NGSS Chemistry Webinar

NGSSNGSSModels and ModelingModels and Modeling

in thein theChemistry Chemistry ClassroomClassroom

Larry DukerichDobson H.S.Mesa, AZCRESMETArizona State University

Brenda RoyceUniversity H.S.Fresno, CA

Gary Abud, Jr.Grosse Pointe North H.S.Grosse Pointe, MI

The Problem with The Problem with Traditional InstructionTraditional Instruction Presumes two kinds of knowledge:Presumes two kinds of knowledge:

Facts and ideasFacts and ideas - - thingsthings packaged packaged into words and distributed to students.into words and distributed to students.

Know-howKnow-how - skills packaged as rules - skills packaged as rules or procedures.or procedures.

Assumes students will see the Assumes students will see the underlying structure in the content.underlying structure in the content.

““Teaching by TellingTeaching by Telling”” is is IneffectiveIneffective

Students…Students… Systematically miss the point of what we Systematically miss the point of what we

tell them.tell them. do not have the same do not have the same ““schemaschema”” associated associated

with key ideas/words that we have.with key ideas/words that we have. do not improve do not improve their their problem-solving skills problem-solving skills

by watching the by watching the teacherteacher solve problems solve problems

Algorithms vs Algorithms vs UnderstandingUnderstandingAlgorithms vs Algorithms vs UnderstandingUnderstanding

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

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.

Which of the boxes below correctly shows what the reaction mixture would look like after the

reaction was complete?

How Do You Know?How Do You Know?

All students know the All students know the formula for water is Hformula for water is H22O.O.

Very few are able to cite Very few are able to cite any evidence for why we any evidence for why we believe this to be the case.believe this to be the case.

All students know the All students know the formula for water is Hformula for water is H22O.O.

Very few are able to cite Very few are able to cite any evidence for why we any evidence for why we believe this to be the case.believe this to be the case.

Do They Really Have an Do They Really Have an Atomic View of Matter?Atomic View of Matter? Do They Really Have an Do They Really Have an Atomic View of Matter?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.

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 MatterRepresentation of Matter

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

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

More More StoryboardsStoryboards

Gas Diffusion: Gas Diffusion: WhereWhere’’s The Air?s The Air?

Aqueous Diffusion: Aqueous Diffusion:

The Continuous The Continuous Model of MatterModel of Matter

Where’s the Evidence?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?

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?

Construct and useConstruct and use scientific models to describe, scientific models to describe, to explain, to predict and to control physical to explain, to predict and to control physical phenomena.phenomena.

Model physical objects and processes using Model physical objects and processes using diagrammatic, graphical and algebraic diagrammatic, graphical and algebraic representations.representations.

Recognize a small set of particle models as the Recognize a small set of particle models as the content corecontent core of chemistry. of chemistry.

Evaluate scientific models through comparison Evaluate scientific models through comparison with empirical data.with empirical data.

View modeling as the View modeling as the procedural coreprocedural core of scientific of scientific knowledgeknowledge

InstructionalInstructional ObjectivesObjectives

What Do We Mean by What Do We Mean by Model?Model?

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

Why Models?Why Models?Why Models?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

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

Why modeling?!Why modeling?! To help students see science as a way of To help students see science as a way of

viewing the world rather than as a collection of viewing the world rather than as a collection of facts. facts.

To make the To make the coherencecoherence of scientific knowledge of scientific knowledge more evident to students by making it more more evident to students by making it more explicit.explicit.

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

Uncovering ChemistryUncovering 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’

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 Gradually Increasing Complexity

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

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 ArisesModels 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

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

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

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

Energy - Early and OftenEnergy - Early and Often

Reconnect Eth and EchReconnect 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

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

How to Teach it?How to Teach it?

constructivist vs transmissionistconstructivist vs transmissionist

cooperative inquiry vs lecture/demonstrationcooperative inquiry vs lecture/demonstration

student-centered vs teacher-centeredstudent-centered vs teacher-centered

active engagement vs passive reception active engagement vs passive reception

student activity vs teacher demonstrationstudent activity vs teacher demonstration

student articulation vs teacher presentationstudent articulation vs teacher presentation

lab-based vs textbook-basedlab-based vs textbook-based

Be the “Guide on the Side”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

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 WhiteboardPreparing the Whiteboard

Making PresentationMaking Presentation

NGSS PracticesNGSS Practices

Practice 1: Asking Questions and Defining Problems

Practice 1: Asking Questions and Defining Problems

What Teachers Do? What Students Do?

