Models and Modeling in the High School Chemistry Classroom Larry Dukerich Modeling Instruction Arizona State University We’re here to tell you about the application of the Modeling Method of instruction (first developed for use in high school physics) to the high school chemistry course.

Traditional Instruction Presumes two kinds of knowledge: Facts and ideas - things packaged into words and distributed to students. Know-how - skills packaged as rules or procedures. Assumes students will see the underlying structure in the content. First some background on what is the problem with conventional instruction. Bullet-1 David Hestenes refers to the first as “factons”, what students record and try to reproduce on tests. The 2nd category he calls “factinos”, stuff that passes unimpeded through students’ heads.

“Teaching by Telling” is Ineffective Students… Systematically miss the point of what we tell them. do not have the same “schema” associated with key ideas/words that we have. do not improve their problem-solving skills by watching the teacher solve problems Our students don't share our background, so key words, which conjure up complex relationships between diagrams, strategies, mathematical models mean little to them. To us, conservation of energy makes us accountants, keeping track of energy in system and surroundings. To students, it’s a definition to recite. All my careful solutions of problems at the board simply made ME a better problem-solver.

Algorithms vs Understanding What does it mean when students can solve quantitative problems, but cannot answer the following? Nitrogen gas and hydrogen gas react to form ammonia gas by the reaction N2 + 3 H2  2 NH3 The box at right shows a mixture of nitrogen and hydrogen molecules before the reaction begins. Which of the boxes below correctly shows what the reaction mixture would look like after the reaction was complete? There is a big difference between the mathematical ‘game’ of stoichiometry and being able to describe what is going on in a reaction vessel. Ideally, students would do both simultaneously.

How Do You Know? All students know the formula for water is H2O. Very few are able to cite any evidence for why we believe this to be the case. What does it mean to be ‘2 parts hydrogen and 1 part oxygen’? There can be a very real gap between their words and how they perceive matter at the microscopic level (for more than just water!!)

Do They Really Have an Atomic View of Matter? Before we investigate the inner workings of the atom, let’s first make sure they really believe in atoms. Students can state the Law of Conservation of Mass, but then will claim that mass is “lost” in some reactions. When asked to represent matter at sub-microscopic level, many sketch matter using a continuous model. The real roadblock to many students is not which atomic model they use, but whether they have ANY sufficiently developed atomic model that is consistently applied. SAMPLE STUDENT WORK NEXT

Representation of Matter Question: “What’s happening at the simplest level of matter?” The steel wool turns color when heated. Some think that some part of the gas from the burner flame in now trapped in the wool, but few actually drew simple particles that combined to form new substances.

More Storyboards Gas Diffusion: Where’s The Air? Aqueous Diffusion: The Continuous Model of Matter Gas particles move very rapidly, yet the scent of popcorn flavoring takes a while to reach the back of the room. In the bottom storyboard students revert to a continuous model of matter .

Where’s the Evidence? Why teach a model of the inner workings of the atom without examining any of the evidence? Students “know” the atom has a nucleus surrounded by electrons, but cannot use this model to account for electrical interactions. What’s gained by telling a Cliff’s Notes version of the story of how our current model of the atom evolved? This is why I have a problem with texts that ruin the story by going to the end of the book right away. If we want students to see science as more than a collection of facts, then we have to connect our models to the evidence that leads to them.

Seeing is Believing? Because students have trouble relating microscopic and macroscopic views, we start our discussion with the atom and bypass the traditional historical approach taken by many texts. (This is not to say that we do not value the study of the history of chemistry; in fact, we believe that history helps the material come alive.) Pictures from scanning tunneling microscopes can now “show” us atoms. Therefore, we begin with “We believe in atoms because we can see them.” “Teaching Tip” from World of Chemistry, Zumdahl, Zumdahl, DeCoste, McDougall Littell, 2007

I See It Because I Believe It If we didn’t believe in atoms, we wouldn’t be convinced by this little bumps on the metal foil.

