Introduction to Organic Chemistry and Lewis Structures

Aug 19, 2024

Organic Chemistry Introduction and Lewis Structures

Course Overview

  • Focus: Organic Chemistry basics and review of General Chemistry
  • Format: Whiteboard teaching, weekly lessons
  • Topics:
    • Lewis Structures
    • Formal Charges
    • Hybridization and Valence Bond Theory
    • Molecular Orbital Theory
    • Polarity and Intermolecular Forces

Introduction to Organic Chemistry

  • Organic vs Inorganic Chemistry:
    • Organic: Study of carbon-containing compounds
    • Inorganic: Study of non-carbon elements
  • Carbon Importance: Focus on carbon, less on transition metals
  • Teaching Variability:
    • Different textbooks/professors may teach differently
    • Emphasis on understanding variability and trends

Lewis Structures

  • Valence Electrons: Determined by periodic table group
    • Group 1: 1 electron
    • Group 2: 2 electrons
    • Group 13: 3 electrons
    • Group 14 (Carbon): 4 electrons
    • Group 15: 5 electrons
    • Group 16 (Oxygen): 6 electrons
    • Group 17 (Halogens): 7 electrons
    • Group 18 (Noble Gases): 8 electrons (no bonding)

Octet Rule

  • Basic Concept: Atoms aim for 8 valence electrons
  • Shell and Subshells:
    • S subshell: 2 electrons
    • P subshell: 6 electrons
    • Total: 8 electrons for an octet
  • Exceptions:
    • Expanded Octet: Elements in 3rd period and below can exceed 8 electrons (example: Sulfur)
    • Below Octet: Hydrogen (2 electrons), Beryllium (4 electrons), Boron and Aluminum (6 electrons)
    • Odd Electrons: Rare in organic chemistry (e.g., NO)

Lewis Structure Construction

  1. Count Valence Electrons
  2. Determine Central Atom (least electronegative, not hydrogen)
  3. Create Skeleton Structure with single bonds
  4. Fill Outer Atoms first
  5. Account for Electrons
  6. Check if Central Atom is Happy (has an octet)

Example Structures

  • CH₄ (Methane): Carbon central, forms four bonds with hydrogen
  • NH₃ (Ammonia): Nitrogen central, forms three bonds, one lone pair
  • H₂CO (Formaldehyde): Carbon central, double bond with oxygen
  • CH₃CHO (Acetaldehyde): Carbon double-bonded to oxygen
  • CH₃COOH (Acetic Acid): Carboxylic structure, central carbon bonded to two oxygens

Conclusion

  • Practice Recommended: Reinforce through study guides and exercises
  • Further Study: Formal charge and molecular geometry in future lessons

Note: By end of Chapter 2, recognition of condensed formulas and typical structures is crucial.