An introduction and overview of the NGSS, with a particular emphasis on the science and engineering practices in chemistry.

1. NGSS
Models and Modeling
in the
Chemistry Classroom
Larry Dukerich
Dobson H.S.
Mesa, AZ
CRESMET
Arizona State University
Brenda Royce
University H.S.
Fresno, CA
Gary Abud, Jr.
Grosse Pointe North H.S.
Grosse Pointe, MI

2. 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.

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 stoichiometry 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.
=H
=N
Which of the boxes below correctly shows what the
reaction mixture would look like after the reaction
was complete?
A
B
C
D

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 submicroscopic 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. 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

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

12. 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

13. 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.

14. 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’

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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

21. Preparing the Whiteboard

22. Making Presentation

23. NGSS Practices

24. Practice 1: Asking Questions
and Defining Problems
What Teachers Do?
What Students Do?
24

25. Practice 2: Developing and
Using Models
What Teachers Do?
What Students Do?
25

26. Practice 3: Planning and
Carrying Out Investigations
What Teachers Do?
What Students Do?
26

27. Practice 4: Analyzing and
Interpreting Data
What Teachers Do?
What Students Do?
27

28. Practice 5: Using Mathematics
and Computational Thinking
What Teachers Do?
What Students Do?
28

29. Practice 6: Constructing
Explanations & Designing Solutions
What Teachers Do?
What Students Do?
29

30. Practice 7: Engaging in
Argument from Evidence
What Teachers Do?
What Students Do?
30

31. Practice 8: Obtaining, Evaluating,
and Communicating Information
What Teachers Do?
What Students Do?
31

32. What Could It Look Like???
Lower Ele
Upper Ele
Middle
Level
High
School
Practice 1
Practice 2
Practice 3
Practice 4
Practice 5
Practice 6
Practice 7
Practice 8
32

33. Practices of the NGSS
I noticed…
I wonder…
33

34. How Important Is Energy?
 Topics/Content
 Skills
34

35. A Coherent Approach to Energy
Presentation at the Summer 2003 AAPT Meeting
Larry Dukerich
Dobson HS/Arizona State U
Gregg Swackhamer
Glenbrook North HS, Northbrook, IL

36. Current State of Energy Concept
• Energy is regarded as an abstract quantity,
“invented” for doing calculations
• Treatment of energy is inconsistent from discipline
to discipline
• Students cannot use energy to adequately describe
or explain everyday phenomena
• Students are taught that energy comes in different
forms

37. The Problem with Transforming
Energy
• Focus on “changing one form of energy into
another”1 implies that there are different “kinds” of
energy
• “Forms of energy” locution implies that somehow
energy is changing - diverting attention from the
changes in matter that we can describe
– James Clerk Maxwell argued against “forms of energy” treatment,
calling it the “old theory”
1- American Association for the Advancement of Science, Project 2061 Benchmarks Online,

38. Substance Metaphor
• Substance metaphor focuses attention on energy
storage and transfer
– “Energy is stored in different systems and in different ways in
those systems, and it is transferred by some mechanism or other
from one system to another”2
• Consider information
– “ It would be nonsense to say that hard disk information is
transformed into wire information and then into RAM information
and then into CD information”3
• Use of substance metaphor can integrate the way
physics and chemistry approach energy
2, 3 - G Swackhamer, “Understanding Energy-Insights”

39. Problems with Energy in Chemistry
• Heat regarded as an entity, rather than a
mechanism for energy transfer
• Different variables used interchangeably
– Q - what you can calculate
– E - what you’d really like to discuss
– ∆H - what you can discuss
• Only in college texts is treatment of 1st law of
Thermodynamics more thorough

40. Problems with Energy in Chemistry
• Tenuous connection between kinetic energy and
potential energy - typical examples are from realm
of physics
• Students try to apply energy conservation to
heating or cooling curves
– Kinetic energy changes with temperature
– Potential energy changes on plateaus
– Therefore, energy is shuttling back and forth between kinetic and
potential

