08 Lewis Structures and Resonance Online Quiz Questions

Construct the Lewis structure of CO2 by showing how the electron count leads from an O–C–O single-bond skeleton to the final structure. Account for the electrons at each stage and verify the shells and formal charges.

A proposed Lewis structure for NH4+ has nitrogen central with four N–H single bonds. Determine its total valence-electron count, nitrogen's formal charge, the hydrogens' formal charges, and whether the formal-charge sum matches the ion's charge. Show your reasoning.

A student proposes that every valence electron in NO is paired. Calculate the molecule's valence-electron total and explain whether that proposal can be correct without changing the electron count.

Compare the common Lewis representations of BF3 and BeH2. How many shared electrons are around each central atom, what octet-rule exception do they illustrate, and what mistaken adjustment might a student make by treating the octet rule as universal?

Explain what information a Lewis structure can represent and what it cannot be taken to show literally. Include the meanings of both lines and dots in your explanation.

Three proposed Lewis structures describe the same species. Candidate A gives every second-period atom an octet, has small formal-charge magnitudes, and places negative formal charge on oxygen. Candidate B gives every second-period atom an octet but has larger formal-charge magnitudes and puts negative formal charge on a less electronegative atom. Candidate C has smaller formal-charge magnitudes than B but leaves a second-period central atom without an octet. Which candidate is best supported by the structure-selection guidelines, and what can and cannot be concluded about the other two from the information given?

A classmate argues that an atom with formal charge zero must have no actual charge in the molecule. Explain the reasoning behind formal charge and why that conclusion does not follow.

For nitrite, NO2−, determine the total number of valence electrons and describe its two equivalent resonance contributors. For each contributor, state the lone-pair pattern and formal charges, verify the overall charge, and explain what the equivalence implies for the two N–O bonds in the hybrid.

A proposed alternative drawing of a polyatomic ion has the same total electron count and overall charge as the original, but one atom has been moved to a different position in the skeleton. Is the alternative a resonance form? Explain which requirements it meets and which requirement it violates.

A student describes a species with equivalent resonance contributors as rapidly switching between separate structures, one with a single bond and one with a double bond. Correct the explanation and state what the bond description should represent instead.

A proposed resonance contributor for an ion with overall charge $-1$ has formal charges that sum to zero. Its author has not established whether it has the same total number of electrons as the original contributor. Explain what this information establishes, what remains to be checked before the proposal can be accepted as a resonance contributor, and how to perform that check. Include the requirement for atom positions.

Develop a step-by-step workflow for constructing a Lewis structure of an unfamiliar polyatomic ion. Explain how the ion's charge affects the initial count, how electrons are distributed, when multiple bonds may be considered, and which final checks can reveal an incorrect structure.

A student insists that every Lewis structure must give every atom exactly an octet and proposes changing the electron count to make PCl5 and SF6 fit that rule. Explain why this method is unsound and what principle should guide the student's choice of structure instead.

Describe a reliable sequence for drawing a Lewis structure of a polyatomic ion. Include how charge affects the electron count and what must be checked before accepting the structure.

Starting from the O–C–O skeleton, explain how electron counting leads to the accepted Lewis structure for CO₂. Account for the electrons used at each stage and state the final shell and formal-charge checks.

For the Lewis structure O=C=O, calculate the formal charge on each kind of atom using the formal-charge formula, and verify that the total matches the charge of the molecule.

When several plausible Lewis structures are available, explain the main criteria for comparing them. Also clarify what formal charge represents and what it does not represent.

Classify the octet-rule exceptions illustrated by hydrogen, BF₃, BeH₂, NO, PCl₅, and SF₆. State what makes each category an exception and explain why one should not force every example into an octet.

A student says the Lewis structures of BF₃ and BeH₂ must be wrong because their central atoms do not have octets, and proposes changing the electron count to fix them. Evaluate the claim using the specific electron counts around boron and beryllium.

Use valence-electron counting to explain why NO is an odd-electron species and why that affects the possibility of pairing all its electrons.

A learner attempts to reject every Lewis structure with more than eight electrons around a central atom. Use PCl₅ and SF₆ to explain why that rule is too absolute and what should guide the structure instead.

Before drawing nitrite, NO₂⁻, determine its available valence-electron total. Show the contributions from nitrogen, oxygen, and the ionic charge, and state what overall charge the finished Lewis structure must show.

In the nitrite contributor [O=N–O]⁻, nitrogen has one lone pair, the double-bonded oxygen has two lone pairs, and the single-bonded oxygen has three lone pairs. Calculate the formal charge on nitrogen and on each oxygen using formal charge = valence electrons − lone-pair electrons − number of bonds. Verify that the charges sum to the ion's overall charge.

Explain what the two equivalent Lewis contributors for nitrite tell you about its actual structure. In your answer, address whether the ion switches between contributors and what the contributors imply about the two N–O bonds.

A proposed alternative Lewis contributor for NO₂⁻ keeps the nitrogen and oxygen atoms in the same positions but contains 20 electrons and has overall charge 0. Decide whether it can be a resonance form of nitrite, and justify your conclusion using the rules for constructing resonance forms.

Construct a Lewis structure for $\mathrm{CO_2}$ using the standard drawing procedure. Show how the valence-electron count and shell check lead from the initial skeleton to the final bonding arrangement, and state the resulting formal charges.

A proposed three-atom Lewis structure has a central nitrogen with one lone pair and single bonds to two oxygens. Each oxygen has three lone pairs and one bond. Using the formal-charge equation, calculate the formal charge on each atom and infer the structure's overall charge.

Classify each species as an incomplete-octet example, an odd-electron species, or a familiar Lewis representation with more than eight electrons around its central atom: $\mathrm{BF_3}$, $\mathrm{BeH_2}$, $\mathrm{NO}$, and $\mathrm{PCl_5}$. Explain how these classifications affect the use of the octet rule when drawing their structures.

Three proposed Lewis structures use the same atoms, total electron count, and overall charge. Candidate A gives every second-period atom an octet, has small formal-charge magnitudes, and places negative formal charge on the more electronegative atom. Candidate B gives every second-period atom an octet but has larger formal-charge magnitudes and places negative formal charge on the less electronegative atom. Candidate C has smaller formal-charge magnitudes than B but leaves a second-period atom without an octet. Which candidate should be favored, and why are the other two less favorable?

A chemist proposes two pairs of Lewis structures for the same species. In proposal A, the atom positions stay fixed; a lone pair is rearranged to form a π bond, and the total electron count and overall charge remain the same. In proposal B, the total electron count and overall charge remain the same, but one atom changes position in the skeleton. Which proposal describes resonance forms? Explain your decision using the defining constraints on resonance contributors.