NGSS Chemistry Webinar

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

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  • We’re here to tell you about the application of the Modeling Method of instruction (first developed for use in high school physics) to the high school chemistry course.
  • First some background on what is the problem with conventional instruction.
    Bullet-1
    David Hestenes refers to the first as “factons”, what students record and try to reproduce on tests. The 2nd category he calls “factinos”, stuff that passes unimpeded through students’ heads.
  • Our students don't share our background, so key words, which conjure up complex relationships between diagrams, strategies, mathematical models mean little to them. To us, the phrase inclined plane conjures up a complex set of pictures, diagrams, and problem-solving strategies. To the students, it's a board, and it makes a difference which way it is tilted.
    All my careful solutions of problems at the board simply made ME a better problem-solver.
  • There is a big difference between the mathematical ‘game’ of stoichiometry and being able to describe what is going on in a reaction vessel. Ideally, students would do both simultaneously.
  • What does it mean to be ‘2 parts hydrogen and 1 part oxygen’? There can be a very real gap between their words and how they perceive matter at the microscopic level (for more than just water!!)
  • The real roadblock to many students is not which atomic model they use, but whether they have ANY sufficiently developed atomic model that is consistently applied.
    Kids today whiteboarded predictions of what would happen when iron and sulfur formed a compound. Every student (honors chemistry) showed that the individual particles of Fe and S disappeared and some new particle appeared. (blue & yellow gave rise to green, not blue-yellow) – though this was a launching activity to gauge students’ prior knowledge and preconceptions, before teaching activities commenced, it pointed out how “having learned” about compounds in other science classes didn’t mean they understood them.
    SAMPLE STUDENT WORK NEXT
  • The steel wool turns color when heated. Some think that some part of the gas from the burner flame in now trapped in the wool, but few actually drew atoms that combined to form new substances.
  • This is why I have a problem with texts that ruin the story by going to the end of the book right away. If we want students to see science as more than a collection of facts, then we have to connect our models to the evidence that lead to them.
  • What should we teach?
    Our students should learn to do the following:
    They should see that physics involves learning to use a small set of models, rather than mastering an endless string of seemingly unrelated topics.
  • This word is used in many ways.
    The physical system is objective; i.e., open to inspection by everyone. Each one of us attempts to make sense of it through the use of metaphors. Unfortunately, there is no way to peek into another’s mind to view their physical intuition. Instead, we are forced to make external symbolic representations; we can reach consensus on the way to do this, and judge the fidelity of one’s mental picture by the kinds of representations they make.
    So the structure of a model is distributed over these various representations; later we’ll provide some specific examples.
  • Students WILL work from a model of matter** - the question is which model and is it
    a rigorous, scientifically supported model
    applied consistently to all situations
    **refer to storyboards
  • Emphasis on points 1 and 2.
  • Reference: “The Story So Far” doc
  • Reference: Energy Paper
  • Here are the key ways in which the modeling method differs from conventional instruction.
    Students present solutions to problems which they have to defend, rather than listen to clear presentations from the instructor. The instructor, by paying attention to student’s reasoning, can judge the level of student understanding.
  • This talk followed Gregg Swackhamer’s talk at the AAPT meeting in Madison, WI in the Summer of 2003. You can find his talk by pointing your browser to http://modeling.asu.edu/modeling/00Madison.ppt
  • Gregg’s talk gave specific examples of student difficulties in these areas.
  • It’s difficult to develop a coherent approach to energy when there’s no consistency in the language used to describe it.
  • Gregg’s paper: Cognitive Resources for Understanding Energy <http://modeling.asu.edu/modeling/CognitiveResources_Energy.pdf> explains the use of the substance metaphor to describe energy.
  • Just as physics folks treat Work as a thing, rather than as a process by which energy is moved between system and surroundings, chemists talk about Heat as if it is something different from energy. You will even find people saying that an object can store heat.
  • When authors of chemistry texts try to give students a sense of the difference between potential energy and kinetic energy, they use examples like a skier. At the top of a hill, he has potential energy. As he goes down the hill and his speed increases, this energy is converted into kinetic energy. Chemistry students are left wondering where is “the hill” in a system of molecules?
    The idea student have drilled into them is that energy is always conserved. So, they inappropriately invoke this principle during a melting even though they are constantly adding energy to the system.
  • We must learn to avoid using language like “bonds store energy”. Chemical bonds are representations of low-energy configurations of atoms. It always takes energy to pull bound particles apart. Energy is released when atoms become bound. In the case of the hydrolysis of ATP, a small amount of energy is required to break a P - O bond when a phosphate is removed from ATP; but a greater amount of energy is released when the PO3– combines with H2O to form H2PO4– ion.
  • The Modeling Instruction in High School Physics curriculum in mechanics has a unit that does a thorough treatment of energy storage and transfer.
  • One of the big problems in chemistry is that our systems involve collections of particles that are bound in different ways; in order to adequately describe change, it is useful to distinguish attractions from bonds.
  • The potential energy of a system depends on the configuration of the constituent particles of a system. Just as we find it useful to have sub-categories of potential energy in physics, depending on the phenomena we are trying to describe, it is also useful to do the same in chemistry.
  • This is a key point to keep in mind, whether you are trying to describe solids, liquids and gases, (energy due to interactions) or the chemical change (chemical potential energy).
  • In any chemistry text, you see only a part of the picture (left). You never see where the zero energy position is. You might see this when there’s a discussion of the potential energy well when two atoms combine to form a bond, but not when a system of molecules are rearranged to form new molecules.
  • In van Heuelen energy bar charts, the zero position for gravitational potential energy is moved from where the two bodies are infinitely far apart to when the two bodies are touching. In this way, we are comparing positive energy quantities instead of negative ones. In chemical reactions, it is not necessary to separate all the atoms completely in order to form products, but the reactants do adopt a higher energy configuration (activated complex) before they can go on to form products.
  • The chemistry texts don’t really connect kinetic and chemical energy until they treat kinetics. Until then students are left wondering where the energy required to rearrange atoms in a reaction comes from. In the case above, if the arrangement of the particles in the products stores more energy then the arrangement in the reactants, then the energy required to produce this change must come from some other account - the kinetic energy of the particles.
  • In an exothermic reaction, the products store less energy than do the reactants; the excess energy is moved to the kinetic energy account and the system becomes hotter. Eventually, the system loses energy to the surroundings via heating as the system and surroundings reach thermal equilibrium.
  • If we did not consider kinetic energy in physics examples, the behavior of a falling object would make no sense.
  • Although few chemistry texts explicitly discuss energy storage during physical change, the same principles apply.
  • The naïve tendency is to relate strong attractions to high interaction energy. When particles have no interactions, their potential energy is zero. The stronger the interactions, the deeper they fall into a potential energy well. Keep in mind that we are relocating the zero point for the potential energy due to interactions so that we don’t have to compare (-) values.
  • When a solid substance reaches the melting point and the temperature remains constant, the energy supplied to the system is not stored as Ek. We account for it by by using the Ei account.
  • When a liquid evaporates at a temperature lower than its boiling point, the energy required to separate the particles must come from the Ek account. When the system cools, energy is transferred from the surroundings to the system.
  • NGSS Chemistry Webinar

