Designing a Unit in Science

Part 1: What do we want in a science unit?

I have been asked a few times how I design my units and lessons for science. The first time I was asked, I was really not sure and found it challenging to explain. Right now I am starting to design a new chemistry unit for grade 10 science, so I thought this might be a good opportunity to examine my work process and figure out what I'm doing! A bonus is that this is a unit that is outside of my comfort zone: I am a physicist who last studied chemistry in high school! Yikes!

I find the beginning of the design process to be the most challenging: to understand the learning goals and the general strategies we will use to meet them. As many of us do, I start with the curriculum documents.

Examine the curriculum. Read over the curriculum documents for the grade 10 chemistry unit. Then read the document for the grade 9 chemistry unit and the related grade 11 chemistry units. This gives a sense of the raw content to cover as well as the relationships between past and future learning.

This is only modestly helpful! I personally feel a sense of unease because the curriculum documents fail to present a clear narrative thread that makes sense from a scientific perspective, as opposed the taxonomical perspective that many educators and bureaucrats take. A traditional approach that is often codified in textbooks is to break up scientific knowledge into well defined units, break up those units into topics, and present those topics in a sequence that makes logical sense to those who already have the big picture. This approach tends to be exhaustive, in the sense of presenting all the discrete pieces of knowledge that fall under each topic, rather than inquisitive. It is an approach that makes sense to teachers but hides the science: the approach does not reflect how scientists work and think. So, I will try a different approach:

Think like a scientist. Why is anybody interested in these topics? How were the ideas first developed? What were the landmark historical experiments that allowed people to figure out this stuff? What evidence did they see that led to the development of these ideas? And how do contemporary practicing scientists use these ideas?

This is how I try to find the narrative thread that draws the ideas of the unit together and makes sense from the perspective of somebody using the process of science to explore the world. A quick reminder about science is helpful: it is usually instigated by someone making a surprising or puzzling observation and realizing they don’t know what is going on!

Find the scientific narrative. Develop a sequence of explorations, preferably based on observations that can be made in the classroom, that leads students through the development of the unit’s scientific ideas. One long arc is preferable but is often not possible. There may be a few different starting points that are needed in order to cover the unit’s main ideas.

There should be a sequence of reasoning that leads from observation, to idea, to new observations, and so on, forming a scientifically informed narrative arc for the unit of study. This approach helps bring a strong conceptual unity to the ideas that are covered, since they build on one another as our understanding deepens and as we use newfound tools to tackle more disparate and complex phenomena. This doesn't have to follow or mimic a particular historical sequence of discovery; often the actual history is very messy and complex. However, our students are discovering these ideas for the first time, so the sequence of exploration needs to make sense to them as they build, explore, and test the ideas. This can be quite challenging given the jumble of ideas that are often presented in curriculum documents; these documents are seldom designed by experts in both science and learning!

Focus on what is important. Identify the most important ideas in the unit and the supporting ideas that lead to it and from it. Pretty much everything else should be eliminated from the unit.

Content from the curriculum documents often needs to be removed. It takes time to develop a scientific understanding through inquiry; we must cover less content to allow students to build a deeper understanding. We need to do a cost benefit analysis for the effort that is put into learning a new idea. If that idea is rarely used within the unit of study, then it is probably not worth learning. My favorite example that makes my head spin every time I see it comes from the grade 9 curriculum document for the chemistry unit where it mentions the idea of viscosity (page 52, C2.1). Really? This is totally bizarre and an all too common example of the taxonomical approach: the idea of viscosity falls into the category of “physical properties” but is of extraordinarily little use in the unit and is presented with little or no physical motivation or exploration (Why are liquids viscous? That's not for grade 9's to explore!) So, sometimes a lot of work is needed to find the truly important ideas and skim off the dross. This is what a curriculum document should do for us, but here we are.

Authentic skills and meaningful tasks. The skills students develop in the unit should model skills or thought processes used by practitioners. This will help to determine the major tasks that we incorporate in the unit. The more authentic the tasks are, the more intrinsically motivating they will be for our students. Practitioners also work in teams, so group work and collaboration are essential elements of the unit design. The majority of student time should be devoted to meaningful tasks as opposed to the sharing of information (direct instruction).

How do people outside of high schools use science ideas? There are a lot of curious practices that take place in high school classrooms that bear no resemblance to the way people use scientific knowledge in the wider world. Some of these might be pedagogically useful but others are likely just crutches that teachers lean upon to manage a disjoint and unscientific curriculum - or they mimic the ways in which the teacher was taught. Outside of high school, people use scientific knowledge to: explain things (understand what has happened), make predictions (describe the future), test ideas (check their understanding), or build or do useful things (change the future). Our students should spend most of their learning time doing these things.

