Dipole-Dipole and Hydrogen Bonds

  1. Some molecules form areas of positive and negative charge formed through an uneven sharing of electrons (polar covalent bonding). Water is formed with polar covalent bonds between hydrogen and oxygen. Below is water.

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  2. Because part of the molecule is partially positive (not as positive as an ion with a +1 charge) there are attractions between the negative portion of one molecule and the positive portion of another molecule. This attraction forms weak bonds between molecules
  3. When hydrogen is one of the atoms within a molecule that is attracted to the dipole on another molecule, this somewhat stronger dipole-dipole attraction is called a hydrogen bond. The hydrogen bond is the attraction between molecules, not the covalent bond which is formed between hydrogen and an atom from its own molecule. Below are some examples of hydrogen bonding.
    1. The dotted line below show the attraction/hydrogen bond between two water molecules.
      (This video clip, used with permission, was developed at the NYU Scientific Visualization Center.)
    2. To see a 3D view of water and it's hydrogen bonds in motion go to: http://polymer.bu.edu/vmdl/Installers/water/install.htm and follow the instructions for installing the software. (Windows only.)
    3. Hydrogen bonding is also an important factor in helping to shape the structure of larger molecules. DNA is an excellent example. Click here to see how these bonds hold together our double helix.
  4. A molecule can have more than one polar region, so the more polar regions a molecule has, the greater two molecules of this kind will attract to each other.
    5. Name
    Propane
    1-Propanol
    1,3-Propanediol
    Boiling Point
    -42°C
    97°C
    214°C
    Structural Formula
    Surface Charges


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