Physical Science

• IMFA


  Intermolecular forces
• Liquids


  • Resist compression like solids
  • Have the ability to flow like gases
• Surface tension


  The tendency of a fluid to acquire the least possible surface area
• Surface tension

  • Water droplet exhibiting surface tension
• Cohesive forces


  Attractive forces that exist between molecules of the same kind
• Adhesive forces


  Attractive forces that exist between the molecules of different types, such as a liquid and a solid surface
• Molecules with stronger intermolecular forces

  Exert greater cohesive forces and acquire less surface area than those with weaker IMFA
• Liquids with strong IMFA

  Have high surface tensions
• Meniscus


  The curved upper surface of a liquid in a container
• Meniscus

  • Concave meniscus
  • Convex meniscus
• Adhesive forces between water and glass surface


  Stronger than cohesive forces between water molecules, resulting in a concave meniscus
• Cohesive forces stronger than adhesive forces

  Results in a convex meniscus, e.g. mercury in a glass container
• Capillary action


  The rise of a liquid in a tube with a small diameter due to cohesive and adhesive forces
• Distance the liquid travels up the tube

  Increases with decreasing diameter of the tube
• Viscosity


  The measure of a fluid's resistance to flow
• Molecules with stronger intermolecular forces

  Have greater resistance to flow because it is difficult for the molecules to move and slide past one another
• Temperature increases

  Molecules have more energy and it becomes easier to overcome the IMFA, reducing viscosity
• Vapor pressure


  The pressure exerted by a vapor in equilibrium with its liquid phase in a closed system
• Molecules with stronger intermolecular forces

  Have less tendency to escape as gas, and thus, lower vapor pressure compared to those with weaker IMFA
• Volatility


  The tendency of a liquid to evaporate
• Example of a Volatile liquid

  • Acetone
• Intermolecular forces


  Attractive forces present in between molecules
• Types of intermolecular forces of attraction (IMFA)

  • London dispersion forces
  • Dipole-dipole forces
  • Ion-dipole forces
  • Hydrogen bonding forces
• London dispersion forces (LDFs)

  • Weakest type of IMFA
  • Present in between all electrically neutral molecules (polar and nonpolar)
  • Caused by fluctuations in the electron distribution within atoms or molecules
• London dispersion forces (LDFs)

  1. Temporary dipole induces instantaneous dipoles to neighboring molecules

  2. Molecules can have instantaneous dipoles when electrons move around the nucleus
• Polarizability


  Measure of how easy it is to distort the electron distribution of a molecule
• Bromine (Br2) vs Chlorine (Cl2)

  Br2 has stronger London dispersion forces than Cl2 due to more electrons
• Strength of LDF

  Affects boiling points
• Dipole-dipole forces

  • Moderately strong type of IMFA
  • Present in between polar molecules
• Dipole-dipole forces

  • Attraction between partially positive and partially negative ends of HCl molecules
• Ion-dipole forces

  • Result from the electrostatic attraction of a molecule containing a dipole and an ion
  • Strength increases as the charge of ion increases
  • One of the strongest types of IMFA
• Ion-dipole forces

  Cation attracted to partial negative end, anion attracted to partial positive end
• Hydrogen bonding

  Attractive force that exists when hydrogen is bonded to F, O, or N
• Hydrogen bonding


  • Hydrogen bond formation between water and formaldehyde