Intermolecular forces

• types of intermolecular forces 


  • permanent dipole - permanent dipole/permanent induced dipole
  • hydrogen bonds
  • induced dipole - induced dipole/London forces
• • permanent dipole-dipole interactions act between the permanent dipoles in different polar molecules.
  • the electron density is permanently closer to the more electronegative atom.

  
• hydrogen bonds are a special type of PD-PD interactions, what molecules do they exist between?


  they feisty between a molecule with a hydrogen directly bonded to a F N O atom
• what do London forces occur between?


  non polar molecules
• order the strength of IMF forces

  1. hydrogen bonds
  2. permanent dipole dipole interactions
  3. London forces
• What type of bonding do all simple molecules have?

  Covalent bonding
• Why do simple molecules have low melting and boiling points?

  Because their weak intermolecular forces do not require much energy to break
• What happens to covalent bonds during the melting of a simple molecule?

  The covalent bonds do not break
• What is the solubility behavior of non-polar simple molecular substances in non-polar solvents?

  • Intermolecular forces form between the simple molecular compound and the non-polar solvent.
  • These interactions weaken the intermolecular forces in the simple molecular lattice.
  • The forces break, allowing the compound to dissolve.
  • Therefore, non-polar simple molecular substances tend to be soluble in non-polar solvents.
• What occurs when a simple molecular substance is added to a polar solvent?

  There are very few interactions between the molecules in the lattice and the solvent molecules
• Why do simple molecular substances tend to be insoluble in polar solvents?

  Because the intermolecular bonding within the polar solvent is too strong to be broken
• What are the key characteristics of simple molecular substances regarding their bonding and solubility?

  • Covalently bonded with weak intermolecular forces
  • Low melting and boiling points
  • Insoluble in polar solvents
  • Soluble in non-polar solvents