Learning is about connections. Learning will be deeper and more useful when many connections are made between new content and content elsewhere in the course, in past study, or from students’ experiences. Routinely draw connections whenever possible, especially amongst the most recently learned ideas and the key ideas of the course. If an idea is actually useful for high school study, it should be connected to many other ideas in the unit and beyond.

We want to avoid introducing an idea or skill, briefly using it, and then dropping it for the rest of a unit. Students’ understanding, especially of complex concepts, will become much deeper when they regularly use new skills or ideas in a variety of situations throughout the unit and hopefully across the entire course. This suggests approaching each task more thoughtfully and drawing more connections with each experiment or demonstration. If the students have the ability to draw a lot of ideas out of a situation, they should regularly practice this. There is a risk of this becoming tedious, but if it is done well, even a simple experiment or demonstration becomes very rich and encourages engagement and a deeper understanding.

Context is everything. When an idea is introduced, make sure it is used immediately. Don't introduce ideas well in advance, thinking they will be useful a week or two later. Don't review skills that aren't immediately applied. Learning is contextual and time sensitive: unless ideas are immediately useful and then regularly reinforced, they will be soon forgotten. It is not necessary to cover all of a topic at once: cover the parts that will be used and return to the topic later when other parts are needed.

The instinct to be exhaustive is a powerful one amongst teachers. Resist the urge! What is most useful for students is what is relevant to the task at hand. A major problem is that often there is no task: the learning is being done in a scientific vacuum; no greater question is being answered, no problem is being solved. Make sure what you teach them is targeted to an immediate task, even “boring stuff” like the rules for naming compounds.

This outlines the general thinking that I use when I design a science unit or lesson. As I work through this process and develop the grade 10 chemistry unit, I will provide further updates. I hope you have found this discussion interesting or helpful! Stay tuned for more!

Part 2: Generating Ideas for Learning Experiences

Searching for the atoms

In the last article I wrote, I described the general ideas I used to think about and design science unit. Now comes the hard part: finding the basic atoms or the core ideas to build the unit from. For most other units, I have a fair bit of experience with the topics, giving me a good sense of their importance, the connections between them, and a good learning progression. With grade 10 chemistry, this is not the case! I don't think I've taught these ideas before, so I don't have much experience to fall back on. I do know, however, what I don't want. I don't want a lesson sequence that goes: welcome to chemistry, naming rules, bonding, polyatomic ions, types of reactions. These topics are typically presented as a sequence of new skills, but without much context or rationale for learning and without much science! Coming up with an alternative to this is not easy for me, so I start collecting ideas:

Atoms of Learning Form Molecules

Some of the ideas start to stick together and form molecules! A few themes start to emerge (i.e. precipitate out of the solution!):

Evidence. Provide experimental evidence for the existence of the products of a reaction (i.e. How did people originally figure out what results from a reaction?)
Models. Connect new learning with particle models (a picture of shapes that represent the bulk atoms in a substance) and the kinetic molecular theory. This will help us develop a clear microscopic, physical model for the reactions we will be studying. This is the missing science mentioned above. In fact, the curriculum document has very little science in the 10 chemistry unit, so this needs to be supplemented or else students will have no idea what the new skills are actually describing.
Skills. Introduce the new skills (Lewis diagrams, naming compounds, balancing equations, etc.) in incremental steps as they are needed by some context, rather than in one exhaustive lesson. This is the pedagogical technique of spiralling.

Find the key learning experiences

My next step is to take these “molecules of learning” and form the key experiences students will have in the unit. At the moment I have five: an exploration of the electrolysis of water, dissolving zinc in an acid, figuring out what a solution is, burning magnesium, and a double displacement reaction. Below you can see the rough notes I've put together for these experiences, which will likely become lessons. Note that I haven't yet figured out what order would be appropriate or how to sequence the building of new skills. They are just rough ideas!

(1) What’s going on in a solution?

Test properties of solutions of salt and of sugar.

Evidence for dissociation into ions? Conductivity measurements.

Testing experiment: is dissolving a chemical change or a physical change?

Dissolve solute and boil solution until water is gone, compare mass before and after.

Draw a particle diagrams for water, solute, and solution for both salt and sugar.

How does temperature affect the results? Draw connections with kinetic molecular theory.

Review valence and ionic bonding as part of this investigation.

Introduce Lewis diagrams as part of this investigation?

Possibly explore movement of ions within solution to show how the electric current or circuit is completed?

(2) Single displacement reaction investigation: Zinc and hydrochloric acid

Predict possible products.

