Forces of Attraction

• Ionic Bond

  • Transfer of electrons
  • Between metals (LEORA) and nonmetal (GEROA)
• Covalent Bond

  • Sharing of electrons
  • Between nonmetals and nonmetals
  • Polar covalent electrons are shared unequally.
  • Nonpolar covalent-electrons are shared equally.
• Hydrogen Bond

  • An attraction between a hydrogen atom attached to a highly electronegative atom. (F, O, or N) and a nearby electronegative atom in another molecule.
  • Special kind of dipole-dipole interaction.
  • Strongest of the dipole-dipole interaction.
• Ion-Dipole

  • Ion contains unequal number of protons and electrons.
  • Dipole contains 2 charges, where one side is positive and the other one is negative. (Polar)
• Ion-Induced Dipole

  • When an ion is placed next to nonpolar molecule, the ion causes it to be dipole. This dipole is temporary.
  • Induced-Dipole: Non-Polar (equally distributed)
• London Dispersion Force

  • Induced dipole – Induced dipole
  • Dominant force between nonpolar (uncharged)
  • Weakest bond
  • Energy: 0.5 – 1kcal/mole
• Debye Induction Force

  • Dipole – Induced dipole
  • Forced between polar (charged) and nonpolar (uncharged)
  • Energy: 1 – 3kcal/mole
• Keesom Orientation Force

  • Dipole – Dipole
  • Force between 2 polar (charged)
  • Energy: 1 – 7kcal/mole
• For ionic bond:

  Electrostatic interactions get stronger as the charges increases and weaker as the size of ions increases.

  • The higher the charge, the stronger the bond.
  • The bigger the atom, the weaker the bond.
• The higher the electrostatic interaction, the higher the boiling point and the melting point.
• Strength of interactions from highest to lowest

  Ionic bond > Covalent bond > Ion-Dipole > H-Bond > Keesom > Debye > London
• The higher the strength of the interactions, the higher the boiling point and melting point
• Induced dipole is nonpolar, uncharged molecule.
• Dipole is polar, charged molecule.