Lewis Structures, Resonance & Bond Models — Practice · Grade 11 Science
Chapter: Bonding, Formulas & Molecular StructureWhat this practice covers
By the end of Lewis Structures, Resonance & Bond Models you should be able to:
- I can count valence electrons and check a Lewis structure’s total charge.
- I can distinguish resonance, electron-domain geometry, and molecular shape.
8 questions, numeric and written answer, each with a worked explanation.
Vocabulary used: lone pair, formal charge, resonance.
Problem 1
Hints
Write the relationship first; substitute with consistent units.
Answer and explanation
8 electrons
5+4−1 = 8.
Problem 2
Answer and explanation
Its electron density points in one bond direction, despite containing two shared pairs.
Response criteria
- State a scientifically accurate conclusion.
- Show the calculation or mechanism that supports it.
- Include units, conditions, or limits where relevant.
Problem 3
Hints
List the given quantities, select a relationship, and check units before substituting.
Answer and explanation
32 electrons
6+4×6+2=32.
Problem 4
Answer and explanation
No. Resonance drawings represent one delocalized bonding structure with equivalent bonds in the idealized ion.
Response criteria
- State a scientifically accurate conclusion.
- Show the calculation or mechanism that supports it.
- Include units, conditions, or limits where relevant.
Problem 5
Hints
Formal electron counting is a model; resonance is not rapid physical switching.
Answer and explanation
5 from N plus 3 from H=8; three bonds and one lone pair on N in the simple model.
Problem 6
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
They help evaluate plausible electron arrangements, with known exceptions and charge constraints.
Problem 7
Answer and explanation
The electron inventory represents a species with one fewer electron than the neutral-atom sum; the assignments must reproduce that total charge.
Formal charge assigns bonding electrons equally between bonded atoms: valence count minus nonbonding electrons minus half the bonding electrons. In NH₄⁺, nitrogen has four single bonds and no lone pair, giving formal charge +1; each hydrogen has zero. The sum must equal the species’ net charge. Formal charge helps compare Lewis candidates but is not a direct measurement of actual partial charge, and it is distinct from oxidation-number bookkeeping, which assigns bonding electrons differently.
The electron inventory represents a species with one fewer electron than the neutral-atom sum; the assignments must reproduce that total charge.
Response criteria
- Interpret labels, structures, axes, units and directions correctly.
- Explain the chemistry relationship or mechanism.
- Respect stated assumptions and distinguish observation from inference.
Problem 8
Answer and explanation
Total valence electrons are 5+4(1)−1=8. Nitrogen formal charge is 5−0−4=+1 and each H is zero. The flat Lewis connectivity does not specify measured angles; the common molecular arrangement is tetrahedral.
Total valence electrons are 5+4(1)−1=8. Nitrogen formal charge is 5−0−4=+1 and each H is zero. The flat Lewis connectivity does not specify measured angles; the common molecular arrangement is tetrahedral.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the chemical mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.