Resonance

Related Examples and Practice Problems

Additional Worked Out Examples/ Practice

  • Identifying classification types: Differentiation between elements, compounds or mixtures and homogeneous and heterogenous mixtures

  • Separation techniques: Selected and explaining limitation of appropriate separation

  • Relating Properties to Composition: Predicting classification based on descriptive properties

Topic Summary & Highlights
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Core Concept

Resonance refers to a situation where more than one valid Lewis structure can be drawn for a molecule. These structures are called resonance structures and differ only in the arrangement of electrons, not in the arrangement of atoms.

Purpose of Resonance: It reflects the delocalization of electrons in molecules where bonding can't be described by a single Lewis structure.

Practice Tips

  • Memorize Common Ions: Focus on learning the common polyatomic ions, charges, and patterns.

  • Molecules with extensive resonance (e.g., benzene) are more stable due to delocalized electrons.

  • Not all resonance forms contribute equally; more stable structures (e.g., lower formal charges) dominate the resonance hybrid.

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Core Concept

What are Resonance Structures?

  • Key Concept: A resonance structure is a way to represent bonding in a molecule where electron pairs are distributed across multiple positions. It is a tool to depict the delocalization of π-electrons or lone pairs.

  • Note: No single resonance structure fully describes the molecule; the actual structure is a hybrid, often called the resonance hybrid, that averages the contributions from each resonance structure.

Examples of Resonance Structures

  • Ozone (O₃)

  • Benzene (C₆H₆)

  • Carbonate Ion (CO₃²⁻)

Rules for Drawing Resonance Structures

  • Rule 1: The positions of the atoms must remain the same in all resonance structures.

  • Rule 2: Only the arrangement of electrons (usually π-electrons or lone pairs) changes.

  • Rule 3: Each resonance structure must follow the normal rules of bonding (octet rule, formal charges, etc.).

  • Rule 4: The resonance hybrid is more stable than any individual resonance structure and represents the actual electron distribution.

Delocalization of Electrons and Resonance Stability

  • Electron Delocalization: In resonance structures, electrons are shared or spread over multiple atoms, which provides stability to the molecule.

  • Resonance Hybrid: The actual molecule is a blend or hybrid of all resonance structures, resulting in greater stability due to delocalized electrons.

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