Tag Archives: modeling

Chemistry, more like cheMYSTERY to me! – Democritus

Quick recap from the first post of this series: I start the year with some underpinnings (scientific process skills that are necessary to survive in a Modeling classroom) activities. It is there that we establish how to build a scientific model.

Continuing my series on model building,  let’s talk about Democritus. 

Democritus’s Atomic Theory is the foundation for all of chemistry and is incredibly relevant today. This is where the chemistry Modeling Instruction curriculum starts. Democritus made the observation that if you break a rock into tiny pieces, those pieces are still made of rock. He then inferred  that if you broke that rock into tiny particles so small we can’t see them, they would still have the same rock composition. Therefore, all matter must be made of teeny tiny indestructible particles that Democritus called atoms (I don’t use the word atom until we get to Dalton to avoid confusion about compounds). The first model of the atom was born! There are some other parts to Democritus’s model like the properties of atoms are determined by the shape of the atom but I don’t address that.

I start all of chemistry with the above story about Democritus and tell my students that this is our current model of the atom because we do not have any other evidence to tell us otherwise. Then I do the exploding can demonstration because chemistry is all about blowing things up, right?

Exploding Can Demo

The exploding can demonstration helps establish the practice of drawing particle diagrams. Students are asked to draw a particle diagram before the can is lit, while the can it lit, and when the can explodes. They come up with all sorts of explanations with their particle diagrams. Sometimes they are dead on, sometimes not. The right answer is not as important as the discussion of particles.

From the exploding can demonstration you can generate some particle diagram rules.  The 4 I always have them come up with are:

  1. Particles are represented as circles, not dots
  2. Different particles should look different
  3. Include a key so we know which particles are which
  4. You don’t need more than 20 particles in your diagram

I always get at least one group that tries to represent particle motion with whooshies or arrows. When I see this I ask, “why are there lines coming off your particles?”, to which students usually reply, “because it’s a gas and gas particles are always moving.” I then ask, “do you have any evidence that particles move?”, to which students usually reply, “yeah, my 9th grade science teacher told me they do!” I followed that up with, “but how do you know?”  It sometimes takes a few more questions to convince the students that particle motion is not currently in our model but we may add it later if we have evidence to support it. I do not tell students how the exploding can works here because they do not have the background knowledge to fully appreciate the chemistry. Instead I bring it back on the last day of class and have the students try to explain it again with their more robust model of the atom.

The discussion of particles and particle diagrams leads us straight into the “Mass and Change Lab.”

Mass and Change Lab

The “Mass and Change Lab” is a fairly standard conservation of mass lab. I have edited the lab so it is not exactly the same as what is in the Modeling Instruction materials but it includes a variety of chemical and physical changes that gain, lose and keep the same mass (depending on how you define the system). I have students use triple-beam balances  during this lab to continue to reinforce the concept of significant figures.

After every group has collected their data, I have the class compile their data on the main board in the class. Each group writes whether the experiment gained or lost mass and if so, how much? The data will not be perfect. You can usually spot which groups forgot to account for the mass of a test tube or beaker and use it as an opportunity to talk about sources of error. Once we have established the mass change for each experiment, we whiteboard a before and after particle diagram for each mini experiment.

During this whiteboard session I ask students, “how are you going to show if the mass changed or stayed the same?” This is where students make the connection that the number of particles represents the mass.  If the system gained mass, it must have gained particles. If the system lost mass, it must have lost particles. Students can then answer the questions, “where did the extra particles come from?” or “where did the particles go?” These questions can lead to a discussion on “what is a system?” and “what are open and closed systems?” After we have established particle diagrams for each mini-experiment, I ask students to come up with a definition for the Law of Conservation of Mass. The class usually comes up with something like “the total number of particles stays the same in a closed system.”

Now that we have established that the number of particles represents the mass, we can move on to density.

Mass and Volume Lab

I introduce the concept of density with a set of density balls I got from Education Innovations.

The two balls have the same mass but the smaller one feels heavier than the larger one. I ask students to account for this observation by drawing particle diagrams of both balls. I do not give this explanation the name “density” yet. We simply discuss it in terms of “the mass to volume ratio.”

Next we do the density lab. I have a few sets of aluminum cylinders and PVC cylinders of various sizes that I use for this lab. Any standard density lab kit would work. I ask students to find the relationship between mass and volume for the aluminum pieces and the PVC pieces. At this point in the year the students are well versed in finding relationships so I set the students loose to collect and graph their data. They come back with completed whiteboards and a lot to discuss.