Draw particle diagrams for zinc and hydrochloric acid solution

Initial experiment: add hydrochloric acid to zinc, observe the reaction. There's a mystery to solve!

Testing experiments: generate ideas to test what products are present, look up properties of possible products

capture the gas, burning splint test
zinc and water: is there A noticeable reaction here?
is zinc combining with chlorine? Add small amounts of hydrochloric acid until the zinc is fully reacted. Heat solution until water is boiled away. Compare mass of initial zinc with residue. What are physical properties of zinc chloride? Look up. How many chlorine atoms combine with each zinc atom? (Hopefully the mass of the residue is roughly double that of the original zinc)

Draw particle diagrams for confirmed products.

Draw Lewis diagrams illustrating reaction. Figure out the valance of Zinc!

Label type of reaction.

(3) Decomposition reaction: Electrolysis experiment

Initial experiment: turn on current, observe what happens using simple apparatus (plastic cup, thumb tacks, 9V battery, no gas collection tubes yet!).

Draw a particle diagram for water sample.

Is this a chemical or physical change? What tests could we perform?

Testing experiments:

measure temperature near source of bubbles
collect gas. Cool down gas and look for condensation. New observation: observe volumes of gas. This must be explained.
collect gas. Perform gas tests to identify.

Draw particle diagrams for samples of products.

Draw a particle diagram for reaction: challenge to get the number of molecules correct. Explain gas volume observations.

Introduce idea of balancing equations for reactions.

Draw Lewis diagrams.

Label the type of reaction.

As a variation: add salt or baking soda to the reaction. How does this affect the chemical reaction?

(4) Synthesis reaction: burning magnesium

burn magnesium, collect ash, make mass measurements

determine what the magnesium is reacting with: what component of the atmosphere?

(5) Double displacement reaction: lead nitrate and potassium iodide

Pb(NO3)2 + 2KI --> PbI2 + 2KNO3

Note that no gases are produced! This is evidence that then nitrogen and oxygen remain bonded. This motivates the idea of a polyatomic ion.

Playing with chemicals!

Now that I have some ideas to work with, it's time to start playing with chemicals. I am not familiar with some of these reactions and so I need to spend some time trying them out and figuring out how to implement them to accomplish the different goals of the lessons. Based on my thoughts so far, one reaction like the zinc with hydrochloric acid might need to be done three different ways in order to emphasize or allow different observations and measurements. This experimenting will take some time so, please stay tuned for future updates as my unit planning develops!

Part 3: Designing a Progression of Concepts and Skills

The Search for Science

Many units in the Ontario science curriculum are overflowing with expectations that need to be sifted through and weeded out, but this is not the case with the grade 10 chemistry unit! I was a bit surprised at the small number of expectations and especially surprised with the small amount of science! Imagine that for a science curriculum. The unit mentions a lot of skills such as naming compounds and balancing equations but has very little to say about what students should understand of chemical processes (conservation of mass is the only piece of understanding mentioned). A younger colleague of mine recounted his own experience as a student learning grade 10 chemistry: he found it just like a French class, practising grammar and conjugating verbs. This is a common pitfall in science education: reducing the learning of science to an academic exercise of manipulating information without much connection to the underlying physical world. As I put together the key learning experiences for my chemistry unit (described in part two of this article), I was searching for the science: the key pieces of understanding of our physical world that students need to make sense of chemical reactions.

Particles and Energy

There are few ideas more helpful for understanding our world than the particle model of matter and the flow of energy. These ideas have tremendous explanatory power and are essential for creating useful conceptual models of wide-ranging physical phenomena across all grade levels. It is a serious weakness of the current Ontario secondary science curriculum that these ideas, and energy especially, are not explicitly involved in almost every strand and grade level. (The American Next Generation Science Standards from 2013 does not have this weakness - I am not optimistic about our upcoming revised science curriculum.) The topic of energy needs to be treated in a fulsome way in the junior science courses before the sciences split off in grade 11. In particular, the concept of bond energy is particularly fraught and students in senior biology can end up discussing ATP with no conceptual foundation for energy in chemical processes. This results in the incorrect understanding that chemical energy is stored “in a bond”. Including a focus on energy will be challenging because it is both subtle and is not an explicit curriculum expectation. Adding energy can’t be allowed to overburden the unit, otherwise it won't help out students and teachers won't use the lessons. Energy needs to be treated in a simple and conceptually clear way while still having useful explanatory power.

