Chem

• Intramolecular forces


  Forces "WITHIN" molecules, bonding forces
• Intermolecular forces

  Forces "BETWEEN" molecules
• How do IMFs relate to the state of matter?

  IMFs hold the particles of liquid and solid close together, only when thermal energy (heat) is high enough, does it overcome (liquid—gases)
• Properties of the state of matter

  • Gas: Low density, Indefinite shape, Indefinite volume, Weak strength
  • Liquid: High density, Indefinite shape, Definite volume, Moderate strength
  • Solid: High density, Definite shape, Definite volume, Strong strength
• Strength of IMFs

  Strong IMFs - solid or liquid, Weak IMFs - gas
• Determining strength of IMFs

  Boiling Point - for liquid, Melting Point - for solid
• Types of Intermolecular Forces

  • Dispersion (London) Forces
  • Dipole-Dipole Forces
  • Hydrogen Bonding
  • Ion-dipole
• Dispersion (London) Forces


  Exists in all molecules and atoms, Instantaneous Dipole - Induced Dipole = Dispersion Force (very weak attractive force), Increase with molar mass
• Dipole-Dipole Forces


  Exists in all polar molecules, Molecules with permanent dipoles (electron rich and electron poor regions) align positive and negative regions, The Stronger the Dipole (stronger IMF), The Higher the BP
• Hydrogen Bonding


  Strongest IMF in a pure substance
• Ion-dipole


  Present in mixture of ionic and polar compounds
• Other Manifestations of IMFs

  • Surface Tension (shrinking)
  • Viscosity (resistance to change in shape)
  • Capillary Action (ascension of liquids)
• Surface Tension


  Tendency of liquids to minimize their surface area, Energy required to increase the surface area by some unit amount, Directly related to strength of IMFs
• Viscosity


  Resistance of a liquid to flow, Increases with molar mass and length, Decreases with temperature
• Capillary Action


  Liquid rising in a tube, Combination of Cohesive (attraction between molecules in liquid) and Adhesive (attraction between molecules and surface of the tube) forces
• Solution


  A homogeneous mixture composed of two or more substances
• Electrolytes


  Substances that become ions in solution and acquire the capacity to conduct electricity
• Non-electrolyte


  Substance that does not dissociate into ions and so in solution it is a nonconductor of electricity
• Colligative Properties


  Physical properties of a solvent which depend upon the amount of solute present in a solution
• Lowering the Vapor Pressure


  Non-volatile solvents reduce the ability of the surface solvent to escape the liquid, Temperature sensitive, The amount of vapor pressure lowering depends on the amount of solute
• Boiling-Point Elevation


  Temperature at which Vapor Pressure = External Atmospheric Pressure, Non-volatile solute lowers the vapor pressure, Therefore, the triple point-critical point curve is lowered
• Freezing Point Depression


  The solution freezes at a lower temperature than the pure solvent, When a solution freezes, almost pure solvent is formed first
• Osmosis


  Movement of a solvent from an area of high solvent concentration to an area of low concentration across a semipermeable membrane, Osmotic pressure, π, is the pressure required to stop osmosis, πV = nRT, π = (n/V) RT = MRT
• Determination of Molar Mass

  Usually use freezing point depression or boiling point elevation, Calculate Molality or Molarity, Need to be given mass of solute, Calculate molar mass
• Energy of Solution Formation

  To form a solution, must have the same Polarity, The formation of liquid solution takes place in 3 steps: 1) Overcoming the intermolecular forces in the solvent to give room for the solute, 2) Separating the solute into its individual components, 3) Allowing the solute and solvent to interact to form the solution
• Enthalpy of Solution

  The enthalpy change associated with the formation of the solution, Equal to the sum of the ΔH values for the three steps, Positive enthalpy - endothermic process, Negative enthalpy - exothermic process
• Types of Concentration

  • Percent by Mass
  • Percent by Volume
  • Percent by Mass-Volume
  • Mole Fraction
  • Molality
  • Molarity
  • Parts per Million