Resonance

Related Examples and Practice Problems

Screenshot of a chemistry worksheet titled 'Assignment 3: Lewis and Resonance Structures' with questions about drawing Lewis structures and calculating formal charges for various chemical formulas.
A chemistry worksheet titled 'Resonance Structures Practice' with instructions to draw all possible resonance structures for given ions or molecules, including nitrate ion, formate ion, and cyclobutadiene.
Page from a chemistry textbook illustrating Lewis dot structures and resonance structures of molecule and ions, with diagrams of bonds, electron pairs, and formal charges.

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.

Key Takeaways

  • Resonance occurs when multiple valid Lewis structures exist for the same molecule

  • Real structure is hybrid - average of all resonance forms, not switching between them

  • Atoms don't move - only electron arrangements differ between structures

  • Increases stability - resonance hybrids are more stable than individual structures

  • Creates equivalent bonds - resonance-equivalent positions have identical properties

  • Pattern recognition - look for moveable electrons and equivalent bonding sites

Topic Related Resources

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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.

Video Resources

Blackboard with handwritten notes on Lewis Dot Structures, including diagrams of atomic and molecular structures and calculations related to electrons and atoms.