41. Problems with Energy in Chemistry
• Role of energy in bonding is muddled
– Rearranging atoms in molecules results in energy change
– But is it kinetic, potential or both?
• Students conclude that somehow bonds store
energy
– ATP
ADP releases energy because “high-energy
phosphate bond” is broken
– View is inconsistent with bond dissociation energy

42. Applying the Substance Metaphor
• Do brief coherent treatment of 1st Law of
Thermodynamics - Modeling Instruction in HS
Physics
E n e r g y F lo w
In itia l
F in a l
E k
FT
E g
E e
D ia g r a m
E k
E g
Ee
E in t
box
0
0
W
• Focus on ways to represent energy storage and
transfer

43. Distinguish between attractions and
chemical bonds
• Both involve electrostatic interactions
• Specificity and directionality of these interactions differ
sufficiently that it is useful to treat them separately
• These interactions are associated with different kinds
of change
– Attractions - physical changes
– Bonds - chemical changes

44. Two Categories of Potential Energy
• In physics, it is useful to subdivide potential energy
into gravitational, elastic and electrical categories
• In chemistry, it is useful to consider two categories
– Interaction - due to van der Waals type attractions
between particles (non-directional & non-specific)
– Chemical - due to bonds within molecules (covalent) or
within crystal lattices (ionic). Bonds are directional and
involve specific particles.

45. Attractions and Energy
• Attractions lower the potential energy of a system of
particles, whether due to
– gravitational forces between macroscopic bodies
– electrostatic forces between microscopic particles
• It always requires energy to separate bound
particles

46. .
Incomplete Representation of Ech
• Standard chemical potential energy diagram (left)
shows only part of the picture
potential energy
activated
complex
zero typically chosen as
energy at very large r
0
activated
complex
BDE-R
BDE-P
reactants
reactants
products
products
BDE = bond dissociation energy

47. Re-scale the Potential Energy Graph
• As we do in physics, we can represent energy
wells (-) as energy bars (+) by moving zero position.
zero typically chosen as
energy at very large r
activated
complex
activated
complex
0
BDE-R
BDE-P
reactants
products
reactants
products
BDE = bond dissociation energy
new zero chosen arbitrarily
these bars represent E ch

48. Reconnect Ek and Ech
•
Particles in system exchange Ek for Ech to rearrange atoms
181 kJ + N2 + O2 ––> 2 NO
Reactants
Ek
Ech
Activated
complex
Ek
Ech
Products
Ek
Ech
– Representation consistent with fact that an endothermic reaction
absorbs energy, yet the system cools

49. Reconnect Ek and Ech
• Whether final kinetic energy of system is greater or
lower depends on difference of chemical potential
energy of reactants and products
Reactants
Ek
Ech
Activated
complex
Ek
Ech
– Here, an exothermic reaction is depicted
Products
Ek
Ech

50. We Need to Keep Track of All of the
Accounts During Change
•
This treatment of energy storage and transfer is consistent
with that used in physics
–
A ball is dropped from rest…
In itia l
E k E g E e
E n e r g y F lo w
D ia g ra m
F in a l
E k
E g
Ee
E in t
ball
Earth
0
•
0
The story would not make sense if we considered only Eg

51. Extend This Treatment to Physical
Change
• What happens during phase change?
– The substance doesn’t change - only the arrangement of
the constituent particles
– We are considering the attractions between molecules, not
the attractions between atoms within the molecules
– Use separate account - Ei, the energy due to interactions

52. Attractions Lower Energy of a
System of Particles
• The more tightly bound the particles, the lower the
energy of a system
– Particles in the solid state adopt the most orderly, lowest
energy configuration
– Energy is required to break down this orderly array (melt
the solid)
– Energy is released when particles in a liquid crystallize
into an orderly array (freeze).