Instructional Objectives Construct and use scientific models to describe, to explain, to predict and to control physical phenomena. Model physical objects and processes using diagrammatic, graphical and algebraic representations. Recognize a small set of particle models as the content core of chemistry. Evaluate scientific models through comparison with empirical data. View modeling as the procedural core of scientific knowledge What should we teach? Our students should learn to do the following: They should see that physics involves learning to use a small set of models, rather than mastering an endless string of seemingly unrelated topics.

What Do We Mean by Model? This word is used in many ways. The physical system is objective; i.e., open to inspection by everyone. Each one of us attempts to make sense of it through the use of metaphors. Unfortunately, there is no way to peek into another’s mind to view their physical intuition. Instead, we are forced to make external symbolic representations; we can reach consensus on the way to do this, and judge the fidelity of one’s mental picture by the kinds of representations they make. So the structure of a model is distributed over these various representations; later we’ll provide some specific examples. Models are representations of structure in a physical system or process

Why Models? Models are basic units of knowledge A few basic models are used again and again with only minor modifications. Models help students connect Macroscopic observations Sub-microscopic representations Symbolic representations Students WILL work from a model of matter** - the question is which model and is it a rigorous, scientifically supported model applied consistently to all situations **refer to storyboards

Why Modeling?! To help students see science as a way of viewing the world rather than as a collection of facts. To make the coherence of scientific knowledge more evident to students by making it more explicit. Models and modeling figure prominently in the NGSS. Emphasis on points 1 and 2.

Uncovering Chemistry Examine matter from outside-in instead of from inside-out Observable Phenomena  Model Students learn to trust scientific thinking, not just teacher/textbook authority Organize content around a meaningful ‘Story of Matter’ Herron writes, “Pick any introductory chemistry text and look at it. Is it organized according to a logical order or a psychological order? Does it begin with phenomena that are closely related to the experience of students? Does it introduce abstract notions such as atoms, molecules, ideal gases, bonding and kinetic theory only when the student senses a need for some way to explain what he has already observed? “

Particle Models of Increasing Complexity Begin with phenomena that can be accounted for by simple BB’s Conservation of mass Behavior of gases - KMT Recognize that particles DO attract one another “Sticky BB’s” account for behavior of condensed phases Reference: “The Story So Far” doc

Models Evolve as Need Arises Develop model of atom that can acquire charge after you examine behavior of charged objects Atom with + core and mobile electrons should explain Conductivity of solutions Properties of ionic solids There’s little sense in introducing inner workings of the atom until the students are ready to examine these phenomena.

Energy - Early and Often Make energy an integral part of the story line Help students develop a coherent picture of the role of energy in changes in matter Energy storage modes within system Transfer mechanisms between system and surroundings Teachers have told me that they postpone the treatment of energy or limit their treatment to Q = m c (delta) t because they feel uncomfortable about it. But the role of energy in change sin matter figured prominently in the NSES and now in the NGSS.

Reconnect Eth and Ech Particles in system exchange Eth for Ech to rearrange atoms 181 kJ + N2 + O2 ––> 2 NO Representation consistent with fact that an endothermic reaction absorbs energy, yet the system cools Diagrammatic representations help make the concepts of energy storage and transfer more explicit.

How to Teach it? cooperative inquiry vs lecture/demonstration constructivist vs transmissionist cooperative inquiry vs lecture/demonstration student-centered vs teacher-centered active engagement vs passive reception student activity vs teacher demonstration student articulation vs teacher presentation lab-based vs textbook-based Here are the key ways in which the modeling method differs from conventional instruction. Students present solutions to problems which they have to defend, rather than listen to clear presentations from the instructor. The instructor, by paying attention to student’s reasoning, can judge the level of student understanding.

Be the “Guide on the Side” Don’t be the dispenser of knowledge Help students develop tools to explain behavior of matter in a coherent way Let the students do the talking Ask, “How do you know that?” Require particle diagrams when applicable

Preparing the Whiteboard As students prepare whiteboards, they help each other work out the details they may have been confused about.

Making the Presentation When students present their whiteboards, they articulate their thinking on the subject.