A student draws the Lewis diagram shown below for xenon tetrafluoride ($\text{XeF}_4$). Which of the following claims best describes the predicted $\text{F}-\text{Xe}-\text{F}$ bond angles in $\text{XeF}_4$ and provides the correct justification?

Accepted Answer

The $\text{F}-\text{Xe}-\text{F}$ bond angles are equal to $90^\circ$ because the two lone pairs on the central $\text{Xe}$ atom occupy positions $180^\circ$ apart, exerting symmetrical repulsions above and below the square plane.

Answer

The $\text{F}-\text{Xe}-\text{F}$ bond angles are less than $90^\circ$ because lone pair-bonding pair repulsions are stronger than bonding pair-bonding pair repulsions, compressing the bonds toward each other.

Answer

The $\text{F}-\text{Xe}-\text{F}$ bond angles are less than $90^\circ$ because six electron domains around the central $\text{Xe}$ atom create steric crowding that distorts the square planar geometry.

Answer

The $\text{F}-\text{Xe}-\text{F}$ bond angles are equal to $90^\circ$ because the central $\text{Xe}$ atom forms four equivalent bonds with zero lone pairs in its valence shell.

Question 7

A student compares two structural models for benzene, $\text{C}_6\text{H}_6$, as shown in the diagram: Model 1 with localized alternating single and double carbon-carbon bonds, and Model 2 with a delocalized resonance hybrid. Which of the following experimental observations provides the best evidence supporting Model 2 over Model 1?

Accepted Answer

All six carbon-carbon bonds have an identical measured length of $139\text{ pm}$, which is intermediate between a standard $\text{C}-\text{C}$ single bond ($154\text{ pm}$) and a standard $\text{C}=\text{C}$ double bond ($134\text{ pm}$).

Answer

Benzene reacts with hydrogen gas in the presence of a metal catalyst to form cyclohexane, $\text{C}_6\text{H}_{12}$, consuming three moles of $\text{H}_2$ for every one mole of benzene reacted.

Answer

The six carbon atoms in the ring lie in a single geometric plane with bond angles of $120^\circ$, consistent with $sp^2$ hybridization at each carbon atom.

Answer

Elemental analysis shows that benzene consists of $92.3\%$ carbon and $7.7\%$ hydrogen by mass, establishing an empirical formula of $\text{CH}$.

Question 8

A student is asked to draw a valid Lewis electron-dot diagram for a molecule of bromine trifluoride, $\text{BrF}_3$. Which of the following diagrams represents the correct Lewis structure for $\text{BrF}_3$?

Accepted Answer

Diagram C

Answer

Diagram A

Answer

Diagram B

Answer

Diagram D

Question 9

The sulfate ion, $\text{SO}_4^{2-}$, is a polyatomic anion commonly found in various mineral salts. Which of the following Lewis diagrams represents the most favorable formal-charge arrangement for $\text{SO}_4^{2-}$?

Accepted Answer

Diagram C

Answer

Diagram A

Answer

Diagram B

Answer

Diagram D

Question 10

Fluoroacetic acid, $\text{CH}_2\text{FCOOH}$, is a stronger acid than chloroacetic acid, $\text{CH}_2\text{ClCOOH}$, because the higher electronegativity of fluorine stabilizes the conjugate base through an inductive effect. Which of the following complete Lewis diagrams for the fluoroacetate ion, $\text{CH}_2\text{FCO}_2^-$, correctly shows all valence electrons and formal charges?

Accepted Answer

Diagram C

Answer

Diagram A

Answer

Diagram B

Answer

Diagram D

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