AP Chemistry: Intermolecular Forces and Properties (Unit 3)

Overview

• Focus on intermolecular forces and properties
• Topics include:
  • Hydrogen bonding
  • Dipole-dipole forces
  • London dispersion forces
  • Ideal gas laws and deviations
  • Spectroscopy and Beer's Law

Intermolecular Forces

• Definition: Forces of attraction between molecules
• Types of Intermolecular Forces:
  • London Dispersion Force: Weakest, between non-polar molecules or noble gases, based on temporary dipoles
  • Dipole-Dipole Interaction: Between polar molecules, based on permanent dipoles
  • Hydrogen Bonding: Strongest among dipole interactions, occurs in molecules with N, O, or F bonded to H
  • Ion-Dipole Force: Strongest overall, between ions and polar molecules

London Dispersion Forces

• Occur in nonpolar molecules and noble gases
• Depend on polarizability and contact area
• Larger molecules or those with more electrons have greater London dispersion forces

Dipole-Dipole Interaction

• Occurs in polar molecules with permanent dipoles
• Polar molecules have both dipole-dipole interactions and London dispersion forces

Hydrogen Bonding

• Special dipole-dipole interaction
• Occurs in molecules with hydrogen bonded to N, O, or F
• Examples: Water (H2O), Ammonia (NH3)

Ion-Dipole Forces

• Strongest of the intermolecular forces
• Explain solubility of ionic compounds in water

Covalent Network Structures

• Atoms bonded covalently in a 3D network
• High melting/boiling points due to strong covalent bonds
• Examples: Diamond, Graphite, Silicon Dioxide

States of Matter

• Solids: Fixed shape and volume
• Liquids: Fixed volume, no fixed shape
• Gases: No fixed volume or shape, particles move freely

Ideal Gas Law

• PV = nRT (Pressure x Volume = Moles x Gas constant x Temperature)
• Assumes no intermolecular forces and point-size particles

Real Gases

• Deviate from ideal behavior at high pressures and low temperatures
• Larger molecules exhibit greater deviation

Kinetic Molecular Theory

• Gas particles are in constant, random motion
• Temperature relates to average kinetic energy
• Maxwell-Boltzmann distribution describes speed distribution among particles

Spectroscopy

• Use of electromagnetic radiation to study matter
• Photoelectric effect: Light ejects electrons from metal surfaces
• Beer-Lambert Law relates absorbance to concentration

Chromatography

• Separates substances based on differences in intermolecular forces
• Types: Paper chromatography, column chromatography

Electromagnetic Spectrum

• Includes all types of light (Gamma rays to Radio waves)
• Visible light is a small part of the spectrum
• Wavelength and frequency are inversely related

Photoelectric Effect

• Explains light as particles (photons)
• Photon energy: E = hν (Planck’s constant x Frequency)
• Higher frequency light ejects electrons from metal surfaces

Applications in Chemistry

• Determining solubility and molecular structure
• Analyzing substances through spectrophotometry
• Understanding molecular motion and reactions

These notes provide a comprehensive overview of Unit 3 in AP Chemistry, covering all major concepts related to intermolecular forces, states of matter, gas laws, and applications in spectroscopy.