[The structure of matter] may have the most implications for students' eventual understanding of the picture that science paints of how the world works. And it may offer great challenges too. Atomic theory powerfully explains many phenomena, but it demands imagination and the joining of several lines of evidence. Benchmarks for Science Literacy

ven though there is a good argument for a total restructuring of high school science, when I first heard of the effort to start with physics and then introduce chemistry and biology, I was appalled.

It's not that this sequence doesn't make better sense; modern biology is built on chemistry and both subjects are built on physics. How can a student, for instance, understand protein structure without understanding solubility, a key concept of chemistry that depends on the physics of electrostatics at the molecular level? But the flaw in the proposal is that high school physics, as usually taught, is almost irrelevant to chemistry and biology. Physics is almost always synonymous with classical Newtonian mechanics: projectiles, pulleys, inclined planes and the like. For physics to be of any use to chemistry and biology, it must address atomic physics: the structure of atoms and molecules and their interactions, material which is rarely part of any introductory physics course at the high school or college level, even the overrated AP Physics curriculum.

So, it must be understood that implicit in the proposal to reverse the sequence of high school science courses is a totally new conception of physics, something the leading advocates of the "physics first" concept, such as Nobel Prize winner Leon Lederman, agree is necessary.

The new sequence allows biology and chemistry to be based on an atomic view of the world. The new role for physics is to provide that perspective. This is a huge challenge that will require far more curriculum change for physics than is needed in biology or chemistry. An approach is needed that is accurate without being overly mathematical. Much of atomic physics can be treated classically, but students also need an acquaintance with the strange world of quantum mechanics. Although students will have only limited mathematical skills to analyze these concepts, statistical concepts will have to be addressed. The challenge will be to equip students with the important insights while avoiding too great a reliance on mathematics.

This new science curriculum needs to address a set of topics that currently lacks an accepted name. I recommend using the term "atomic-scale models." This is better than "atomic theory," as used in the Benchmarks for Science Literacy, and similar terms used in the National Science Education Standards that risk confusion because scientists use these to describe the quantum mechanical description of electron orbitals in atoms. "Kinetic molecular theory" (KMT) is widely used in education, but it generally applies only to physical phenomena that do not involve chemical bonds, atomic forces, or atomic level interactions with light. This term should be quietly buried because it covers more than kinetics, applies to atoms as well as molecules, and is a model, not a theory.

While atomic-scale models provide an essential foundation for the new science curriculum, they are difficult to teach. Extensive research shows that using carefully designed instructional strategies, it is possible to teach middle school students KMT. It is questionable, however, whether it's worth the effort because, as usually taught, KMT does not have unifying power and fails to help students reason about related effects, such as thermal conduction, change of state, or the compression of gases. For example, one excellent study found that KMT does not help students understand thermal conductivity and the superiority of the fluid flow model of heat. In another study, prospective teachers failed to use KMT to explain evaporation and condensation. In both studies, the learners were unable to reason from the model.

This inability to reason from the KMT model is not surprising. Most of the reported successes with KMT test only whether students can produce the correct atomic-scale description for a given macroscopic situation. This measures memorization, not reasoning. For instance, students in one study learned to draw reasonably accurate atomic-level pictures of solids, liquids, and gasses, but there was no evidence that they could use these pictures to explain or predict phenomena. Doubtless, this "theory" appears to students as extra mental baggage that is difficult to remember because it is counterintuitive and doesn't explain anything. Because of these difficulties, the national education standards recommend delaying the introduction of atomic-scale models until the end of eighth grade or the beginning of ninth grade.

While this may be good advice given traditional instructional strategies, computer-based modeling tools can help students understand what is happening at the atomic level. By giving students manipulable computer-based models, we suspect that even young students can understand key concepts of atomic-scale systems. Using these models, students can explore the relationships between atomic forces, random motion, and a wide range of phenomena. Models can be built that demonstrate gas laws, condensation and evaporation, solubility, crystallization, protein conformation, and much more. This should give students a powerful understanding that has a broad range of applicability.

There are at least three software packages (supported by Macintosh and Windows operating systems) that educators can use today:

Interactive Physics. This powerful simulation environment sold by MSC Software can be applied to atomic models. It has the advantage that it is easy to use and modify. Educators on small budgets will appreciate that it can also support instruction in more traditional classical dynamics. In fact, this ability to move between macroscopic mechanisms and atomic-scale atoms and molecules might help remove some of the mystery of the latter. (See illustration above)

StarLogoT. Derived from Logo, this free programming language is optimized to support large numbers of independent "turtles" that can interact according to rules supplied by the user. The fact that it is a language that the user can see and alter makes the models particularly transparent. This may have great value to learners with some familiarity with programming. For the majority of learners who are unfamiliar with programming, models with good user interfaces can be created and shared. One of many models already available is Gas Lab (see also Monday's Lesson). This model can be used to explore a wide range of gas properties. By adding electrostatic forces, an even wider range of atomic models can be built. (Read Uri Wilenksy's article and his Monday's Lesson on StarLogoT).

Molecular Dynamics. This new package was developed by Stark Design specifically to support learning a range of atomic-level ideas. It has a very clean interface and a series of optional modules that illustrate specific concepts using both two- and three-dimensional models. Molecules and bonds are not supported. The full set of modules is pricey, but a free introductory version is available. The lack of documentation and user controls, however, might make this appear as an impenetrable black box to students. You can read about this application in Scientific American.

Each of these modeling packages has drawbacks for teaching atomic-scale concepts. We hope to encourage the developers of these programs to address the specific needs of students in a physics-first curriculum. We suspect that learners need flexible environments like these that support electrostatics, molecular bonds, and interactions with light. Once we study student learning with these environments, our expectations will have a strong empirical foundation.

Robert Tinker is president of The Concord Consortium.
bob@concord.org

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