Pictures of Chemistry

Because of their value, I am choosing to emphasize particle and energy ideas throughout the grade 10 chemistry unit. The particle model will help students create pictures of chemical phenomena and energy concepts will bring them to life! This also activates our visual processing centres for learning, which are very powerful and often help struggling students. I want to make sure that when we discuss a chemical reaction, my students have a useful picture in their minds to work with. The emphasis on drawing particle pictures will force a lot of conceptual reconciliation and sensemaking: when we represent knowledge in multiple representations (pictures, words, equations) we are forced to draw connections between the representations and often discover many parts of our understanding that are incomplete or just plain wrong! Here is a sneak peak at what multiple representations might look like:

and

A “simple” picture like the one above showing Zn + HCl(aq) consolidates a lot of scientific understanding.

The skeleton event: a lesson run-through

In part two of this article, I listed five important learning experiences that will become future lessons. Since I haven't taught these topics, I don't have a good sense of the sequence in which to explore these, introduce chemistry skills, and build upon them. To work this out, I developed each learning experience into a skeleton lesson: a very simplistic outline of a sequence of work and thinking. I call this a skeleton lesson because it is missing a lot of detail; it doesn't explain any of the new ideas or skills and it doesn't review any of the prerequisite ones. Then I worked through each skeleton lesson and carefully monitored the ideas and skills that I used. Take a look at this example for the single displacement skeleton lesson.

Here I caught that I was balancing an equation and needed knowledge of ionic versus covalent compounds to draw the particle diagram for the solutions. Also, as a keen reader pointed out (thanks Lisa!), I need to carefully label the charge as 2+, etc. The skills I used were relatively simple, so this lesson could come early in the unit. I also realized that predicting the possible products of the reaction would be tough for students. This will require some careful scaffolding to help students come up with reasonable predictions. I will also need to scaffold their work with molecular mass and mass ratios very carefully: I don't want to introduce moles and do full-blown stoichiometry, but I do want them to use some proportional reasoning to make predictions about the mass of a reaction's products. Completing the skeleton lesson also gives me a sense that this learning experience will require two class periods to complete.

Who's on first?

It took me quite a while to figure out the sequence for the five learning experiences. This might seem quite obvious for an experienced chemistry teacher, but I found it quite challenging and went back and forth on many occasions. I now have a learning sequence with the addition of an energy lesson:

Review elements / bonding
Collisions and Energy
How do solutions behave?
Decomposition reaction
Synthesis reaction
Single Displacement Reaction
Double Displacement Reaction

Many of these will be two classes long. I am planning on treating acids and bases as part of the climate change unit! My next task is to tackle the lesson on energy. I need to do this first because it will establish the conceptual framework that I use through the rest of the unit. Stay tuned for the results!

Part 4: Laying the conceptual groundwork and creating the first lessons

In the previous sections of this chronicle, I put together a rough outline for a sequence of lessons and developed a few skeleton lessons based on the key learning experiences I identified for the chemistry unit. I also decided on a conceptual framework involving the concept of energy and particle pictures. This has provided quite a challenge! As I mentioned earlier, I am not a chemist and did not study chemistry in university. As a result, I have a lot of learning to do. When I decided to create a new grade 10 chemistry unit, I started cracking the books, so to speak, to help improve my content knowledge and explore the challenges of learning chemistry.

Time to start my learning

I was very fortunate to participate in a webinar last Monday with the author and presenter of the Veritasium YouTube channel, Derek Muller. He made a comment that reassured me in my science writing habits: He said that to explain something well, especially a topic that you are less familiar with, you need to delve two levels deeper than what you will be explaining. Now I don't feel so crazy! In preparing to write the introductory chemistry lessons, I read a lot of textbooks especially concerning physical chemistry. (I was pleased to discover some overlap with a few of my university physics courses here. Yay physics!) I also explored the educational literature to find out what pedagogical experts have to say about the challenges of learning energy in chemistry. Both avenues of reading were eye opening.

Creating pictures of chemistry

Every now and then, often as an aside, a textbook passage would describe in detail the physical happenings that I needed to create the particle pictures I am hoping for. But I noticed how rare such passages are: the focus of higher-level chemistry almost is almost always mathematical and seems to avoid conceptual pictures. An important part of bringing my particle diagrams to life will be simulations - I will be trying to stimulate as much as possible! I was lucky to find software that scientists and researchers use to model chemical processes on an atomic level, molecular dynamics software (this particular software is old, not user friendly, and runs on Java). Here is a video I made with this software:

Its very important for conceptual development that students have reliable, pictorial models of chemical processes; beakers of solutions shouldn't be black boxes! (A “black box” is any device or process that people use but do not understand the inner workings of. We provide some inputs, get some outputs, and don't really know what happens in between. This seems to me to be the way that chemical reactions are presented at the high school or even undergraduate level of study.) The pedagogical choice to emphasize particle pictures has required a surprising amount of background work!

