Bonding Unit - Oakland Schools

Bonding Unit
Teaching Tools: Covalent Bonds and Polarity
Purpose
This demonstration is used to help visualize a polar versus nonpolar covalent bond.
Construction
Straighten a large paper clip. Pass it through the centers of two Styrofoam balls. Bend
a hook at one end of the wire, slide the balls onto the hook, bend a hook at the other
end of the wire close to the ball, and cut off the excess wire. Find two identical rubber
bands, and attach one to each hook. As the balls will represent electrons, you might
wish to draw minus signs on each. Prepare a second identical model, except that one
rubber band must be strong and one must be weak, but the same length.
Procedure
To demonstrate a nonpolar covalent bond, mark the back of each hand with an “H”.
Grasp each rubber band of the first model (the one with identical rubber bands) with
one finger, and pull to stretch the rubber bands. Notice that the “electrons” are
attracted equally by both atoms.
To demonstrate a polar covalent bond, mark the back of your right hand with “H” and
the back of your left hand with “F”. Grasp the second model so that the weaker rubber
band is held by the right “H” hand and the stronger rubber band is held by the left “F”
hand. Notice that when you pull to stretch the rubber bands, the “electrons” are pulled
closer to the F atom.
You may want to point out the limitations of the model; the chemical bonds result from
electrical attraction (not rubber bands) and that the electrons are constantly moving at
a high speed in random motion. The model is not to scale.
Source
Guenther, Al. Practical Activities for Strengthening Your Teaching of Chemistry Concepts
in Your Science Classes. Bellevue: Bureau of Education and Research, 2003.