AP Chemistry Flashcards: Resonance And Formal Charge

What this deck covers

This deck focuses on Resonance And Formal Charge, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Why is resonance important in chemistry?

Answer: Resonance explains stability and properties of molecules. It predicts molecular behavior and chemical properties accurately.

Flashcard 2: How do you determine the major resonance contributor?

Answer: The structure with the lowest formal charges is the major contributor. Lower formal charges indicate greater stability and contribution.

Flashcard 3: Why might a molecule with resonance be less reactive?

Answer: Stability from delocalized electrons reduces reactivity. Electron delocalization creates kinetic stability against reactions.

Flashcard 4: What is the significance of resonance in organic chemistry?

Answer: It explains stability and reactivity patterns of organic molecules. It governs aromaticity, conjugation, and reaction mechanisms.

Flashcard 5: How do resonance structures affect the electron density of a molecule?

Answer: They distribute electron density over multiple atoms. Delocalization spreads charge across multiple atomic centers.

Flashcard 6: Identify the resonance structure with the greatest significance.

Answer: Structure with formal charges closest to zero. Zero formal charges indicate maximum stability contribution.

Flashcard 7: What is the most common mistake when drawing resonance structures?

Answer: Altering the position of atoms. Only electrons move, never nuclear positions.

Flashcard 8: Which resonance structure is preferred: one with charge separation or without?

Answer: Without charge separation. Charge separation increases energy and decreases stability.

Flashcard 9: What is the impact of resonance on molecular geometry?

Answer: Resonance does not change geometry; it affects electron distribution. Electron positions change while atomic positions remain fixed.

Flashcard 10: What is formal charge?

Answer: Formal charge is the charge assigned to an atom in a molecule. It assumes electrons are equally shared in bonds.

Flashcard 11: What role do pi bonds play in resonance?

Answer: Pi bonds allow for electron delocalization. $\pi$ electrons can move to create multiple bonding patterns.

Flashcard 12: How can resonance be identified in a molecule?

Answer: Look for multiple valid Lewis structures. Multiple valid Lewis structures indicate electron delocalization.

Flashcard 13: Why can some molecules not have resonance structures?

Answer: They lack delocalizable electrons. Single bonds prevent electron movement between positions.

Flashcard 14: Identify the formal charge of the sulfur atom in H₂SO₄.

Answer: Formal charge = 0. S has 6 valence, 0 lone pairs, 12 bonding electrons.

Flashcard 15: In nitrate ion (NO₃⁻), what is the formal charge on nitrogen?

Answer: Formal charge = +1. N has 5 valence, 0 lone pairs, 8 bonding electrons.

Flashcard 16: Calculate the formal charge of oxygen in ozone (O₃).

Answer: Central O: +1, Terminal O's: -1 each. Central O forms two bonds; terminal O's form one bond each.

Flashcard 17: Find the formal charge of sulfur in SO₄²⁻.

Answer: Formal charge = 0. S has 6 valence, 0 lone pairs, 12 bonding electrons.

Flashcard 18: What is the purpose of resonance structures?

Answer: Resonance structures represent electron delocalization for stability. They show how electrons spread out to minimize energy.

Flashcard 19: Why is it important to consider formal charge when drawing resonance structures?

Answer: To determine the most stable structure. It identifies which structures contribute most to stability.

Flashcard 20: What does a double-headed arrow indicate in resonance structures?

Answer: It indicates the presence of resonance between structures. Shows electron movement between equivalent Lewis structures.

Flashcard 21: Identify the resonance structure with the lowest energy.

Answer: The structure with formal charges closest to zero. Minimal formal charges indicate maximum stability.

Flashcard 22: How does resonance affect molecular stability?

Answer: Resonance increases molecular stability by electron delocalization. Spreading electrons over more atoms lowers overall energy.

Flashcard 23: Calculate the formal charge of carbon in CH₃⁻.

Answer: Formal charge = -1. C has 4 valence, 2 lone pairs, 6 bonding electrons.

Flashcard 24: Identify the more stable resonance structure: one with full octets or one with formal charges?

Answer: One with full octets. Complete octets provide greater stability than charge separation.

Flashcard 25: What is resonance in chemistry?

Answer: Resonance is the delocalization of electrons across multiple structures. It occurs when electrons can move between multiple valid structures.

Flashcard 26: State the formula for calculating formal charge.

Answer: Formal charge = (valence e⁻) - (nonbonding e⁻) - $\frac{1}{2}$(bonding e⁻). Valence electrons minus lone pairs minus half of bonding electrons.

Flashcard 27: Determine the formal charge on each atom in NH₃.

Answer: N: 0, Each H: 0. All atoms achieve optimal formal charges of zero.

Flashcard 28: What is the key difference between resonance and isomers?

Answer: Resonance involves electron delocalization; isomers differ in connectivity. Resonance keeps connectivity; isomers change atomic arrangement.

Flashcard 29: Which atom often carries a negative formal charge in resonance structures?

Answer: The most electronegative atom. Electronegativity stabilizes negative charge better.

Flashcard 30: Which structure is more stable: one with negative charge on electronegative atom or positive?

Answer: Negative charge on electronegative atom. Electronegativity matches charge distribution for stability.