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Hydrogen Bonding Activity

   
  Introduction: Have you ever gotten clothes out of a dryer and found that some are "stuck" together? Or, have you tried to "stick" a balloon to the ceiling after rubbing it against your hair or a sweater? (If not, try it!! The balloon trick is fun.) Both of these examples rely on two simple facts of nature:
  1. Electrons are relatively easy to remove from atoms.
  2. Some materials (or atoms) attract electrons better than others.
These ideas are important in hydrogen bonding and can be demonstrated by simply sticking two pieces of tape together as described below.

Materials: Before you begin, you will need to do the following:

  • Get some clear plastic tape (sometimes called Scotch Tape).
  • Find a hard smooth surface nearby on which you can temporarily stick some tape, maybe a desk top, a table (not wood), a window, the floor, or a door.
Action: Follow these steps:

  1. Tear off two pieces of tape. Make them about as long as your finger.
  2. Fold the top little bit of each tape down so that it sticks to itself.
  3. Press one piece of tape down on a hard smooth surface (such as a table top.) Lay the second piece of tape directly on top of the first, with the sticky side down and the little folded parts together. The picture below shows how this looks.

  4. Rub the top piece of tape so that it is well stuck to the one on the bottom. (While you are doing this, something has happened that you can't see with your eyes. Try to imagine a whole bunch of electrons that are part of the atoms that make up the clear plastic tape. These electrons aren't stationary; they are migrating toward the material that attracts them most. Can you see a picture of this in your mind?) Before doing the demonstration, make a guess; will the glue side of the tape or the smooth plastic side attract electrons more?
  5. Leaving the two pieces of tape stuck together, peel them both off the smooth surface.
  6. Grab the folded parts of each piece of tape and very quickly rip the two pieces apart.

  7. Now, slowly bring the two pieces of tape nearer and nearer to each other without touching them together.

  • What happened?
  • Did the two pieces of tape behave this way before you pressed them together?
Explanation: If the demonstration worked and the two pieces of tape became attracted to each other, then you saw the effects of electrostatic attraction. In other words, because the electrons moved toward one side of the tape, this side became negatively charged. The migration of electrons left the other side of the tape with a deficiency of electrons, causing it to become positively charged. Opposite charges attract, so the two oppositely charged pieces of tape were attracted together.

Extension: From this demonstration alone, it is not possible to know if the glue side or the plastic side of the tape is better at attracting electrons (i.e., negatively charged). Can you think of a way to determine which side of the tape was a better attractant for electrons?

To more demonstrations

Return to Kevlar--Clue 4

   
   
 

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