Models and Modeling
in the High School
Chemistry Classroom
Larry Dukerich Brenda Royce
Dobson HS University HS
Mesa, AZ Fresno, CA
CRESMET
Arizona State University
1

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.
2

“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
3

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 =H
N2 + 3 H2 → 2 NH3 =N
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
4

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.
5

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.
6

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

More
Storyboards
Gas Diffusion:
Where’s The Air?
Aqueous Diffusion:
The 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?
9

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 10

What Do We Mean by Model?
Symbolic Representations
Verbal
Algebraic
Physical Mental
System Model
Diagrammatic
Graphical
Models are representations of structure in a physical
system or process
11

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
12

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.
13

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’
14

Particle Models of Gradually
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
15

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
16

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
17

Reconnect Eth and Ech
 Particles in system exchange Ek 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 18

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
19

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
20

Preparing the Whiteboard
21

Making Presentation
22