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Practice 2: Developing and Using Models Practice 2: Developing and Using Models

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Practice 3: Planning and Carrying Out Investigations

Practice 3: Planning and Carrying Out Investigations

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Practice 4: Analyzing and Interpreting DataPractice 4: Analyzing and Interpreting Data

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Practice 5: Using Mathematics and Computational Thinking

Practice 5: Using Mathematics and Computational Thinking

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Practice 6: Constructing Explanations & Designing Solutions

Practice 6: Constructing Explanations & Designing Solutions

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Practice 7: Engaging in Argument from Evidence Practice 7: Engaging in Argument from Evidence

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Practice 8: Obtaining, Evaluating, and Communicating Information

Practice 8: Obtaining, Evaluating, and Communicating Information

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What Could It Look Like???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

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Practices of the NGSSPractices of the NGSS

I noticed…I noticed… I wonder…I wonder…

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How Important Is Energy?How Important Is Energy?

Topics/Content Topics/Content Skills Skills

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A Coherent Approach to Energy

Larry DukerichLarry Dukerich

Dobson HS/Arizona State UDobson HS/Arizona State U

Gregg SwackhamerGregg Swackhamer

Glenbrook North HS, Northbrook, ILGlenbrook North HS, Northbrook, IL

Presentation at the Summer 2003 AAPT Meeting

Current State of Energy Concept

• Energy is regarded as an abstract quantity, Energy is regarded as an abstract quantity, ““inventedinvented”” for doing calculations for doing calculations

• Treatment of energy is inconsistent from discipline Treatment of energy is inconsistent from discipline to disciplineto discipline

• Students cannot use energy to adequately describe Students cannot use energy to adequately describe or explain everyday phenomenaor explain everyday phenomena

• Students are taught that energy comes in different Students are taught that energy comes in different formsforms

The Problem with Transforming Energy

• Focus on Focus on ““changing one form of energy into anothechanging one form of energy into anotherr””11 implies that there are different implies that there are different ““kindskinds”” of energy of energy

• ““Forms of energyForms of energy”” locution implies that somehow locution implies that somehow energyenergy is changing - diverting attention from the is changing - diverting attention from the changes in matter that we changes in matter that we cancan describe describe– James Clerk Maxwell argued against James Clerk Maxwell argued against ““forms of energyforms of energy””

treatment, calling it the treatment, calling it the ““old theoryold theory””

1- American Association for the Advancement of Science, Project 2061 Benchmarks Online,

Substance Metaphor

• Substance metaphor focuses attention on energy Substance metaphor focuses attention on energy storage and transferstorage and transfer– ““Energy is stored in different systems and in different ways in Energy is stored in different systems and in different ways in

those systems, and it is transferred by some mechanism or other those systems, and it is transferred by some mechanism or other from one system to anotherfrom one system to another””22

• Consider informationConsider information– ““ It would be nonsense to say that hard disk information is It would be nonsense to say that hard disk information is

transformed into wire information and then into RAM information transformed into wire information and then into RAM information and then into CD informationand then into CD information””33

• Use of substance metaphor can integrate the way Use of substance metaphor can integrate the way physics and chemistry approach energyphysics and chemistry approach energy

2, 3 - G Swackhamer, “Understanding Energy-Insights”

Problems with Energy in Chemistry

• Heat regarded as an entity, rather than a Heat regarded as an entity, rather than a mechanism for energy transfermechanism for energy transfer

• Different variables used interchangeablyDifferent variables used interchangeably

– Q - what you can calculateQ - what you can calculate

– E - what youE - what you’’d really like to discussd really like to discuss

– ∆∆H - what you H - what you cancan discuss discuss

• Only in college texts is treatment of 1st law of Only in college texts is treatment of 1st law of Thermodynamics more thoroughThermodynamics more thorough


• Tenuous connection between kinetic energy and Tenuous connection between kinetic energy and potential energy - typical examples are from realm potential energy - typical examples are from realm of physicsof physics

• Students try to apply energy conservation to Students try to apply energy conservation to heating or cooling curvesheating or cooling curves– Kinetic energy changes with temperatureKinetic energy changes with temperature

– Potential energy changes on plateausPotential energy changes on plateaus

– Therefore, energy is shuttling back and forth between kinetic and Therefore, energy is shuttling back and forth between kinetic and potentialpotential


• Role of energy in bonding is muddledRole of energy in bonding is muddled– Rearranging atoms in molecules results in energy changeRearranging atoms in molecules results in energy change

– But is it kinetic, potential or both?But is it kinetic, potential or both?