The mess of energy in chemistry

It turns out that the topic of energy in chemistry is fraught with challenge! As I read more, I realized that I had to correct much of my own understanding. Back in my university days, I actually learned about Gibbs energy and Helmholtz energy; it turns out these are not just physics topics! But unfortunately, I didn't understand them at all. Not only that, I have discovered that I didn't really understand how energy is associated with bonding. There was an interesting mess of concepts in my head: my understanding of electrical potential energy from physics and an understanding of how energy is “stored” in bonds, especially “high-energy bonds” like those often discussed in biology. It's a bit embarrassing to say that it took me a while to sort this mess out, so I have a hunch that I might not be the only one to experience these difficulties.

Energy and bonding

Energy is worth taking a bit of time to discuss because it is a fundamental concept to chemistry and biology. Let's think about photosynthesis, which is a bit of a black box for me - I haven't seen this since high school! The inputs are sunlight, carbon dioxide, and water and the outputs oxygen and glucose. I have heard it described that the Sun’s energy is now stored in the bonds of the glucose molecule; I have a hunch this is how most students would describe it as well. The problem is, bonds don't store energy. At its most basic level, we need to add energy to a system in order to separate attracting particles, that is, to break bonds. When a bond forms, energy stored in the electrical interaction between attracting particles is transferred to the kinetic energy of the particles (in physics speak). Or, in the chemical vernacular, chemical energy transfers to thermal energy when a bond forms. Here is an analogy with gravitational energy that might be helpful. Suppose we have two jackets side by side, hanging from one hook. The two jackets will stay pretty close to one another, so we consider them to be bonded. Then we take one jacket, lift it up, and put it on a higher hook with another jacket. These two jackets are now very close so we consider them to be bonded. Energy was stored in the process of lifting up the jacket, but is not stored in the hook (the bond) - it’s just a hook! In this analogy, the energy is stored in the gravitational field and the hooks simply hold the jackets in their positions within that gravitational field. The conceptual challenge in relating the jacket analogy to an actual chemical system is that the gravitational field in the analogy represents an electrical field in the chemical system and the hooks in the analogy also represent electrical fields: everything is electrical! This makes pretty much any analogy challenging to unpack.

Chemical energy is a relative energy

When a bond breaks, the sundered particles could just return back together unless they get “hooked” to other particles (or escape to infinity). As the jacket analogy illustrates, there is no energy stored “in the bond”. A configuration of charged particles (particles bonded in a particular way) will have an amount of energy stored electrically relative to a different configuration of charged particles (particles bonded in a different way). When we refer to a “high-energy bond”, we need to be extra careful to make sure we do not leave the impression that the energy is stored in the bond (it is not). Instead, a “high-energy bond” consists of a collection of particles that have a lot of energy stored in the electric field due to their configuration relative to some other configuration. It would be better to say, “the particles are bonded in a high-energy state” rather than “the particles are in a high-energy bond”.

Describing energy in photosynthesis

None of this is simple, easy to describe, or conceptualize. But if we give students the wrong impression, as is often the case, they will believe incorrectly that a bond is high-energy because energy has been somehow “poured into” that bond. Returning to the photosynthesis example, the bonds found in water and carbon dioxide are strong, stable, and low energy (this configuration of hydrogen, oxygen, and carbon atoms have a smaller amount of energy stored electrically). The sun's energy is needed to break these strong bonds and create less stable bonds in glucose that “hook” the particles into a higher energy state relative to those of water and carbon dioxide (the configuration of glucose and oxygen has more energy stored electrically relative to the other configuration). The fact that the particles are hooked into a higher energy state means that there is a lot of energy that can transfer from the electric field, and do all sorts of cool stuff with ATP, before they return to the lower energy state in the configuration of water and carbon dioxide.

Climb out of the weeds and focus on grade 10

This whole discussion of energy, and the reading that helped me sort this out, is a good example of Derek Muller’s observation that we need to dive much deeper in order to reliably explain something at a simpler level. For the purposes of a grade 10 unit on chemistry, where energy is not even part of the curriculum, we must distill these energy concepts to their essence and find simple strategies for using them in meaningful ways.

