AP Chemistry Unit 3 Review: Properties of Substances and Mixtures

Introduction

• Presented by Jeremy Krug
• Video covers key concepts of AP Chemistry Unit 3
• Full review with guided notes and questions available at Ultimate Review Packet dot com

Intermolecular Forces

• London Dispersion Forces
  • Present in all molecules, weakest type
  • Stronger in larger molecules due to more electrons
  • Only force in nonpolar molecules
• Dipole-Dipole Forces
  • Present in polar molecules
  • Positive pole attracts negative pole of neighbors
  • Typically stronger than dispersion forces
• Hydrogen Bonding
  • Occurs in molecules with H bonded to O, F, or N
  • Strongest type of intermolecular force
• Ion-Dipole Forces
  • Occur between polar molecules and ions
  • Important in dissolving ionic compounds

Solids

• Ionic Solids
  • High melting points, brittle, conduct electricity when dissolved
• Covalent Network Solids
  • Very strong, bonded in multiple directions (e.g., diamond, silicon dioxide)
• Molecular Solids
  • Weak forces, low melting points (e.g., sugar)
• Metallic Solids
  • Malleable, ductile, conduct electricity, surrounded by sea of electrons
• Amorphous Solids
  • Non-crystalline (e.g., plastics)

States of Matter

• Solid: Particles close, vibrational motion only
• Liquid: Particles further apart, can flow
• Gas: Particles far apart, independent movement, compressible

Ideal Gas Law

• Formula: PV=nRT
  • Pressure (P) in atmospheres, Volume (V) in liters
  • n = moles of gas, T = temperature in Kelvin
  • R = 0.08206 L atm/mol K (Universal Gas Constant)

Gas Mixtures

• Total pressure = sum of partial pressures
• Partial pressure determined by mole fraction and total pressure

Temperature and Kinetic Energy

• Temperature = average kinetic energy
• Boltzmann distribution shows range of motion

Ideal Gases

• No intermolecular attractions, no space taken up by particles
• Best approximated at high temperatures and low pressures

Mixtures

• Heterogeneous: Components visible
• Homogeneous: Uniform distribution (solutions)
• Molarity: Moles of solute/liters of solution

Separation Techniques

• Distillation: Based on boiling points
• Chromatography: Based on adhesion to stationary phase

Solubility

• "Like dissolves like": Polar with polar, nonpolar with nonpolar

Electromagnetic Spectrum

• UV/visible light: Electron transitions
• Infrared: Molecular vibrations
• Microwave: Molecular rotations

Light and Photons

• Dual nature: Wave and photons
• Equations:
  • c = λν (Speed of light = wavelength x frequency)
  • E = hν (Energy = Planck's constant x frequency)

Spectrophotometry

• Beer-Lambert Law: A = εbc
  • A = absorbance, ε = molar absorptivity, b = path length, c = concentration
  • Calibration curve for unknown concentrations