Marshmallow Models

This experiment is designed to teach students how to make the molecules and ions out of marshmallows and Redhots. The students should leave the lesson understanding that not all the molecules apply to the simple rules. There can be differences when the chemistry of the atoms will become more stable at lower energy states. The bonus of this lesson, like any lesson involving food, is that the students can eat what they create. The realization is that it is not a "healthy" snack but it is one that the students can enjoy as a treat once in awhile.

This lesson comes in about chapter five in the book and is the fifth unit that I will cover in their year. They will have gone through the rules of electron arrangement with the more common molecules, but will not have done anything too extraordinary.
Experiences they will have had before will be more directed labs. Directed labs are where I tell them what to do and then they go and do it. In this lab I will give them the different molecules or ions that I want them to make and see what they come up with. Then ask them to apply the simple rules to the different atoms. This is a slight adjustment in my teaching style and therefore it could be different for me but also for the students.

This lesson follows a traditional ball and stick diagram lab. Start the lesson by going over how the hybrid orbitals work. Introduce it as a game, stating as always the rules first. Most of the simple rules are that the more electronegative elements will pair some of the single electrons and fill boxes, leaving other boxes to fill with full pairs from other electrons. I also introduce the idea that those elements with electronegative numbers want to take other electrons from other elements as well. We call it sharing but really it is not. Then the big rule that is very hard for the students to understand; You can have more than four bonds coming out of central atom, meaning that it violates the octet rule that the students have grown to love.
After the new rules have been explained, go through a couple examples on the board with them and show them how the box or orbital notation should look. Use simple ones to start out and then move into more complex examples. At the same time ask the students, what should this molecule look like? To keep the lesson simple explain that electron pairs want the fewest 90 degree angles with others. The second rule to explain is that the big molecules want the most space. Finally, explain to the students that when you have hybrid orbitals they are really just combinations of the smaller ones we know.
Once the lesson explanations have been completed then it is time to move to the fun part: the lab itself. Hand out a sheet containing various polyatomic ions and acids. Ask the students to use marshmallows and Redhots to construct their molecules. It is recommended for the lesson to buy two different types of marshmallows; large marshmallows represent the central atom, small marshmallows represent attached atoms, and the Redhots are electrons. Use toothpicks to stick everything together and then let them go and explore. I recommend that you have the molecules or ions build off one another, introducing a new idea at each of the steps. During the lesson walk around and check student's progress asking questions and answering questions with questions that guide the students in the correct direction. Collect and assess the students worksheets where they should have also drawn their molecules or ions at the end of the lesson.

Materials
 Marshmallows: Large and small
 Toothpicks
 Redhots
 Sheet containing different polyatomic ions or molecules

 The first inquiry part is to ask the students the different puzzles about how they can move the electrons around so they are in the lowest energy state.
 Second, if the regular rules do not apply and we are adding different rules, then what can we change about the way we thought before?
 Finally, what kinds of shapes are we really looking at? Are they new shapes or are you just combining a couple different ones to create a hybrid one?

Students will be assessed on how well they reason out the correct molecule. While I want the students to find the right answer it is not necessarily the main focus of the assessment. The focus is the process they use to come to the correct answer and what steps they take. If the students are working hard to find the correct answer and then apply the previous knowledge, then they have moved forward. My students know from my teaching practices that they will be also tested on this at the end of the unit. This is also another check to ensure that all the students are doing their own work and striving to understand the concepts and not copying their neighbors.

II. Physical Science
A. Structure of matter
6. The student will be able to explain how atoms form compounds through bonding.