Students quickly see that their data split into two lines so they have to calculate two slopes and write two statements of relationship. On the boards pictured above, you will notice that I have my students additionally draw in the line for water so we can determine if the pieces will sink or float (steeper slope than water will sink, a shallower slope than water will float). I also have the students represent both substances with particle diagrams so they have a quantitative and qualitative representation of density. I ask many questions throughout the board meeting like, “what would be more massive, 20 mL of aluminum or 20 mL of PVC?” Or the converse, “what would take up more space, 50 g of aluminum or 50 g of PVC?” At the end of the whiteboard discussion, we establish that the slope is the mass to volume ratio which we call “density.”

I follow up this lab with some worksheets on density adapted from the Modeling Instruction materials with qualitative (particle diagram) and quantitative (graphing and proportional reasoning) density questions.

I also give students a density practicum based off of Flinn’s “Don’t Sink the Boat” activity.

Once students are comfortable with the densities of liquids and solids, we can determine the density of a gas.

Density of a Gas Lab

The “Density of a Gas Lab” is a standard collection of gas by water displacement (see Flinn’s “Scientific Laboratory Techniques Guide” for a good diagram). The gas is CO2 generated by Alka-Seltzer and water. Outlining the procedure for this lab can be a little cumbersome but my students always get great data (though there are always a few groups that need a few tries to get there).

After students have collected their mass and volume measurements of the gas they collected and calculated the density, I have them record their data on the whiteboard in the front of the room. Immediately students notice that the density of a gas is a really small number. I have students put that number in scientific notation and compare it to the densities (in scientific notation) of liquids and solids we know of. This allows us to discuss the term “order of magnitude”. I ask students “how many orders of magnitude greater is the density of water compared to the density of carbon dioxide?” Students can easily determine water is three orders of magnitude denser. What students don’t realize is that means water is 1000 times denser than carbon dioxide! That usually catches them off guard so I ask them to represent the average densities of solids, liquids and gases in 3 particle diagrams.

Students either overthink it and want their particles diagrams to be exactly quantitatively correct or they underthink it and just draw each diagram with an arbitrarily smaller number of particles. Each group presents the reasoning behind their boards and we compare each board to the actual data. After a few comparisons, students realize that to truly represent the density of a gas, they would have to draw a fraction of a particle. Since fractions of particles do not fit our model, they settle for drawing one particle in the gas particle diagram. This representation is not congruent with many textbook particle diagrams and is a big misconception among students.

We have now learned all sorts of things about how the number and arrangement of particles affects properties of matter but we still have one burning question; how tiny are these tiny particles?

Thickness of a Thin Layer Activity

I wrap up the first chemistry unit with the “Thickness of a Thin Layer” activity from the Modeling Instruction materials. In this activity, students must determine the thickness of a piece of regular foil and the thickness of a piece of heavy duty foil using what they know about the density of aluminum (calculated in density lab).

From this activity, students can determine a minimum particle size if the aluminum foil is 1 particle thick (the heavy duty foil is about 1.5 times thicker than the regular foil, so the minimum particle size is 1/3 the thickness of the heavy duty foil). I then show students a clip from “The Ring of Truth” about particle size. The examples in the clip get the minimum particle size down even smaller. You could also drop a known volume of oleic acid in a large bowl of water, calculate the area of the circle it forms and then calculate the thickness of the layer to get a smaller minimum particle size.

I wrap up the discussion by showing students the “Scale of the Universe” applet. This site does a great job of putting the size of a particle into perspective for the students (as well as the size of the universe). Make sure to show it with the sound turned up, the music is awesome!

That is the end of the first chemistry unit! To sum up the model so far…

  • All matter is made of tiny,  indestructible, hard sphere particles
  • The number and size of the particles determines the mass of the substance
  • The number of particles in a closed system does not change
  • The number of particles in a certain amount of space determines the density of the substance
  • Particles are really small; on the the order of 10^-9 m or 1 nanometer.

Chemistry, more like cheMYSTERY to me! – Underpinnings

One of my clever students wrote this on a whiteboard my first year of teaching. It was a  classic “ha ha, hmmm…” moment.

I love the creativity, but that’s not really how you want your students to feel about chemistry! I bet a lot of students could empathize with this whiteboard. So how do we take the mystery out of chemistry?

