CHEMISTRY CHAPTER ZERO

Counsel for Teachers

I counsel teachers – in my classes and in workshops – that they should think about the Coca-Cola® strategy. This large and successful soft drink company understands that their advertising must persuade a passive audience to take a desired action. I have been told that the Coca-Cola® strategy states that “It takes 20 reps [of an ad] to start moving the market”. I quoted this at a reception one time, and a fellow attendee [not an academic] said, “Yes, but it takes 8 reps for the audience to know that the ad is running.” My version of this – for a student audience of passive learners – is that we teachers must decide on the concepts that we really want to get across in a semester, and during that semester, we must get 20 reps. Perhaps we start with a substantial introduction, and as the semester goes on, we come back for five minutes, for two minutes, etc to reinforce the concepts.

The Chemistry Chapter Zero approach focuses fundamental concepts—getting students to accept that atoms are real and to proceed from this acceptance to reasoning about molecules, bonding, and reactions. Structure/activity relationships are barely addressed.

So… Make sure that you get 20 reps on the first two fundamental concepts!

My approaches

Student form

When I taught my course in Lab and Demos for Middle School Teachers in Fall 2006, I had each teacher sign an “I am in charge form”. I encourage all users of the Chemistry Chapter Zero materials to take the same attitude.

Models

The “foam atoms” are not atoms, they are models of atoms. Teaching students to make use of the fundamental concept of models is an important task, and it will definitely require [at least] 20 reps!

My functional definition is that “Scientific models are stair steps on the staircase that leads toward the truth.” Slides 4-7 in the “Atoms are fun …” presentation elaborate on this metaphor. Using models well requires skillful teaching. A teacher makes the judgments about how many steps the students must climb during the semester and helps the students learn to climb the steps. Choosing to attempt too many steps and providing ineffective assistance leans to frustration and withdrawal of effort. Choosing too few steps does not provide students with all of the instruction that they deserve. Choosing well can lead to effective teaching and enthusiastic learners.

Sequences and Advice 1. Choose your definition of an atom. I strongly recommend the one given here, and the evidence In Chemistry Chapter Zero is directed toward (1) all materials are made up of indivisible lumps called atoms (AFM) and (2) atoms have different weights (MS).

Some students will have heard about protons, neutrons, and electrons, and when they raise questions with these words in them, one good way to respond is to note that these are models that are further up the staircase, more complex, and more than is needed at this time. Quietly, you are trying to get them to think in your chosen mode and to confront the evidence that you are bringing forth. If pressed, you can also say that you are not ready to bring forth the evidence for protons, neutrons, and electrons just yet.

2. Work first on the lumps concept [and gently defer the weight concept for later]. Do a lab ith the AFM. Get the students to work with the idea that they can use a probe to feel discrete “atoms”, even though they cannot see them with their eyes. The extension of this idea is to introduce images taken with a real AFM, in which the lumps in the images are interpreted as “atomic resolution”. Also work on understanding how real scientists work.

This unit can easily provide practice with the skill of two dimensional graphing. Have the students produce a graph (“picture”) of the arrangement of the foam atoms inside the AFM. The foam atoms are about 1” in diameter, so a piece of paper marked off in 1” x 1” squares will be fine; the students should color in a square if the probe shows “high” and leave it blank if the probe shows “low”.

The students carry out the “laboratory work” under the professional scientist procedure.

Many students will simply put the probe down at one point and then another point, and so on. They will have difficulty presenting what they have measured. However, the graphing exercise described in the previous paragraph proceeds easily once the students get the idea of “raster” measurements [Take a measurement at a point, move the probe a certain distance (parallel to one side of the box), and take another measurement, repeat until the edge of the box is reached, then move over to the next row and repeat the “measure then move” process along the next row.] A real AFM builds up images by rastering the probe.

Teacher notes:

(a) Be sure to arrange the foam atoms at least one diameter apart. In this way the probe will give the students “high” and “low” measurements. With a real AFM the probe diameter is greater than the spacing of the atoms, and more complex interpretation of the measurements is required.

(b) It is easy to prevent one class from tipping off the next period class about the arrangement of the atoms in the AFM. Between periods open the garbage bag and rearrange the atoms – Velcro on flannel makes this easy to do.

3. Next work with the foam atoms in the garbage bag. My student and friend Mary Hillebrand introduced this unit to her regular and honors high school chemistry class by upgrading my scenario:

“A NASA space probe has just returned from Planet Xanadu, and you have been chosen to carry out chemical analyses on the material that NASA brought back. NASA wants to know whether the chemistry of Planet Xanadu is similar to the chemistry we find on Earth. How many different kinds of atoms are there? What types of reactions occur? What sort of molecules can we expect to find?”

The students carry out the “laboratory work” under the professional scientist procedure.

Teacher notes:

The basic set of foam atoms has four types of atoms: (1) light core, loop Velcro, (2) heavy core, loop Velcro, (3) light core, hook Velcro, and (4) heavy core, hook Velcro. I have typically started the unit with six atoms in each garbage bag with at least one of each of the four types of atoms. I have also made sure that at least one pair is bonded together. Thus each set of investigators should find that there are four types of atoms, and that at least one molecule is present.

It is important that the foam atoms seem alike (almost). They are all grey foam, with a solid core, a glue pellet on one end, and Velcro (two types) on the other end. This is intentional. I wanted to suppress irrelevant ways of classifying the atoms: for the foam atoms the only characteristics for classification are weight and bonding type. At one time, I considered color-coding the different types of atoms, but I decided against it. Real atoms do not have color in the conventional sense, and I do not want to teach students to think about the foam atoms – as models for real atoms – as having color.

