Demonstration 3: Magnetic Analogy for Bonding Forces

To demonstrate the electrostatic attraction and repulsion between like and unlike charges using a magnetic analog.

• 4 ceramic ring or disk magnets
• overhead projector and screen

Begin the demonstration by showing on the overhead projector that like poles repel and unlike poles attract. Draw an analogy to attraction and repulsion between electric charges.

Set up two pairs of magnets so that each pair is attractive. This will illustrate the attraction between the nucleus and an electron. Move one pair into the center of view. Then approach with the other pair in so that one "nucleus" approaches the other "nucleus." No attraction is observed. Move this pair so that the "electrons" are between the two "nuclei." This leads to a stable arrangement.

With the stable arrangement in the center, show that if either "electrons" or "nuclei" are forced closer together, they repel. Thus an "equilibrium distance" between particles with like charges is created.

Remarks

This demonstration takes 15 min. or less to prepare and present, depending upon availability of disk or circular magnets. The demonstration should be presented when covalent bonding is introduced.

Practice with the magnets prior to doing the demonstration. It requires patience to move the magnets carefully to show formation of a "bond". Either ring or disk magnets may be used, but the magnets should be face-magnetized, that is, faces should be the poles. It's possible to use ring magnets to represent the nuclei and disk magnets to represent the electrons. In either case, use larger-diameter magnets for nuclei and smaller-diameter magnets for electrons.

The materials may be saved and used many times. Ceramic magnets are somewhat fragile and should not be dropped. Edmund Scientific, Radio Shack, and similar sources can supply these magnets. Disk magnets are also frequently available at hobby shops and craft shops.

Point out that this is an analogy to the electrostatic forces that cause a covalent bond to form. Both magnetic and electrostatic forces behave the same way; like charges or poles repel and unlike ones attract. Point out that a "nucleus-electron" pair is stable because there's only one attractive force and no repulsive forces. When two pairs approach, new attractive forces arise between the "nucleus" of one pair and the "electron" of the other pair, and vice versa. New repulsions also are present between the two "nuclei" and the two "electrons." The result is four attractions but only two repulsions, hence the two pairs form a stable arrangement.

	TABLE OF CONTENTS	TOPIC OVERVIEW	CONCEPT/SKILLS DEVELOPMENT	LINKS/CONNECTIONS	EXTENSIONS