To demonstrate how ionic compounds are used to purify synthetic diamonds.
Most chemistry classes study ions. The positive ions are metallic and form by losing electrons and the non-metal elements form negative ions by gaining those electrons.
In NOVA "Diamond Deception" program, they finally used aluminum to attract nitrogen out of the diamond. The nitrogen was making the diamond yellow.
Aluminum has a charge of +3 and nitrogen happens to want to lose three electrons. They are a match made in opposite attraction heaven.
To demonstrate how this works, take two long pieces of clear tape off the roll (about 15 centimeters each). If you bring the non-sticky sides of the tape together, you will notice that they will repel each other.
Then place the sticky side of one of the pieces of tape on a table top and quickly pull it off the surface. By doing so you are changing the charge of the tape. Now you have one piece of tape that is charged one way and the one you have just rippped off the table surface will be charged another way. Bring the two non-sticky sides of the tape together again, and this time they will attract (opposites).
The scientists in the program use this principle by using aluminum to attract nitrogen out of the diamond matrix.
You may want to use in the middle of the NOVA "Diamond Deception" program before the portion of the segment where they discuss using aluminum. Stop the video and ask the students what they know about nitrogen. If you have taught ions, they might be able to tell you that nitrogen is a -3 ion. Tell students to watch for how another ion with a positive charge might play a part. This breaks up the video and keeps the kids on task watching the second half for the application of this idea.
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