I think the biggest “mystery” of chemistry is “how do we know?” How did scientists figure out what particles that are too small to see look and behave like? Early chemists like Dalton, Thomson and Rutherford often get passed over in chapter 1 of a textbook. They provide some interesting trivia questions, but nothing more. It seems like the best way for students to understand tiny particles is to observe them the same way Dalton, Thomson and Rutherford did. Enter Modeling Instruction.

I will be posting a series of entries throughout the school year under this title summarizing how the model of chemistry evolves in my class throughout the year. My curriculum ia based on AMTA’s Modeling Instruction curriculum with some tweaks.

The first topic of this series is “underpinnings.” Underpinnings are all the skills necessary to study chemistry that are not necessarily related to chemistry content. This includes the nature of science, calculating slope, stating scientific relationships, sig figs, and unit conversions. You can check out my 180 blog for specific activities I do to address these topics. For now, I want to discuss just the nature of science.

The nature of science is often taught at the beginning of the school year and then ignored for the rest of the year. The beauty of Modeling Instruction is that the nature of science is a thread that is woven throughout the curriculum. For students to really appreciate that thread and understand the model of chemistry, you need to establish the nature of science well at the beginning of the year. Specifically, you need to address the idea of building a scientific model.

The model of chemistry started with an observation. That observation combined with an inference became the first model of a tiny particle. Eventually an observation was made that did not fit that model, so the model had to be amended with the new observation and a new inference. Eventually an observation was made that did not fit the new model and the model had to be amended again. And on and on it goes as better technology leads to better observations. This is the story of science. This is the idea I come back to over and over again throughout the year. Even our current model of chemistry is only the model so far.

I teach this idea of “model building” using the wax block activity (see 180 blog). I love this activity because it is both a discrepant event and a black box. Students make an observation and combine that with an inference to describe how the block words. When they are given flashlights (new technology), their observations may not fit their previous models. That is okay, models can change. When the students are given laser pointers (even newer technology), their models might change again. When the students collaborate with other students, their models might even change again! Of course (to the students’ dismay), there is no answer key for science. All you have is your evidence-based model (so far).

EDIT: I have gotten a lot of questions about the wax block activity over the last year! I wanted to offer some answers to everyone in case you have the same questions. I make these myself buy you can find instructions from Flinn here. You can buy parafin blocks at your grocery store with the pickling supplies. I also put together a script I use that loosely outlines how I structure the activity here. Here are some pro tips as well:

  1. Make sure the foil is smaller than the blocks. Inspect the sides of the blocks carefully to make sure you cannot see any foil. Students will get curious if they see something and scratch away the wax on the side of the block.
  2. If you need to break the block apart to redo it, just smack the side of it on the countertop a few times, it should come right apart. With that said, at least one of your blocks will get dropped and it will break open during class. Be on high alert so you can swoop in before the magic is ruined!
  3. Don’t let your students get away with an easy answer. They will likely draw you a picture of “something” inside the block but not elaborate. This is a good opportunity for students to make more observations and then infer what that “something” could be. Given them a flashlight, put the block on top of objects of different colors, etc.
  4. Don’t tell them the answer. This is the hardest part! Students get so excited about this activity and at the end all they want to know is “was I right?” This is a perfect opportunity to start building your classroom culture. It’s not just about being right! These wax blocks will come back to haunt you for the remainder of the school year but stay strong!

This is one of my favorite activities of the year. Students ask me about it until the last day of school. Let me know how it goes for you and feel free to message me with any questions!

This theme will come back again and again. My goal for this year is to get my students to truly understand what a model is and how having a model helps us to build a problem-solving framework. I foresee the question, “what’s your model” being asked frequently this year.

Next up in the series: Democritus and his tiny particles

Building a Model: Part 3 – Weekly Reports

Week 2 of the advanced workshop was quite busy! In addition to talking about alternate problem types, we also talked about a useful tool called weekly reports. Weekly reports were developed by Eugenia Etkina and are outlined in her paper “Weekly Reports: A Two-Way Feedback Tool” (2000). The purpose of weekly reports is to make students’ thinking visible and consists of 4 questions (I edited the original wording a bit):

  1. What do you think you learned this week?
  2. How did learn the things you named above?
  3. What questions do you still have or what is still unclear to you?
  4. What questions do you expect the teacher to ask you tomorrow about what you have learned?

The point of these questions is to get students to actually verbalize what they think they have learned which is often different than what the teacher thinks the students have learned. The use of standards-based grading and clear learning targets should help students understand what they are expected to learn each week.

