Lewis/Life - Teaching Techniques

Chapter 3 - Teaching Techniques

A. General Tips
Probably your most formidable tasks with this chapter will be deciding first how much chemistry your students already have and second how much chemistry they need to fulfill the objectives of your course. This chapter is packed with material and many of your students are already afraid of the word chemistry; many of them will be overwhelmed -- particularly the non-science majors.
I suggest you begin your preparation by reading the summary at the end of the chapter. Keep the summary points in mind as you skim through the rest of your course. What are your specific course objectives? Decide what is necessary for your particular class, go back through the text to see how those points are presented, and then teach chemistry accordingly.
This chapter is quite "readable." Lewis does a good job with the presentation; some of my own students did "student reviews" of this chapter for the author and their comments were generally quite favorable. Your students will not have too much difficult with the quality of the material; it is only the quantity that I caution you about, particularly if you have students who have had no exposure to chemistry before.
For your particular class, it may be appropriate to include some of the material in this chapter with other chapters. For instance, you might wish to defer the material on nucleic acids until you reach Chapter 14, Chromosomes. Decide what is best for your students.
You might wish to copy and distribute to your students the Overview of Chapter Objectives flowchart found at the beginning of this Instructor's Manual Chapter.
B. Possible Approaches to the Chapter
Be positive about chemistry. Don't tell your class that chemistry is hard. They've already heard this from everyone else! Interestingly, for many people, once they catch on to the basics of chemistry, they find it amazingly easy and wonder why it took so long to "get it." But before they "got it", they were certain chemistry was absolutely impossible.
I urge you to make liberal use of drawings and props in teaching this chapter.
Use the Mastering Concepts questions within the chapter.
Use ball-and-stick models. If your school does not have molecular models, make some models from marshmallows or fruits and toothpicks. Many of these students need that visual, spatial sense.
I definitely suggest a quiz (or a non-quiz) at the beginning of the next class period after you start your chemistry discussion. Correct the quiz in class (even if you don't collect the points) because it is important to clear up any misconceptions immediately. And there will be some!
C. Hints Related to Specific Chapter Topics
- II. Ask the students if water is a chemical. Many people have the idea that chemicals are necessarily "bad things." They have a difficult time assimilating the idea that everything is made up of chemicals.
- II.B-D. One way to visualize the atom is to think of the "ball-within-a-ball" model. Ask the students to envision a tiny mesh bag filled with red and green marbles. The red marbles are the protons and the green marbles are the neutrons. This tiny bag is suspended within a golf ball. The golf ball represents the innermost electron shell, the shell for row one on the periodic table. The golf ball is suspended in a tennis ball. This ball is the shell for the second row. The tennis ball is suspended in a volleyball, the third shell. The volleyball is suspended within a basketball. And so forth.
- II.B. Students often have trouble with isotopes, often not seeing that any given form of an atom is an isotope. They tend to think that there is one "correct" form (and that that "correct" form is not an isotope) and that all other forms are isotopes. To address this misconception, I suggest you "create" some isotopes.
  Start by using the formula p + n = aw (protons plus neutrons equals atomic weight). Then put a C (for carbon) on the board. Ask how many protons this C has. Under the C put "6 p" and then ask for the atomic weight of carbon. Leave some room beneath your "6 p", draw a line and write 12 beneath the line. Refer back to the formula and ask how many neutrons this atom of carbon has. Between the "6 p" and the line fill in "6 n." State that this is one isotope of carbon, specifically Carbon 12, and put a "12" next to the C.
  To the right of the C-12, write another C. Ask how many protons this atom has. Again write "6 p" and draw a line. Tell them that the weight of this particular atom is 13 and write "13" beneath the line. Ask how many neutrons this particular atom has. Fill in the "7 n" and add the 13 next to the C. Explain that this is Carbon 13.
  Follow this pattern for Carbon 10, and Carbon 14. Explain that all of these are isotopes of carbon.
- II.C. Some purists may argue about the definition of molecule as stated in this section by stating that ionic compounds cannot properly be called molecular. If anyone worries about that, remind that person that the problem is one of semantics (and thus there are varying opinions) and that this is an introductory course.
- II.D. For an overview of bonding, I suggest using a chart such as this:
- III.A. To demonstrate the bonding properties of water, I suggest you do a simple toothpick experiment. Bring in a dish or petri plate full of water. (Use a clear plate so students can see from the edge.) Gently place a toothpick on the water. Show how the toothpick literally sits on top of the water. Sketch this: Encourage students to repeat the experiment at home. Another example of the same phenomenon is an insect walking on water. The surface tension of the water, a direct property of hydrogen bonding, is strong enough to allow the toothpick or the insect to ride on this "bond membrane."
- III.B.1. Ask a few questions, like "A pH of 2 is how many times more acidic than a pH of 4?" The students invariably will want to say 20 instead of 100.
- III.C. Unless your class has had chemistry, I suggest you ask them simply to accept the concepts of heat capacity and heat of vaporization without a lengthy explanation. If you start to go into much detail with this, you will find it necessary to go into much too much detail.
- IV. Show the commonality of dehydration synthesis and hydrolysis. These are recurrent themes present in the formation of all major organic macromolecules. Show how this same theme occurs over and over.
- IV.B. Sketch a glycerol molecule (as per Figure 3.19) and show how the three fatty acids are attached to it (by dehydrations synthesis, of course). Tell the students to keep this structure in mind because they will be encountering phospholipids in the cell membrane.
- IV.B.2. Steroid have gotten a bad rap and it is good that Lewis has used the more generic term, "sterol." ("Steroid" as a classification name is not totally incorrect, and some books do use "steroid" instead of "sterol.") Students are often amazed to learn that hydrocortisone ointment, vitamin D, cholesterol, sex hormones, and anabolic steroids are all in the same family of compounds. They all have the same steroid core and differ only in their side chains.
- IV.C.1. The biggest problem students have with proteins is the immensity of the concept. They tend to think of proteins either as those nebulous molecules floating in the world of ideas or as fibers of muscle tissue. Many people have difficulty grasping the idea that the functional polypeptide is a protein.
  Proteins can be classified in many ways but according to function the simplest way to classify them is as structural or regulatory.
- IV.C.2. A simple way of demonstrating the four conformational structures of the protein is to use something like I do when I use my shell necklace. This necklace has numerous different types of shells all strung together. I hold it up (in long form, not clasped together) and state that the string connects the carboxyl group with the amine group, right on down the line. The individual shells types sticking out from the string are the R groups.
  The order of the shells is the primary structure. The way the shells are spatially in relation to one another is the secondary structure. (I show how I can physically move these R groups so they are not always the same.) Then I gently let the necklace fall on my hand and state that the way it lays over itself is its tertiary structure. I further explain that because of such attractions as hydrogen bonds and sulfide bonds, this structure will remain constant under a given set of conditions. To demonstrate the quaternary structure, I explain that quaternary implies two or more necklaces so if I had two I would hold them up together and let them fall together on my hand. The way the two strands interacted would be my quaternary structure.
  That necklace analogy may sound a bit simplistic. But, I have had more than one student come back more than a year later and say that recalling the necklace made the concept perfectly clear when working with proteins in more advanced courses.
- V.D. Sketch a chart such as this to show the commonality between the nucleotides and the nucleic acid and the ATP. Some students do not see the relationship. I have put "Etc." on this chart. If you use this concept and go into details on some of the energy charts, you could refer back to this chart and show that the "Etc." includes such molecules as GTP.