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Lesson 6:

What’s in an Atom?

Concepts conveyed | Materials | Procedure | Benefits | Resource

Concepts conveyed:

The purpose of this classroom demonstration is to illustrate forces between charged materials. Materials become charged when they gain electrons in excess of the number of protons, or when they lose electrons relative to the number of protons in an atom.

Materials:

(for one group of students)

  • 1 paper hole punch
  • 1 piece of notebook paper
  • 2 balloons (must be small enough to hold in your hand)
  • 1 clear plastic drinking cup
  • 1 nickel
  • 1 flat toothpick

Procedure:

This demonstration should be preceded with a discussion on the atomic theory, electrons, and protons.

Part 1: Paper Hop

Use the hole punch to cut 15 to 20 small circles from a piece of paper. (Colored sheets of paper are more exciting.) Separate the circles and spread them on a table. Inflate the balloon and tie it. Rub the balloon against your hair, about five stokes. (Note: It is important that your hair is clean, dry, and free from oil.) Hold the balloon close to, but not touching, the paper circles. The paper circles will hop towards the balloon. This is due to the attraction between the excessive electrons on the balloon (from the hair) and the relatively more positively charged paper circles. The attraction is strong enough to overcome the force of gravity.

Part 2: Do Not Touch

Stand the coin up on its edge on a flat surface. Balance the flat toothpick (in the same plane as the coin) across the top of the coin. Carefully cover this balanced combination with a clear plastic cup. “Charge” an inflated balloon by rubbing it back and forth against your hair several times. (Note: The hair must be clean and free of oil.) Hold the charged balloon near the plastic cup and slowly move it around the cup. The toothpick will move. The attractive forces between the negatively charged balloon (excess electrons) and the more positively charged toothpick atoms are strong enough to move the toothpick. Thus,overcoming the friction between it and the nickel. (Note: Gravity is not a consideration in this experiment, unlike the first experiment.)

Benefits:

  • The instructor can ask for student volunteers to help with the demonstration. This will help the students to become an active part of the discussion.

Resource:

  • VanCleave, J. P. In Chemistry for Every Kid; Sobel, D., Ed.; John Wiley & Sons: New York, 1989; pp 8-11.