    1. 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. 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. 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. 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. 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. 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. 7. Representation of Matter  Question: “What’s happening at the simplest level of matter?”
    8. 8. More Storyboards Gas Diffusion: Where ’s The Air? Aqueous Diffusion: The Continuous Model of Matter
    9. 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. 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. 11. What Do We Mean by Model? Models are representations of structure in a physical system or process
    12. 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. 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. 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. 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. 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. 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. 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. 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. 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. 21. Preparing the Whiteboard
    22. 22. Making Presentation
    23. 23. NGSS Practices
    24. 24. Practice 1: Asking Questions and Defining Problems What Teachers Do? What Students Do? 24
    25. 25. Practice 2: Developing and Using Models What Teachers Do? What Students Do? 25
    26. 26. Practice 3: Planning and Carrying Out Investigations What Teachers Do? What Students Do? 26
    27. 27. Practice 4: Analyzing and Interpreting Data What Teachers Do? What Students Do? 27
    28. 28. Practice 5: Using Mathematics and Computational Thinking What Teachers Do? What Students Do? 28
    29. 29. Practice 6: Constructing Explanations & Designing Solutions What Teachers Do? What Students Do? 29
    30. 30. Practice 7: Engaging in Argument from Evidence What Teachers Do? What Students Do? 30
    31. 31. Practice 8: Obtaining, Evaluating, and Communicating Information What Teachers Do? What Students Do? 31
    32. 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. 33. Practices of the NGSS I noticed… I wonder… 33
    34. 34. How Important Is Energy?  Topics/Content  Skills 34
    35. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 55. Keeping Track of Energy During Chemical Change A coherent way to treat energy in chemical reactions 55
    56. 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. 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. 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. 59. Endothermic reaction • This is the standard energy diagram found in most texts. • But it doesn’t tell the whole story. 59
    60. 60. Energy Bar Charts • Show energy transfers between surroundings and system • Allow you to consider other energy accounts 60
    61. 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. 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. 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. 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. 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. 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. 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. 68. Exothermic reaction • System is now hotter than surroundings; energy flows out of system until thermal equilibrium is re-established 68
    69. 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. 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. 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. 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. 73. Reaction useful for cold-packs • The system trades Eth for Ech • Eventually energy enters cooler system from warmer surroundings (you!) 73

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