The myth of single atoms

My experience teaching the grade 9 chemistry unit has encouraged in my mind some faulty understandings. In our introduction to the properties of elements according to the periodic table focuses on single atoms. When we look at ionic and covalent bonding, we imagine taking single atoms of different elements, combining them, and voila, a bond! In a conceptual model such as this, with no consideration of energy, bonding should always take place; a sodium atom should always bond with a chlorine atom. This impression isn't necessarily wrong, but it plants seeds for ideas that work against a more sophisticated understanding. A chemical reaction, or chemical change as is our focus in grade 9, doesn’t actually happen in the abstract and contextually empty way that I just described. The world we actually work with consists almost entirely of pre-bonded atoms! We really don’t find single sodium and chlorine atoms just kicking around, waiting for something to do. The way I introduce bonding in grade 9 does encourage this faulty impression. And the fact that we don't discuss metallic bonding leaves the atoms of many elements roaming free, despite being a solid chunk of metal! Furthermore, since pretty much all atoms start off bonded, a chemical reaction can only begin with an input of energy and the breaking of bonds, not the making of bonds. Perhaps … we should teach bond breaking before making!

Discovering the basic energy concepts of chemistry

My new grade 10 chemistry unit begins with a review of grade 9 ideas concerning the atom and elements of the periodic table. Then the second lesson gets right to the heart of energy in chemical processes (note that we haven't reviewed bonding yet!). We begin by observing the reaction of calcium in water, using a beaker of cold water and a beaker of hot water. Here is one of the videos that I created for this lesson:

It is our job as scientists to explain the differences that we observe! Our tools for doing this will be particle pictures and energy. What do we get when we combine particle pictures with energy? Collisions! Chemistry is all about the collisions between tiny, charged particles and the energy changes that result. The whole unit that I am designing will have a strong physical chemistry flavor because of this basic fact and our choice of tools. The questions we ask about the hot and cold water reactions will lead us to our core energy ideas.

Why is the reaction in the hot water faster?

In grade 9 we emphasize, wherever we can, the kinetic molecular theory. This helps students to connect the higher temperature of the water with faster moving water molecules, making collisions with the calcium more violent! The temperature comparison suggests that there must be a minimum speed or energy that water molecules must have in order to somehow cause the reaction. Why? Because the calcium atoms are bonded together (a very important fact)! Water molecules must collide with enough energy to break these bonds. So thermal energy is required to break bonds, which we can think of like the currency that atoms use to pay for reactions.

Why does the temperature of the system increase?

Further observations using temperature probes show suggest more energy ideas:

The temperature of the system (the left-hand measurement) is increasing while the breaker’s contents turn white and cloudy. A chemical change is taking place with a new compound forming. This requires the creation of new bonds and results in the thermal energy of the system increasing. Where did this energy come from? It was stored in the electrical interactions between the particles, which we will call chemical energy.

Electrical interactions and changes in energy

Those key observations of the calcium reaction help to define the basic energy concepts we will use in grade 10: reactions cause energy to transfer between chemical and thermal forms. We further illustrate this using marbles on a ramp that models a Lennard-Jones potential curve. This helps to visually illustrate the changes in kinetic energy (thermal energy) and electrical energy (chemical energy represented by gravitational energy in this model).

The Internal Energy

If we were to delve really deep into the particle processes at work during a chemical reaction, we might see a multiple steps, each involving the breaking and making of bonds and multiple transfers of energy. This is rather complex and we would like to avoid this entirely in grade 10. Luckily, if we step back from these details and focus on the chemical system as a whole, the energy picture becomes simpler. As a result of all the bond breaking and making, the thermal energy of the system either increases or decreases. If it increased, the chemical energy must have decreased; if the thermal energy decreased, the chemical energy must have increased. This allows us to define the internal energy of the system: a combination of its thermal and chemical energies (and an important steppingstone to enthalpy and Gibbs energy). We will describe these shifts within the internal energy using a simple statement: Eth -> Ech or Ech -> Eth.

The system and its environment

But wait a minute! Our beaker is not isolated from the rest of the world. As the reaction takes place, energy changes begin to occur outside the system, as shown on the right-hand thermometer in the previous temperature video. The glass of the beaker and the air surrounding it begin to warm up, providing evidence for a flow of energy from the system to the environment. This is our first example of an exothermic reaction. It's actually pretty cool that we can infer what is happening to the bonds of microscopic particles just by comparing two thermometers! We will illustrate this using energy flow diagrams:

A teaching experiment

This constitutes the conceptual framework that I will use in our grade 10 unit on chemistry. My hope is that this provides a conceptually deep, yet simple, way of understanding chemical reactions. But of course, I won't know for sure until I try teaching it! The materials I have created thus far are available on my website. Since I am not a chemistry expert, I would really appreciate any thoughts and suggestions that you might have. Feel free to explore the lessons in the word document but be sure to follow along with the downloaded PowerPoint so you can observe the videos.

Readings

Here is a list of some of the articles I read to help my understanding of chemical energy. They are all very interesting!

