midterm

• Intermolecular Forces (IMF)


  Attractions between one molecule and a neighboring molecule
• Intermolecular Forces (IMF)


  • Determines whether a solute dissolves in a particular solvent
  • Without it, there could be no molecular solid or liquid
  • Helps gases behave more ideal
  • The stronger the attractions between particles, the more difficult it will be to separate the particles
  • One of the main factors that determine Boiling Point and Melting Point of an organic compound
• Intramolecular Forces


  Force within a molecule
• Van der Waals Forces or London Force


  • Weakest Intermolecular Force
  • Brought about by the fluctuating charge of the molecule
  • Results in a temporary dipole
  • Causing induced polarization
  • All molecules have this force
  • Occurs in neutral, non-polar molecules
  • Increase in no. of C = increase Van der Waals Force
  • Branching - causes a decrease of Van der Waals Force
• Methane


  • No dipole-dipole interaction
  • No hydrogen bonding
  • Only LDF
  • Boiling Point - -164°C
  • At Room Temperature - -20-25°C
  • Gas
• Butane


  • Boiling Point - -1-1°C
• Dipole-Dipole


  • Observed among partly ionic or polar molecules
  • Brought about by the interaction of two charges at both ends
  • One is slightly positive and the other is slightly negative
  • Greater polarity = Stronger dipole-dipole attraction
  • Induces polarization causing a positive charge to be negative
  • Separation of charge
• Acetone


  • Boiling Point - 56°C
  • At Room Temperature - liquid
• Diethyl ether


  • Boiling Point - 35°C
• Hydrogen Bonding


  • Strongest type
  • Can either be intramolecular or intermolecular
  • Intermolecular H-Bonding - raises the boiling point of organic compounds
  • Intramolecular H-Bonding - lowers the boiling point
  • Occur between polar covalent molecules that possess a hydrogen bonded to an extremely electronegative element
• Water


  • Boiling Point - 100°C
  • Takes more energy to pull the water molecules apart
  • At Room Temperature - liquid
• 1. Butanol


  • Boiling Point - 117°C
• • To identify if hydrogen bonding is present, identify where hydrogen is bonded to
  • Has to be bonded to another electronegative atom
  • For there to be a big enough difference in electronegativity
• Boiling Point


  Temperature at which the vapor pressure of the substance equals the pressure of the atmosphere above it
• Boiling Point


  • Physical constant
  • Can be used in identification and characterization, as well as a criterion of purity of substance
  • Theoretical Value - constant boiling point
  • Experimental Value - what we need in the laboratory
  • Lowering - addition of one substance to another
  • Different Boiling Point - due to the intermolecular forces operating between the molecules of the liquid
• Toluene


  • Initial Temperature - starts to boil
  • Final Temperature - constant reading of boiling point
  • Initial temperature + Final temperature / 2 = 111°C
• • Pure Compounds - have a constant boiling point
  • Mixtures - have a boiling point range
  • Except for Azeotropes
  • Compounds involving Ionic Bonds - have higher boiling point
• Factors that affect the Boiling Point


  • Strength of intermolecular forces
  • Length of Carbon-Carbon chain
  • Branching decreases the boiling point
  • Polarity
  • Impurities
• Melting Point


  Temperature at which a solid melts and becomes liquid
• Melting Point


  • Will depend on the structure of the molecule involved
  • Molecular motion due to increase thermal energy
  • Enough to breakdown the lattice structure of the crystal
  • Solid - higher melting point
  • Its molecule absorbs energy in the form of heat
  • Force of Attraction - decreases
  • Molecules become increasingly separated
  • Weak - lower melting point
  • Separation of the molecules increases by a large amount and the solid melts and turns into a liquid
• Naphthalene


  • Initial Temperature - temperature when the naphthalene starts to melt
  • Final Temperature - temperature when the naphthalene is completely melted
  • Add the initial and final temperature / 2 = 80°C
• • Different compounds tend to have different melting points
  • Most Important Application - confirmation of synthesized organic compounds
• Factors that affect the Melting Point


  • Molecular Symmetry
  • Molecular Size
  • Polarity/Intermolecular Forces
  • Impurities
• pH


  • Measures the acidic or basic property of substances
  • Negative logarithm (base 10) of hydrogen ion concentration

  
• Acids


  • Substances that produce free hydrogen ions (H+ ions) when dissolved in water
  • Acidic Solutions - rich in hydrogen ions
  • Weak Acids - dissociate only partly
  • Strong Acids - dissociate completely

  
• Bases


  • Substances that produce hydroxyl ions (OH- ions) when dissolved in water
  • Basic Solutions - poor in hydrogen ions
  • Weak Bases - dissociate partly
  • Strong Bases - dissociate completely

  
• Arrhenius Acids and Bases


  • Acid - H+
  • Base - OH-
• Bronsted-Lowry Acids and Bases


  • Acid - Proton Donor
  • Base - Proton Acceptor
• Lewis Acids and Bases


  • Acid - Proton Acceptor
  • Base - Proton Donor
• pH Scale


  • 0-1 - strong acid
  • 2-4 - moderately acidic
  • 5-6 - weak acid
  • 7 - neutral
  • 8-9 - weak base
  • 10-12 - moderately basic
  • 13-14 - strong base
• NaOH


  • 12 (moderately basic)
• HCl


  • 1 (strong acid)
• Vinegar


  • 3 (moderately acidic)
• Baking Soda

  • 8 (weak base)
• Lemon Juice

  • 3 (moderately acidic)
• Window Cleaner (Ammonia)

  • between 7 and 8 (neutral to weak base)
• Dranal

  • 12 (moderately basic)
• Detergent

  • between 9 and 10 (weak base to moderately basic)
• Sodium bicarbonate

  • 9 (weak base)
• 0.1 M HCl

  • 1 (strong acid)