• Students conclude that somehow bonds store Students conclude that somehow bonds store energyenergy– ATP ADP releases energy because ATP ADP releases energy because ““high-energy high-energy

phosphate bondphosphate bond”” is broken is broken

– View is inconsistent with bond dissociation energyView is inconsistent with bond dissociation energy

Applying the Substance Metaphor

• Do brief coherent treatment of 1st Law of Do brief coherent treatment of 1st Law of Thermodynamics - Modeling Instruction in HS Thermodynamics - Modeling Instruction in HS PhysicsPhysics

• Focus on ways to represent energy storage and Focus on ways to represent energy storage and transfertransfer

Distinguish between attractions and chemical bonds

• Both involve electrostatic interactionsBoth involve electrostatic interactions

• Specificity and directionality of these interactions differ Specificity and directionality of these interactions differ sufficiently that it is useful to treat them separatelysufficiently that it is useful to treat them separately

• These interactions are associated with different kinds These interactions are associated with different kinds of changeof change

– Attractions - physical changesAttractions - physical changes

– Bonds - chemical changes Bonds - chemical changes

Two Categories of Potential Energy

• In physics, it is useful to subdivide potential energy In physics, it is useful to subdivide potential energy into gravitational, elastic and electrical categoriesinto gravitational, elastic and electrical categories

• In chemistry, it is useful to consider two categoriesIn chemistry, it is useful to consider two categories

– Interaction - due to van der Waals type attractions Interaction - due to van der Waals type attractions betweenbetween particles (non-directional & non-specific) particles (non-directional & non-specific)

– Chemical - due to bonds Chemical - due to bonds withinwithin molecules (covalent) or molecules (covalent) or withinwithin crystal lattices (ionic). Bonds are directional and crystal lattices (ionic). Bonds are directional and involve specific particles.involve specific particles.

Attractions and Energy

• Attractions Attractions lowerlower the potential energy of a system of the potential energy of a system of particles, whether due toparticles, whether due to

– gravitational forces between macroscopic bodiesgravitational forces between macroscopic bodies

– electrostatic forces between microscopic particleselectrostatic forces between microscopic particles

• It always requires energy to separate bound It always requires energy to separate bound particlesparticles

Incomplete Representation of Ech

• Standard chemical potential energy diagram (left) Standard chemical potential energy diagram (left) shows only part of the picture shows only part of the picture

Re-scale the Potential Energy Graph

• As we do in physics, we can represent energy As we do in physics, we can represent energy wells (-) as energy bars (+) by moving zero position. wells (-) as energy bars (+) by moving zero position.

Reconnect Ek and Ech

• Particles in system exchange EParticles in system exchange Ekk for E for Echch to rearrange atoms to rearrange atoms

181 kJ + N181 kJ + N22 + O + O22 ––> 2 NO ––> 2 NO

– Representation consistent with fact that an endothermic Representation consistent with fact that an endothermic reaction absorbs energy, yet the system coolsreaction absorbs energy, yet the system cools

Reconnect Ek and Ech

• Whether final kinetic energy of system is greater or Whether final kinetic energy of system is greater or lower depends on difference of chemical potential lower depends on difference of chemical potential energy of reactants and productsenergy of reactants and products

– Here, an exothermic reaction is depicted Here, an exothermic reaction is depicted

We Need to Keep Track of All of the Accounts During Change

• This treatment of energy storage and transfer is consistent This treatment of energy storage and transfer is consistent with that used in physicswith that used in physics– A ball is dropped from rest…A ball is dropped from rest…

• The story would not make sense if we considered only EThe story would not make sense if we considered only Egg

Extend This Treatment to Physical Change

• What happens during phase change?What happens during phase change?

