Models and Modeling in the High School Chemistry Classroom

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Models and Modelingin the High SchoolChemistry
Classroom

Larry Dukerich Dobson HS Mesa, AZ CRESMET Arizona
State University
Brenda Royce University HS Fresno, CA
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The Problem with 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.

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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

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Algorithms vs Understanding

• What does it mean when students can solve
  stoichiometry 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?
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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.

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Do They Really Have an Atomic View of Matter?

• Before we investigate the inner workings of the
  atom, lets 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.

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Representation of Matter

• Question Whats happening at the simplest level
  of matter?

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More Storyboards Gas Diffusion Wheres The
Air? Aqueous Diffusion The Continuous Model
of Matter
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Wheres 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.
• Whats gained by telling a Cliffs Notes version
  of the story of how our current model of the atom
  evolved?

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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

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What Do We Mean by Model?

• Models are representations of structure in a
  physical system or process

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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
• Microscopic representations
• Symbolic representations

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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 Systems are explicitly recognized as
  major unifying ideas for all the sciences by the
  AAAS Project 2061 for the reform of US science
  education.

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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

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Particle Models of Gradually Increasing Complexity

• Begin with phenomena that can be accounted for by
  simple BBs
• Conservation of mass
• Behavior of gases - KMT
• Recognize that particles DO attract one another
• Sticky BBs account for behavior of condensed
  phases

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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

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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

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Reconnect Eth and Ech

• Particles in system exchange Ek for Ech to
  rearrange atoms
• 181 kJ N2 O2 gt 2 NO
• Representation consistent with fact that an
  endothermic reaction absorbs energy, yet the
  system cools

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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
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Be the Guide on the Side

• Dont 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

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Preparing the Whiteboard
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Making Presentation