The questions in the weekly report get progressively more difficult for students to answer. The “what” question is pretty straight forward but “how did you learn it” is more difficult to answer. This question forces students to think about how the model was built. The next question, “what is still unclear?” makes students think about their weaknesses which is often more difficult than thinking about strengths. Students may be tempted to answer “question 2 on the homework was difficult” instead of identifying a particular concept. The last question is probably the most difficult to answer because the student must think like the teacher. The purpose of this question is to see if the student can identify the most important concepts learned that week.

A lot of diagnostic information can be drawn from weekly reports but my first thought as a teacher (and the thought of many others in the workshop) was “that sounds like a lot of work!” The question then becomes, how can you streamline this process?

I started by making a Google Form with these questions and embedding it in my website. This way all of my student’s responses will be dumped into one spreadsheet which is easier to sort through than a pile of papers. I may also distribute the first weekly report through Doctopus so I can give feedback easily. Another way to cut down the work on these weekly reports is to not make them weekly. A bi-weekly report might be more fitting in a high school setting.

I’m going to jump on the weekly report train next school year and try to work out the bugs along the way. Progress posts to come!

P.S. Wouldn’t it be great if I could change the name to TPS reports? Summer project: work on that acronym!

Building a Model: Part 2 – Alternative Question Types

Week 2 of my advanced modeling workshop has come and gone and we spent a lot of time with alternative question types. As teachers we are always looking for ways to keep our classes fresh. One way to do that is through alternative questions types like ranking tasks, jeopardy problems, context-rich problems and goal-less problems.

I knew about all of these question types before coming to this workshop but I realized this past week that I have no idea what I’m doing!

Through a lot of readings (see problem-type summaries below), I now have a better understanding of alternative problem types and how to use them. The biggest mistake I was making with all of these question types was letting the first time students see these new question types be on an assessment. This is a big “no no” because students need time to practice and adjust to these somewhat unfamiliar and perhaps uncomfortable types of alternative problems. Make sure to set your students up for success with these new problem types!

Here is a little bit about each type of problem:

Ranking Tasks

Ranking tasks might be my favorite type of alternative problem. Check out the articles “Ranking Tasks: A New Type of Test Item” by David Maloney (1987) and “Ranking Tasks Revisited” by Maloney and Friedel (1995) for an academic overview of this question type.

A ranking task question gives student 4-8 arrangements with the same basic structure but different numbers or data. Student need to rank the items based on given criteria and explain their reasoning for their ranking. The great thing about ranking tasks is students must figure out what variable they are looking for on their own. This question type also gives teachers the chance to see how students think, not just their answer.

For our nuclear chemistry unit, I wrote a ranking task using mass spec data and average atomic mass. Students have to rank the elements represented by the data from least massive to most massive. To solve this problem, students need to understand the graphs they are looking at and then know how to pull data from the graphs to calculate the average atomic mass of each sample using a weighted average.

Screen Shot 2015-06-22 at 9.11.27 AM

Jeopardy Problems

Jeopardy problems are another fun type of alternative problem. A jeopardy problem is just like the iconic game show, you give students the answer and they give you the question. Again, for an academic overview of this problem type, see “Playing Physics Jeopardy” by Alan Van Heuvelen and David Maloney (1999).

There are two types of jeopardy problems: equation and diagram/graph. An equation jeopardy problem gives students the complete equation for a problem and the students must come up with a scenario that fits the equation. I might give students the following equation:

Q = (205g) (4.18 J/g°C) (56°C – 14°C)

Students would have to come up with a scenario that this equation could describe. An acceptable answer is a pot of cold water, starting temperature 14°C, is heated on a stove to 56°C. Students must truly understand each variable in the equation to answer this question. The question could be made more difficult by using multiple equations.

In a graph/diagram jeopardy problem, students are given a graph or diagram and must provide a scenario that the graph or diagram could represent. I might give students an LOL chart like the one below and have them come up with a possible scenario for it. A possible solution for this problem is a pot of hot liquid water is vaporized into a gas.

Screen Shot 2015-06-22 at 9.25.02 AM

Jeopardy problems are a great alternative problem type because they evaluate how well students understand the equations and graphs you use in class.

Context-Rich Problems

Context-rich problems are great for chemistry because there are so many real-world applications students can explore. I love context-rich problems because they answer the question “why do I have to learn this?” Check out this overview from the University of Minnesota for a really practical approach to context-rich problems.

