U5 - Intermolecular Forces and Properties

• Intermolecular Forces (IMFs) - The forces that hold one molecule to another

  In order of strongest to weakest force:

  1. Macro-Covalent
  2. Macro-Ionic
  3. Metallic
  4. Hydrogen Bonding
  5. Dipole-Dipole
  6. London Dispersion
• The stronger the intermolecular forces, the higher the boiling point.
• Macro-Covalent - Large structures held together by a network of colvalent bonds

  
  

  Strongest of all IMFs

  
  

  State of Matter at Room Temperature: Solid
• Macro-Covalent examples

  • Diamonds
  • Rocks
  • All carbon atoms
  • Silicon and oxygen atoms
• Macro-Ionic - Large crystalline structures held together by a network of ionic bonds.

  
  

  State of Matter at Room Temperature: Solid
• Macro-Ionic examples

  • NaCl: table salt
  • CuSO4
  • Any ionic bonded molecule, including transition metals
• Metallic - Force formed by metal atoms that disassociate their electrons into a "sea of electrons". This creates many dipoles through the atom, they shift but are always there.

  State of Matter at Room Temperature: Solid
• Metallic Examples

  • Copper
  • Iron
  • Alloys (Brass, bronze, steel)
• Alloys can be used to strengthen and make metals lighter.
• Dipole-Dipole - Attractive forces between polar covalent molecules. Caused by the attraction of a positive end of one polar molecule to a negative end of another polar molecule.

  State of Matter at Room Temperature: Liquid
• Dipole-Dipole examples

  • Iodine Monochloride (ICI)
  • Hydrosulfuric Acid (H2S)
• Hydrogen Bonding - A stronger type of dipole-dipole force. Dipole-Dipole attractions of molecules with Nitrogen-Hydrogen, Oxygen-Hydrogen, and Fluorine-Hydrogen chemical bonds. The more hydrogen bonding sites in a molecule, the stronger the intermolecular force is. NOT A CHEMICAL BOND

  State of Matter at Room Temperature: Liquid

  * The reason the attractions in hydrogen bonding are only nitrogen, oxygen, and fluorine is because they are the three most electronegative elements.
• Hydrogen Bonding Examples

  • H2O
  • NH3
  • HF
• London Dispersion - Attractive force between non-polar covalent molecules. A momentary dipole is generated as electrons move around atoms. The weakest intermolecular force.

  State of Matter at Room Temperature: Gas
• London Dispersion Examples

  • Noble Gases
  • Diatomic Molecules; i.e. H2, and F2
• Dipole induced Dipole - weak attractions when a polar molecule induces a dipole in a non-polar molecule by disturbing the arrangement of electrons in the non-polar molecule.