– The substance doesnThe substance doesn’’t change - only the arrangement of t change - only the arrangement of the constituent particlesthe constituent particles

– We are considering the attractions We are considering the attractions betweenbetween molecules, not molecules, not the attractions between atoms the attractions between atoms withinwithin the molecules the molecules

– Use separate account - EUse separate account - Eii, the energy due to interactions, the energy due to interactions

Attractions Lower Energy of a System of Particles

• The more tightly bound the particles, the lower the The more tightly bound the particles, the lower the energy of a systemenergy of a system

– Particles in the solid state adopt the most orderly, lowest Particles in the solid state adopt the most orderly, lowest energy configurationenergy configuration

– Energy is required to break down this orderly array (melt Energy is required to break down this orderly array (melt the solid) the solid)

– Energy is released when particles in a liquid crystallize Energy is released when particles in a liquid crystallize into an orderly array (freeze).into an orderly array (freeze).

How is the Energy Stored?

• What are you getting for your energy dollar?What are you getting for your energy dollar?

– What is the added energy doing if the temperature of the What is the added energy doing if the temperature of the system is not increasing?system is not increasing?

– It must be overcoming It must be overcoming attractions between theattractions between theparticlesparticles

– The particles are lessThe particles are lesstightly bound in liquid phasetightly bound in liquid phase

– Interaction energy stored is related to ∆HInteraction energy stored is related to ∆H ff and mass of and mass of

systemsystem

During evaporation

• Particles in the liquid require energy input in order Particles in the liquid require energy input in order to overcome attractions and become widely to overcome attractions and become widely separated in the gas phase.separated in the gas phase.

• Unless energy is supplied to the system, energy for Unless energy is supplied to the system, energy for this change must come from another account, Ethis change must come from another account, Ekk

• Particles in remaining liquid become cooler Particles in remaining liquid become cooler (lower E(lower Ekk))

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Keeping Track of Energy During Chemical ChangeKeeping Track of Energy During Chemical Change

A coherent way to treat energy in chemical reactions

A coherent way to treat energy in chemical reactions

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The Conventional Approach

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

• 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

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Modeling ApproachModeling 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

• 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

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Endothermic reactionEndothermic 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 energyenergy + 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

• 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 energyenergy + 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

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Endothermic reactionEndothermic reaction• This is the standard energy diagram

found in most texts.

• But it doesn’t tell the whole story.

• This is the standard energy diagram found in most texts.

• But it doesn’t tell the whole story.

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Energy Bar ChartsEnergy Bar Charts• Show energy transfers between

surroundings and system• Allow you to consider other energy

accounts

• Show energy transfers between surroundings and system

• Allow you to consider other energy accounts

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Consider role of Eth 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

• 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

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Heating system increases Eth

Heating system increases Eth• Hotter, faster molecules (surroundings)

transfer energy to colder, slower molecules (system)

• Now reactant molecules are sufficiently energetic to produce reaction

• Hotter, faster molecules (surroundings) transfer energy to colder, slower molecules (system)

• Now reactant molecules are sufficiently energetic to produce reaction

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Now reaction proceedsNow reaction proceeds• During collisions, particles trade Eth

for Ech as products are formed

• After rearrangement, resulting particles move more slowly (lower Eth).

• During collisions, particles trade Eth for Ech as products are formed

• After rearrangement, resulting particles move more slowly (lower Eth).

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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

1.Heating system increases Eth of reactant molecules

2.Energy is transferred from Eth to Ech now stored in new arrangement of atoms

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Exothermic reactionExothermic 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

• 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

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Exothermic reactionExothermic 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.

• 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.

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Exothermic reactionExothermic 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

• Now take into account changes in Eth • When reactant molecules collide to produce

products that store less energy, new molecules move away more rapidly

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Exothermic reactionExothermic reaction• System is now hotter than surroundings;

energy flows out of system until thermal equilibrium is re-established

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

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1. Decrease in Ech results in increased Eth

2. System is now hotter than surroundings3. Energy eventually moves from system

to surroundings via heating

1. Decrease in Ech results in increased Eth

2. System is now hotter than surroundings3. Energy eventually moves from system

to surroundings via heating

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Contrast Conventional Diagram

Contrast Conventional Diagram


• But, again,it doesn’t tell much of the story.


• But, again,it doesn’t tell much of the story.

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But what about energy used to start reaction?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.

• 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.

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What about a spontaneous endothermic process?

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

• 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

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Reaction useful for cold-packs

Reaction useful for cold-packs

• The system trades Eth for Ech

• Eventually energy enters cooler system from warmer surroundings (you!)

• The system trades Eth for Ech

• Eventually energy enters cooler system from warmer surroundings (you!)

Education

NGSS Chemistry Webinar