The key to context-rich problems is they start with “you.” The problem must give students motivation to solve it. For the nuclear unit, I wrote a context-rich problem about radioactive reindeer in Norway.

Screen Shot 2015-06-22 at 9.44.40 AM

This problem gives students motivation to solve the problem, students are not explicitly told what they are solving for and it is multi-step problem. I try to give students a context-rich problem within every unit as a group challenge problem.

Goal-less Problems

Goal-less problems are probably the most uncomfortable type of alternative problem for students because they are so open-ended. A goal-less problem provides students with a scenario but no question. Kelly O’Shea has a great blog post about goal-less problems in physics class. I love combining goal-less problems with standards-based grading because the learning targets give students a road map for providing solutions to the problem. A great use for goal-less problems is as reassessments. You can give students a scenario and have them apply the information to the learning targets they want to reassess.

A sample goal-less problem I have used in chemistry for my heat and temperature unit is giving students a mass and having them roll a die to get a starting temperature. See the problem below:

Screen Shot 2015-06-22 at 10.09.32 AM

Goal-less problems really show what aspects of a model students understand and what aspects they struggle with. The goal-less problem is also easy to differentiate because you can ask students to take it further if you give them feedback as they work.

Hopefully this gives you some ideas for keeping your assessments fresh and engaging! Happy planning!

Building a Model: Part 1

Happy summer to all you teachers out there!

While I am very excited to have regained my bathroom freedom, I am even more excited about the PD I have planned for this summer. This summer is all about the modeling!

I am currently at  an advanced modeling workshop for the next 3 weeks and I thought this would be a good place to synthesize what I have been learning. The purpose of the advanced workshop is to construct a modeling unit from the ground up. The first week (and the topic of this post) consists mostly of defining your model, building your ladder of knowledge and filling in possible activities.

Step 1: Choose a Topic

This sounds deceptively easy. My group started with the topic “modern atomic theory.” Seems doable right? We soon found out that this topic was leading us straight into other topics like nuclear reactions, electronic structure and periodic trends. We concluded we either needed to take the nuclear route or the electronic route. Nuclear route won because we felt like we had less materials to address this topic.

Step 2: Define the Model

Once we had a topic, we needed to define our model. The model is the framework that all the content in the unit will be built on. A unit can contain more than 1 model. Our nuclear chemistry unit has 2 model statements:

  • The atom is divisible into smaller subatomic particles, which determine the identity of the atom and have different electrostatic charges and masses.
  • Atoms of one element can change into atoms of another element through radioactive decay.

These model statements are the guide for our entire unit. Our students must be able to complete the objectives of the unit using the above models.

Step 3: Build the Ladder

The next step was to build a ladder of content we want the students to know throughout the unit. The hardest part about this step was thinking only about content, not activities. As teachers, we are always thinking, “what activity do I have for this topic?” With a topic as broad as nuclear chemistry, it would be really easy to put together a bunch of fun activities that only dance around the content we were aiming for. The ladder helped us pinpoint exactly what we wanted our students to get from the unit and then we could fill in the “how.”

For nuclear chemistry, we wanted to build off the AMTA Modeling materials. Our students already knew about the Democritus, Dalton and Thomson models. Our nuclear unit needed to start with Rutherford. We decided to continue in the tradition of the Modeling curriculum and structure our unit historically. Our ladder looked something like this:

  1. Rutherford (nucleus is a dense positive charge in the center of the atom)
  2. Mosely (atomic number is what defines an element, not atomic mass)
  3. Chadwick (the nucleus is composed of positively charged protons AND neutral neutrons)
  4. Fermi (unstable nuclei can decay at a predictable rate, releasing a large amount of energy that can be harnessed to produce electricity)

Step 4: Fill in the Activities

Our last task of the week was to start filling in the activities. Again, another task that sounds deceptively easy. This task was especially difficult because we chose a very abstract model. Students cannot physically see the nucleus of an atom, so how do we convince them it is there? Between analogous activities and pHet simulations, we were able to make the abstract idea of the nucleus more concrete.

The trouble we ran into along the way was we were so concerned about making everything concrete, that we were losing some of the content in our analogies. At some point, every analogy fails. In the end we had to remember that our audience is intro level chemistry students who do not need every single idea spoon fed to them. We kept the strong analogous activities, like our Plinko style board to show the Rutherford model of the atom, and threw out our weaker analogies, like our weighted blocks to show the extra mass the neutron adds to the nucleus.

