Models and Modeling in the High School Chemistry Classroom

1. Models and Modelingin the High SchoolChemistry Classroom Larry Dukerich Modeling Instruction Arizona State University

2. 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.

3. “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

4. 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 NH3The 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?

5. 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.

6. 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.

7. Representation of Matter • Question: “What’s happening at the simplest level of matter?”

8. More Storyboards Gas Diffusion: Where’s The Air? Aqueous Diffusion: The Continuous Model of Matter

9. 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?

10. 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

11. I See It Because I Believe It

12. InstructionalObjectives • 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

13. What Do We Mean by Model? Models are representations of structure in a physical system or process

14. 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

15. 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.

16. 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’

17. 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

18. 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

19. 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

20. 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

21. How to Teach it? 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

22. 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

23. Preparing the Whiteboard

24. Making the Presentation