AP Chemistry Unit 2 Review: Compound Structure and Properties

Instructor Introduction

• Instructor: Jeremy Krug
• Resources: Free review materials available at UltimateReviewPacket.com (unit summary video, practice questions, study guide)

Types of Chemical Bonds

• Ionic Bonds: Between metal and nonmetal
  • Characteristics: Brittle, high melting points, conductive in solution
• Covalent Bonds: Between two nonmetals
  • Characteristics: Lower melting points, poor conductivity
• Subtypes of Covalent Bonds:
  • Polar Covalent: Unequal sharing of electrons, determined by electronegativity difference
  • Nonpolar Covalent: Equal or nearly equal sharing of electrons

Electronegativity and Bond Polarity

• Determine polarity using the periodic table (proximity of atoms)
• Examples:
  • Selenium and iodine: Close, nonpolar
  • Selenium and oxygen: Far, polar

Bond Energy and Length

• Potential Energy: Decreases as atoms bond
• Bond Length: Lowest point on potential energy graph
• Bond Energy: Absolute value at bond length

Bond Order

• Single Bond (1st order): Weakest, longest
• Double Bond: Intermediate strength and length
• Triple Bond (3rd order): Strongest, shortest

Coulomb’s Law

• Variables: Charge and distance
• Charge: Greater charge = stronger attraction
  • Example: Magnesium and sulfide (stronger than chloride)
• Distance: Larger ions = weaker attraction
  • Example: Magnesium and oxide (stronger than sulfide)

Ionic Compounds and Crystal Lattices

• Example: Sodium chloride
• Structure: Repeating 3D lattice, small positive ions, larger negative ions

Metallic Bonding and Alloys

• Metallic Bonding: Delocalized electrons, good conductivity
• Alloys:
  • Substitutional: Atoms substitute positions (e.g., brass)
  • Interstitial: Smaller atoms fit in spaces (e.g., steel)

Lewis Electron-Dot Diagrams

• Drawing Strategy: Start from outside to inside
• Octet Rule: Most atoms stable with 8 valence electrons
• Expanded Octet: Central atom can have more than 8 (e.g., xenon tetrafluoride)
• Resonance Structures: Multiple valid structures (e.g., ozone)

Formal Charge Calculation

• Formula: Valence electrons – assigned electrons
• Example: Oxygen in ozone

VSEPR Theory and Hybridization

• Sigma and Pi Bonds:
  • Single Bond: One sigma
  • Double Bond: One sigma, one pi
  • Triple Bond: One sigma, two pi
• Hybridization: Determined by atoms and electron pairs
  • sp, sp2, sp3: Based on total count

Molecular Geometries and Bond Angles

• Tetrahedral Shape: Bond angle 109.5°
• Common Angles: 109.5°, 120°, 90°, 180°

Conclusion

• Next Steps: Check out Unit 3 review
• Additional Resources: AP-style practice and review at UltimateReviewPacket.com