By the end of the week we had a pretty solid unit and were able to assign tasks to every group member. Building a model from the ground up is incredibly work intensive but it really forces you to understand the framework of Modeling Instruction.

If you haven’t been to a Modeling workshop, add it to your to-do list. Check out modelinginstruction.org for dates and locations. Happy curriculum writing!

Take chances, make mistakes, get messy!

One of my science teacher heroines is Ms. Frizzle from the magic school bus. Remember her teaching philosophy?

I need a poster of this in my room so I can point to it when my students ask their favorite question; “is this right?” This question hurts my soul for a few reasons…

1. Students just want a yes or no answer

2. There is no emphasis on the process, just the answer

3. The question is usually accompanied by the statement “I don’t want to be wrong”

Somewhere along the way we taught students that it is not okay to be wrong. At some point we told students that the process doesn’t matter, you only get credit for the final answer. Most importantly, we taught students that it is not okay to make mistakes. Ms. Frizzle would be seriously disappointed.

So how do I combat this in my classroom? I use two tools:

1) Modeling Instruction

2) Standards-Based Grading

Modeling instruction helps me battle the dreaded “is this right?” question by simply never answering it. I reply to every question with another question. I always start with “I don’t know, what do you think?” so the student is forced to explain his or her reasoning. If there are blatant errors, I may pinpoint a particular spot and ask “why did you do this?” If there are no errors I might ask “are you confident in your reasoning?” I never give a “yes” or “no” answer.

Standards-based grading allows students to make mistakes on assessments and be given a second chance… and a third chance…. and a fourth chance…. and even a twentieth chance if it comes to it! Students are assessed multiple times on a single learning target and always have the opportunity to initiate their own reassessments. Students are not penalized for learning at different paces as long as they learn. That is the objective after all.

These two strategies together have helped shift the culture in my classroom from one of rote memorization to genuine learning. Do students still ask “is this right?” Of course they do. Now I just sit back and smile as another student in the room answers before I can, “I don’t know, what do you think?”

What’s in the bubbles of boiling water?

I asked my students this year “what is inside the bubbles of boiling water?” Without hesitation, all 24 students in my advanced chemistry class answered “hydrogen and oxygen gas.” These students were sure of their answer because they knew that water is made of hydrogen and oxygen.

A typical chemistry class is taught from the top down; you start with the most complicated model of the atom and go from there. Do you really need the electron-cloud model of the atom to understand the gas laws? What about thermodynamics? What about bonding? Yes, I teach bonding without the electron-cloud OR Bohr model! The boiling water misconception is why.

My chemistry class starts with the Democritus model: everything is made of particles. This does not mean everything is made of atoms. Students may describe air particles, water particles, desk particles and even students particles. We use this model to explore mass, volume, and density. Then we observe diffusion and infer that particles must be moving and particle speed corresponds to particle temperature. This inference allows us to explain the gas laws and thermodynamics.

Let’s stop here for a second. If my students had no prior knowledge and I asked them “what’s inside the bubbles of boiling water?” at this point in our curriculum, they certainly would not answer “hydrogen and oxygen gas.” They would think more simply and answer “water gas particles.” Misconception averted.

Continuing on, after finishing our thermodynamics unit, the students observe water being broken into two separate gases in the Hoffman apparatus and must infer there is something smaller than a water particle. Those smaller particles can somehow “hook” together to form new substances. This is the Dalton model. We use the Dalton model to explore mixtures and pure substances as well as the Laws of Definite and Multiple Proportions.

Next, the students observe electrostatic attraction and must infer that particles have a mobile negative charge. This is the Thompson plum pudding model. This model gets my students through bonding. We talk about bonding in terms of attractions and physical properties instead of anthropomorphizing the octet rule. The Thompson model takes us through moles, chemical reactions and stoichiometry.

It is not until the end of the year that we observe graphs of ionization energies to infer that electrons exist in different energy “levels” which leads us to the Bohr model. My students then leave my classroom with a deep conceptual understanding of chemistry and how the world works at the particle level as opposed to a disjointed collection of equations and rules.

Chemistry was not discovered by reading textbooks so why should we teach it that way?

I cannot take credit for any of this. This concept was developed by the wonderful people at Arizona State University and is part of the Modeling Instruction curriculum. Find a workshop near you this summer at modelinginstruction.org.