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Understanding Electrons and Chemical Bonds

Apr 23, 2025

Lecture Notes: Electrons and Chemical Bonding

Overview

  • Focus on electrons, their roles in chemistry.
  • Importance of understanding foundational concepts from Unit 1 for Units 2 and 3.

Electrons

  • Electron Cloud: Area surrounding the nucleus where electrons are found.
  • Charge: Electrons have a negative charge.

Types of Electrons

  1. Core Electrons
    • Close to the nucleus, low energy.
    • Do not participate in chemical reactions.
  2. Valence Electrons
    • Higher energy, found in outer s and p sub shells.
    • Participate actively in chemical bonding.

Valence Electrons in Elements

  • Periodic Table Insight: Elements in the same group have the same number of valence electrons.
  • Examples:
    • Chlorine: 7 valence electrons (5 in 3p, 2 in 3s).
    • Fluorine and Bromine: Both have 7 valence electrons.
  • Group Number Correlation: Group number equals number of valence electrons.

Octet Rule

  • Goal: Atoms aim to have a filled outer shell (8 valence electrons for s and p shells).
  • Exceptions:
    • Hydrogen and Helium target a "duet" (2 electrons) due to their electron configuration.

Chemical Bonds

  1. Ionic Bonds
    • Formed from attraction between oppositely charged ions.
  2. Covalent Bonds
    • Result from sharing electrons between atoms.
  3. Metallic Bonds
    • Network of electrons between metal atoms.

Ionic Bonding and the Octet Rule

  • Example with Sodium and Chlorine:
    • Sodium loses 1 electron to become Na⁺.
    • Chlorine gains 1 electron to become Cl⁻.
    • Result: Formation of NaCl (table salt).

Determining Chemical Formulas

  • Use oxidation states to predict the combination of elements:
    • Calcium and Phosphorus: Ca₃P₂.
    • Potassium and Phosphorus: K₃P.
  • Crisscross Method: Use charges to determine subscripts in formulas.
  • Reduction: Simplify formulas if possible (e.g., CaO instead of Ca₂O₂).

Polyatomic Ions

  • Definition: Groups of atoms that net a charge.
  • Examples:
    • Ammonium (NH₄⁺)
    • Phosphate (PO₄³⁻)
  • Formula Examples:
    • Potassium and Phosphate: K₃PO₄.
    • Calcium and Phosphate: Ca₃(PO₄)₂.
    • Ammonium and Sulfate: (NH₄)₂SO₄.

Additional Notes

  • Review notes and homework for more practice.
  • The professor is available for questions and office visits.
  • Upcoming: Discussion on exam results and further exploration of ionic bonding.

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