4. At this point, you might prod them to ask whether the atoms from Planet Xanadu fit into a Periodic Table analogous to the one we have on Earth [or you can skip this and come back to it anytime later]. If you decide to do so, you will gently guide the discussion towards the realization that in the standard periodic table, the columns represent different binding capabilities, and the entries down a column represent successively heavier atoms with the same binding capabilities.

[Please realize that, while the description given above is substantially correct, particularly for the upper half of the periodic table, there are many exceptions. If you get the “columns are different binding” and “rows are the same binding with heavier atoms” concept across to pre-high school students, you will have done good work]

[Note to Periodic Table enthusiasts: I know that we encode must more information into the Periodic Table and that we have a profound explanation for many of the regularities in terms of the atomic number, but I am not trying to develop finished chemists at this point.]

5. Since the students have found there are heavy atoms and light atoms, you can move to work with mass spectrometer. They will find that, when they keep the initial conditions constant, the light atoms travel farther than heavy atoms. You can also explain that this is the way that real scientists determine the weight of individual atoms, which are far too tiny (and light weight) to be weighed with conventional balances.

Note: It requires some skill to get reproducible trajectories with the mass spectrometer. Students will have to practice. Let them discover what they must do to get reproducible distances. Remind them that professional scientists do not step up to a new apparatus and get great data right off the bat – they, too, must learn to operate an apparatus well.

6. Circle back to your definition of an atom and explain that they now have worked with apparatus analogous to the real AFM and mass spectrometer apparatus, and they are prepared to make a serious study of the AFM (“lumps”) and mass spectrometry (“lumps can have different weights”) data on real systems. The take home message is that if they accept the data, and the way of interpreting it, then they have accepted atoms as real.

7. Now the scientific fun can begin. The students think they know how to operate the apparatus and that they know all about the samples from Planet Xanadu. You can come back to the garbage bag chemistry labs, but this time put in a new atom. You might make atoms that have a glue pellet on each end, and thus they cannot bind to either hook or loop Velcro. Are these atoms inert? Where do these atoms fit into the Planet Xanadu periodic table? Push them with questions but also let them stew over the new data. Professional scientists have stew over data, why shouldn’t students get do so, too.

Once they decide that they have a new atom, let them name it. The discoverers of new atoms chose names.

Are you still feeling mischievous? The original set of atoms were made with a glue stick core (light) or ¾” set screw (heavy) so that the weight difference would be sufficient for the students to tell that there are light and heavy atoms, just by hefting them in their hands. You can make atoms of intermediate weights by using ¼” and ½” set screws. Most students cannot reliably tell the relative weights of these intermediate atoms. However, students who have become good with the mass spectrometer apparatus can tell the difference. Give the students a chance to weigh them with the mass spectrometer.

Again, if they discover a new atom, and others who repeat their work confirm their results, then they are allowed to name the new atom. Remember any new atom has to fit into their periodic table (or they have to revise their periodic table).

8. You might also make an atom with Velcro on both ends. If you do so, you must be careful about the chemistry that you present. It is OK to toss in an atom with loop Velcro on both ends. When two atoms with hook Velcro on one end bind to your new atom, you have an analog of calcium chloride—OK.

However if you create a second atom with hook Velcro on both ends, then students can chain the atoms together to make chains of (hook-body-hook) bound to (loop-body-loop) bound to (hook-body-hook) and so on. Similarly, if you create atoms of the form hook-body-loop, they can also chain together. However, these chains do not correspond to normal inorganic behavior in the real Periodic Table. Avoid these examples because you want students eventually to map the chemical behavior they have seen with foam atoms onto the real chemical behavior summarized in the Periodic Table., and you do not want “unreal” things interfering.

9. Do you want to talk about chemical reactions? Balanced reactions? Or limiting reagents. Use your creativity and chemical understanding and stock up the garbage bag laboratories with the right combinations of atoms. Then send the student into the lab to study the chemistry of the system.

10. Of course this isn’t real chemistry. You showed your students data that is far more compelling than the Dalton’s arguments based on weights, and through practice with large scale analogs of the real apparatus, they came to understand how to interpret that data. You helped them learn to see with their minds when they could not see with their eyes. You got your students to accept that atoms are real and to reason about chemical reactions. However, you did not commiserate with colleagues about the failure of your students to master the “mole”, and you avoided counting protons, neutrons and electrons, because you did not want to present that concept without showing students good data for the existence of these particles.

We are all glad that this is Chemistry Chapter Zero. In the published chapters of the textbook, they can learn the real stuff!

 

Please check out the Cautions.

Teaching Professional Science

In each teaching exercise, I try to assign a pair of students to a single apparatus, whether it is a foam atoms/chemistry lab, an AFM, or a mass spectrometer. One student A is assigned as the “doer” and student B is assigned as the “recorder”. A “doer” may not write down the observations, and a “recorder” may not carry out the experiment. Once the pair has essentially finished its task, the pair switches apparatus with another pair. Now student A is assigned as the “recorder” and student B is assigned as the “doer”. Each pair is assigned to check the work of the other pair, just as professional scientists try to repeat each others experiments. If time is available, I then bring all the pairs together into one group, and each pair must report its results at this “scientific meeting”. Sometimes the large group comes to a consensus, and sometimes pairs find that they missed something in their experimental work. If time permits, I allow them to go back to the lab, and repeat their experiment and observations.