AP Chem Unit 3

• What are intermolecular forces?

  Forces that make molecules stick together
• How do intermolecular forces differ from intramolecular forces?

  Intermolecular forces are between molecules, while intramolecular forces are within a molecule
• What types of bonding are primarily associated with intramolecular forces?

  Covalent and ionic bonding
• What physical properties are affected by intermolecular forces?

  Boiling point, melting point, surface tension, and vapor pressure
• How do intramolecular forces affect a substance?

  They affect how reactive or unreactive the substance is
• Which type of forces are generally weaker: intermolecular forces or covalent/ionic bonds?

  Intermolecular forces
• What are London dispersion forces?

  A fundamental type of intermolecular force that occurs due to temporary dipoles
• What is another name for London dispersion forces?

  Dispersion forces
• How does the electron distribution in an atom lead to an instantaneous dipole?

  Electrons move and can create a temporary uneven distribution
• What happens when an instantaneous dipole affects a nearby atom?

  It induces a dipole in the nearby atom
• What is the difference between an instantaneous dipole and an induced dipole?

  An instantaneous dipole occurs due to random electron movement, while an induced dipole is caused by the influence of a nearby dipole
• Why do all molecules exhibit London dispersion forces?

  Because all molecules can have instantaneous dipoles
• How does the number of electrons in a molecule affect its London dispersion forces?

  More electrons lead to stronger London dispersion forces due to increased polarizability
• What is the relationship between intermolecular forces and boiling/melting points?

  Stronger intermolecular forces result in higher boiling and melting points
• What type of molecules typically have the strongest London dispersion forces?

  Large nonpolar molecules
• Why do some polymers have stronger intermolecular forces than polar molecules?

  Because they have many electrons due to their large size
• Which molecule has a higher boiling point: butane or methane? Butane ➡️ C4H10 Methane ➡️ CH4

  Butane
• How can you determine which nonpolar molecule has stronger London dispersion forces?

  By comparing the number of electrons in the molecules
• How do you rank nonpolar molecules in order of increasing boiling point?

  • Consider polarizability: more polarizable = higher boiling point
  • Fewer electrons = lower boiling point
  • Example ranking: Helium < Argon < Propane
• How can you predict relative boiling points of nonpolar molecules?

  By looking at the number of electrons they have
• What is the significance of London dispersion forces in chemistry?

  • Present in all molecules
  • Affect physical properties like boiling and melting points
  • Important for understanding nonpolar molecules
• What is vapor pressure?

  The pressure exerted by a vapor back down on the liquid from which it evaporated
• How does temperature affect vapor pressure?

  As temperature increases, the vapor pressure of a liquid increases
• What happens to vapor pressure when intermolecular forces are weak?

  Weaker intermolecular forces correlate to higher vapor pressures
• What is the relationship between intermolecular forces and boiling point?

  Weaker intermolecular forces result in lower boiling points
• How does vapor pressure relate to boiling point in liquids?

  • Weaker intermolecular forces lead to higher vapor pressure
  • Higher vapor pressure means lower boiling point
  • Stronger intermolecular forces lead to lower vapor pressure
  • Lower vapor pressure means higher boiling point
• What does the x-axis of the vapor pressure graph represent?


  The temperature in degrees Celsius
• What does the y-axis of the vapor pressure graph represent?

  The vapor pressure in kilopascals
• How does elevation affect the boiling point of water?

  Higher elevation results in lower boiling points due to decreased pressure
• Which liquid has the weakest intermolecular forces based on vapor pressure?

  Propanone has the weakest intermolecular forces
• What are ionic solids composed of?

  Ionic compounds arranged in a crystal lattice
• Why are ionic compounds like salt brittle?

  They shatter when the crystal lattice is disturbed
• How do ionic solids conduct electricity?

  They conduct electricity when dissolved in water or melted
• What are molecular solids composed of?

  Covalently bonded compounds
• Why do molecular solids have low boiling points?

  The forces holding molecules together are relatively weak
• What is an example of a covalent network solid?

  Diamond
• Why is diamond considered one of the hardest materials?

  It has a strong repeating network of covalent bonds
• How does silicon dioxide compare to carbon dioxide in terms of boiling point?

  Silicon dioxide has a higher boiling point than carbon dioxide
• What are the types of solids discussed in the material?

  • Ionic solids: Composed of ionic compounds in a crystal lattice
  • Molecular solids: Composed of covalently bonded compounds
  • Covalent network solids: Strong structures with repeating covalent bonds
• What type of forces hold carbon dioxide molecules together?

  London dispersion forces