Models and Modelingin the High School

Chemistry Classroom

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Larry DukerichModeling InstructionArizona State University

Traditional Instruction2

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.

“Teaching by Telling” is Ineffective

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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

Algorithms vs Understanding

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What does it mean when students can solve quantitative problems, but cannot answer the following?

= H

= N

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?

A B C D

How Do You Know?5

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.

Do They Really Have an Atomic View of Matter?

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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.

Representation of Matter7

Question: “What’s happening at the simplest level of matter?”

More Storyboards

Gas Diffusion: Where’s The Air?

Aqueous Diffusion:

The Continuous Model of Matter

Where’s the Evidence?9

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?

Seeing is Believing?10

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 It11

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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

Instructional Objectives

What Do We Mean by Model?

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Models are representations of structure in a physical system or process

Symbolic Representations

PhysicalSystem

MentalModel

Verbal

Algebraic

Diagrammatic

Graphical

Why Models?14

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

Why Modeling?!15

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.

Uncovering Chemistry16

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’

Particle Models of Increasing Complexity

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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

Models Evolve as Need Arises

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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

Energy - Early and Often19

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

Reconnect Eth and Ech

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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

How to Teach it?21

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

Be the “Guide on the Side”22

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 Whiteboard23

Making the Presentation24