53. How is the Energy Stored?
• What are you getting for your energy dollar?
– What is the added energy doing if the temperature of the
system is not increasing?
– It must be overcoming
attractions between the
particles
– The particles are less
tightly bound in liquid phase
– Interaction energy stored is related to ∆Hf and mass of
system

54. During evaporation
• Particles in the liquid require energy input in order
to overcome attractions and become widely
separated in the gas phase.
• Unless energy is supplied to the system, energy for
this change must come from another account, Ek
• Particles in remaining liquid become cooler
(lower Ek)

55. Keeping Track of Energy During
Chemical Change
A coherent way to treat energy in
chemical reactions
55

56. The Conventional Approach
• Treatment of energy in reactions is vague
• Where/how is energy stored is left
unanswered
• How energy is transferred between system
and surroundings is ignored
56

57. Modeling Approach
• Use energy bar diagrams to represent energy
accounts at various stages of reaction
• Provide mechanism for change
• Connect thermal and chemical potential
energy
• Focus on what is happening during the course
of the reaction
57

58. Endothermic reaction
• How do you know on which side to write the
energy term?
• If you had to supply energy to the reactants, the
products store more energy
energy + CaCO3 → CaO + CO2 (g)
• If uncertain, use analogy from algebra
If 3 + y = x, which is greater, y or x?
• Consistent with generalization that separated
particles have more energy
58

59. Endothermic reaction
• This is the standard energy diagram
found in most texts.
• But it doesn’t tell the whole story.
59

60. Energy Bar Charts
• Show energy transfers between
surroundings and system
• Allow you to consider other energy
accounts
60

61. Consider role of Eth
• How does heating the reactants
result in an increase in Ech?
• Energy to rearrange atoms in
molecules must come from collisions
of molecules
• Low energy collisions are unlikely to
produce molecular rearrangement
61

62. Heating system increases Eth
• Hotter, faster molecules (surroundings) transfer
energy to colder, slower molecules (system)
• Now reactant molecules are sufficiently
energetic to produce reaction
62

63. Now reaction proceeds
• During collisions, particles trade Eth
for Ech as products are formed
• After rearrangement, resulting particles move
more slowly (lower Eth).
63

64. Consider all steps in process
1.Heating system increases Eth of reactant
molecules
2.Energy is transferred from Eth to Ech now
stored in new arrangement of atoms
64

65. Exothermic reaction
• How do you know on which side to write the
energy term?
• If energy flows from system to surroundings, then the
products must store less Ech than the reactants
•
CH4 + 2O2 → CO2 + 2H2O + energy
65

66. Exothermic reaction
• CH4 + 2O2 → CO2 + 2H2O + energy
• Place energy bars for Ech
• Postpone (for now) examination of energy required to
initiate reaction.
• Like consideration of the motion of a ball the moment it
begins to roll downhill - don’t worry about initial push.
66

67. Exothermic reaction
• Now take into account changes in Eth
• When reactant molecules collide to produce
products that store less energy, new molecules
move away more rapidly
67

68. Exothermic reaction
• System is now hotter than surroundings;
energy flows out of system until thermal
equilibrium is re-established
68

69. Consider all steps in process
1. Decrease in Ech results in increased Eth
2. System is now hotter than surroundings
3. Energy eventually moves from system to
surroundings via heating
69

70. Contrast Conventional Diagram
• This is the standard energy diagram found in
most texts.
• But, again,it doesn’t tell much of the story.
70

71. But what about energy used
to start reaction?
• Save activation energy for later - in the
study of reaction kinetics
• If this really bothers you, ask yourself how the
energy used to start the reaction compares to
energy released as the reaction proceeds.
71

72. What about a spontaneous
endothermic process?
• When NH4Cl dissolves in water, the
resulting solution gets colder
• What caused the Eth to decrease?
• Some Eth of water required to separate
ions in crystal lattice.
• Resulting solution has greater Ech than
before
72

73. Reaction useful for cold-packs
• The system trades Eth for Ech
• Eventually energy enters cooler system
from warmer surroundings (you!)
73