Cooper, Melanie M., and Michael W. Klymkowsky. "The trouble with chemical energy: why understanding bond energies requires an interdisciplinary systems approach." CBE—Life Sciences Education 12.2 (2013): 306-312. https://www.lifescied.org/doi/full/10.1187/cbe.12-10-0170

Cooper, Melanie M., and Ryan L. Stowe. "Chemistry education research—From personal empiricism to evidence, theory, and informed practice." Chemical reviews 118.12 (2018): 6053-6087. https://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.8b00020

Dhindsa, Harkirat S., and David F. Treagust. "Prospective pedagogy for teaching chemical bonding for smart and sustainable learning." Chemistry Education Research and Practice 15.4 (2014): 435-446. https://pubs.rsc.org/en/content/getauthorversionpdf/c4rp00059e

Dreyfus, Benjamin W., et al. "Chemical energy in an introductory physics course for the life sciences." American Journal of Physics 82.5 (2014): 403-411. https://arxiv.org/pdf/1308.3667

Dreyfus, Benjamin W., et al. "Ontological metaphors for negative energy in an interdisciplinary context." Physical Review Special Topics-Physics Education Research 10.2 (2014): 020108. https://link.aps.org/pdf/10.1103/PhysRevSTPER.10.020108

Stacy, Angelica M., et al. "Launching the space shuttle by making water: the chemist’s view of energy." Teaching and Learning of Energy in K–12 Education. Springer, Cham, 2014. 285-299. https://scholar.archive.org/work/n6zeenzdjzf4pkloj3c4djguyy/access/wayback/http://esummit-umb.net/sites/default/files/articles/files/Stacy%20Energy%20summit%20paper%20revised%202.pdf

Tsaparlis, Georgios, Eleni T. Pappa, and Bill Byers. "Proposed pedagogies for teaching and learning chemical bonding in secondary education." Chemistry Teacher International 2.1 (2020). https://www.degruyter.com/document/doi/10.1515/cti-2019-0002/html

Vigeant, Margot, Michael Prince, and Katharyn Nottis. "Repairing engineering students’ misconceptions about energy and thermodynamics." Teaching and learning of energy in K–12 education. Springer, Cham, 2014. 223-236. https://link.springer.com/chapter/10.1007/978-3-319-05017-1_13

Part 5: Using Science to Learn Chemistry

Burning Magnesium: an introduction to synthesis reactions

What would it be like to learn chemistry if the teacher didn't have all the science answers? What if we had to rely on science to figure out what was going on? Curious what this might be like? Then check out my new lesson: “Burning Magnesium”, our introduction to synthesis reactions! We use observations and simple experiments to guide our reasoning and figure out what is going on. The job of the teacher is to share the conventions of chemistry work and coach students through the thinking processes that are part of doing chemistry. And just like in real scientific work, when we get stuck or find something surprising, we discover the need to learn new skills and ideas. Core skills like naming compounds and writing formulae are introduced only when students encounter a situation that requires these skills! Feel free to explore the lesson and PowerPoint below or read on for a pedagogical tour. Enjoy!

PowerPoint and Experiment Videos (you need to download the ppt and open it in ppt to use all its features)

Student Investigation (pdf)

This is the seventh lesson of the chemistry unit, so students have had six lessons that introduce and prepare the skills you see in this investigation. For the larger context and lesson sequence, check out the full unit (well, at least for the lessons I have written so far!).

A Careers Context. This lesson describes a scenario that is an example of the professional use of chemistry skills. We are doing a bit of role-playing by imagining that we work for a safety organization that has received a complaint about a product. We must determine the chemical products from the use of sparklers are decide if they are hazardous.

A Safety Focus. Every time we encounter a new substance, students look up its safety characteristics in a compilation of SDS sheets that each group will have. These will be printed out and placed in the basket of materials for each group, ready to be used each time a new substance comes up. Safety is all about establishing good habits and routines. This seems like a pretty good one.

Particle Pictures. An important part of learning science is the development of conceptual models that help us represent and explain our understanding. We regularly use particle diagrams to show the arrangement of particles in substances before and after a reaction. This activates a lot of good scientific thinking that benefits from regular reinforcement. We start drawing these diagrams in grade 9, so the diagram shown below would be nothing new for our students.

Scientific Questions. We burn magnesium and observe evidence of a chemical change, but we don't have someone to tell us what the reaction product is! (The teacher is curiously silent on this.) The scientific questions that help us figure this out are an important window into both the world of chemistry and its history. There was a time in the past when no one knew what the result of burning magnesium was. It could be reacting with all sorts of things in the air! So we come up with possibilities: the magnesium could be reacting with substances like oxygen, nitrogen, carbon dioxide, argon, and many more. These possibilities turn into hypotheses which we then test and eliminate. This important thinking process gets to the heart of doing science; this is how we come up with convincing explanations for how our world works. The example of burning magnesium was chosen because its cool (well, actually hot) and its products can be easily captured and measured (which shows a very interesting increase of mass!). Here is how we generate one of our predictions:

Another possible product is magnesium nitride (our rival prediction). Afterall, there is much More nitrogen in the air than oxygen. Until we do the science, we just don't know what the product is!

