Approximate Analogies

Ionic and Covalent Bonds

Teacher:

Mark McGaugh

Context:

I decided to do this activity while going over mixtures and compounds.

Background:

Many students had trouble with knowing when two substances had actually bonded. The class performed activities such as dissolving salt into water, boiling the water away, and seeing the salt left behind. I explained the salt had never bonded to the water, but formed a homogeneous mixture. This is when I decided to use the approximate analogies technique.

Task:

I wrote on the board the simple prompt “Ionic bonds are to covalent bonds as __________ are to __________”.I listened to the discussions carefully and even facilitated them at a few points.

Results:

After discussing several examples I realized the concept that was never being mentioned was charge. None of the students grasped that ionic bonds were being held together by two charged particles.

Closing the Loop:

Luckily I had some magnets in the classroom. I explained to the class that each magnet had two ends, one with a positive charge and one with a negative charge. To avoid any unnecessary confusion I mentioned nothing about north and south poles. I passed out the magnets and explained that when like charges were facing one another they magnets repulsed one another and when opposite charges faced one another the magnets came together. To make a connection with ionic bonds I told them that the cations and anions, made by electron transfer, are of opposite charge and are attracted just like magnets. Next I took out some rope and pointed out it was not charged. I explained that covalent bonds electrons were shared, which was like tying two atoms together with a rope, and that covalent bonds have no charge.

Reflection:

The activity cleared up one problem but left another one unsolved, why were they confusing compounds and mixtures?I do know that in the future I will cover electrical charge and get the magnets out at the start of the year.

Source:

Keeley, P,  Eberle, F. &Tugel, J. (2007). Uncovering Student Ideas in Science, Volume 2: 25 More Formative Assessment Probes. NSTA Press

Acknowledgement: The author completed this assessment while a student at Montana State University