Naming Compounds. Even though we are in our seventh lesson of the chemistry unit, this is the first time we encounter a compound whose identity we don't know but who's composition we do (or at least that we predict). It is only now, in the example above, that we have a genuine need to name a compound! Before this, we were simply told the names of compounds as we started using them - the names were on the jars. This is a good example of the practice of introducing new skills only when they are needed. The skill is now relevant and immediately useful because we need to talk about this compound!

Proportions of Elements Simulations. Historically, a lot of painstaking work went into the determination of the proportion of each element within a compound. In this lesson we introduce the well-known “criss-cross” technique to produce a formula such as MgCl2, which is an amazing labour-saving strategy. But there is always a danger when we introduce shortcuts: the science that lies beneath them might be obscured or never really fleshed out. The differing ionic charges of magnesium and chlorine lead to the 1:2 proportion of elements in this compound. This arises naturally from the electrostatic interactions of these particles and their random motions! They just bump around until they settle into these proportions (thermodynamics is awesome). To illustrate this, I created two simulations:

Representing Chemical Reactions. Each chemical reaction is interesting and special! To build understanding, we represent a reaction in multiple ways in a Reaction Chart. This pedagogical strategy, using multiple representations, has been shown to deepen student conceptual understanding. Each different representation highlights or illustrates different aspects of the chemical reaction. The representations reinforce one another by encouraging accuracy and consistency. They also help students to bind differing ideas into one robust understanding of the reaction. This doesn't happen when skills are mostly used in isolation, in long lists of practice questions. There is a lot of understanding and skill required to complete one chart: each element of this chart separately can become rote work but together they form a rich task.

Energy. Energy is an important and underused idea in high school chemistry that should be a part of most chemistry units and discussions, even at beginner levels! Introducing energy concepts and particle pictures helps bring chemistry concepts alive in the minds of students: they make chemistry real. They also bring a tremendous amount of predictive and explanatory power that is strongly motivating. We all want to know the answer to “how” and “why” questions: this is what drives scientists and students alike; we need to make sense of our world. (In a previous lesson, we add calcium to warm and cold water and predict what will happen. It’s a nice result!) Since this is the grade 10 level, we keep our use of energy simple:

Skills Practice. Rather than doing pages of exhaustive practice focusing on nomenclature, balancing equations, and other key skills, we introduce these in small pieces and use them regularly throughout the unit. The skills will become more complex as the lessons progress and will get regularly reinforced through repeated use in interesting contexts. Each application of a new skill quickly combines with other skills, so they are seldom used in isolation. The homework exercises are connected to a meaningful context, so students are never just moving around symbols. Here is a traditional set of exercises to practice naming conventions:

We will end up learning only a fraction of this. Why? Knowledge and skills need to be useful, otherwise they don’t form cognitive connections and stick in students’ minds. This is why skills such as these can evaporate almost completely by the time students reach grade 11 chemistry. Please consider: will students be using any “nona-“ compounds in grade 10 chemistry? Will they be learning about or working with any chemical process is that involves “hepta-“ substances? The exhaustive approach to teaching these skills is exactly that and no more: exhausting. It doesn't prepare students for later study when the introduction of content is so far removed from any plausible, meaningful application. So, our list of prefixes will be smaller (along with our list of multi-valent atoms and polyatomic ions)!

Our first exercise using the skill of naming covalent compounds is given with a meaningful context and is done as part of the exploration of a synthesis reaction:

Why this works and why it’s important

Learning is so much more interesting and enjoyable when:

(1) there is a meaningful context

(2) there is an emphasis on making sense of what is happening

(3) we can make and test surprising predictions

(4) we are not overwhelmed with content that is not used in a meaningful way

These four factors are critical elements that will help us adapt to our teaching practices so a wider range of students in our class are engaged and successful. At first glance, a lesson such as this might seem much more challenging and complex than a traditional lesson. But by trimming out un-useful content and carefully, incrementally building skills, average students and traditionally less successful students can do amazing things. And don't underestimate the motivational power of being able to make and test predictions - it has an amazing effect on students.

If you have any feedback for me about this discussion or lesson, I would be most happy to hear! As I have mentioned, I am not a chemist so I still have lots to learn and always appreciate your thoughts.