The Carrot Incident: Address to the OCU 2016 graduate commencement

GradSpeechSmThe following is the prepared version of the address I gave at the Oklahoma City University Graduate Commencement on May 7, 2016.

If you would rather watch the speech, it begins at 24:00 here.

When I was asked to give the graduate commencement address, I started thinking about my own graduate commencement. I spent five years in the alternate universe that is grad school, but that was coming to an end and I had to decide what to do next. My choices were to either stay in science and move to a new lab somewhere else, or I could do something different.

In the back of my head I’d always had this crazy idea about teaching high school science. For advice I turned to a very influential person in my life, my high school chemistry teacher, Cynthia Macarevich. When I took chemistry from “Mrs. Mac” just down the street here at Northwest Classen, it was an epiphany.  The angels sang, the light shone down and I knew that chemistry was the thing I both loved and was good at.  And I wanted to be the kind of teacher that made his students feel the same way.

Macarevich was very encouraging and told me she’d contact some friends. About a week later I had first an interview, then a job offer to teach science at a brand new school, Harding Charter Prep High School, here in Oklahoma City. The moral of this part of the story is, be nice to your teachers, they may get you a job someday.

By the day of my own graduate commencement, the day I got this hood, I knew I was going to be a high school teacher. I was excited and maybe a little over-confident, because I was going to be the best science teacher ever. The reality, of course, was somewhat different.

I struggled through my first year of teaching, which is always the toughest, then one day my second year of teaching in my intro chemistry class and I was giving a lecture about color. As an example I was using beta-carotene, the compound that gives carrots their orange color. I had this whole back story about not all carrots being orange. Some are in fact white or yellow, even purple, and the orange color we have today was carefully selected by growers in part to please the royal House of Orange, which my students were also studying in European History. In the middle of what I thought was this great lecture a student raised his hand and said “OK, I’m confused, where do carrots come from?” This caught me off guard, but I started to say “You know, you put the seed in the soil and you water it,” when the student interrupted me, “Wait, you mean carrots are plants?”

I paused a moment and said “Of course they’re plants.” After another pause I said “Who was your biology teacher last year?” I already knew the answer, of course, but the student had to think about, then he said “You were!”

This was a turning point in my teaching career. It bothered me for months. This moment, which I now think of as “The Carrot Incident”, crystallized a year and a half of frustration, of realizing I was not seeing the results in my students I wanted. In spite of the hours I spent working on my lectures and preparing clever lab experiments for them, they weren’t learning. This was obvious to me every time I graded an exam. When my students did “learn” I had trouble pushing them past the level of memorization. They weren’t learning science in my class. Most of the time they were copying down notes and failing to make any sense of them.

The Carrot Incident forced me to begin to rethink the way I was teaching. You see, I couldn’t blame anyone else for this. I was this students’ teacher, and I had every opportunity when I taught biology to have my students grow plants from seeds, to water and care for them, to measure and observe their growth, to study their flowers, to pollinate them. It would have been a simple, inexpensive and really effective project, but one that never occurred to me. I could have had them handling real fossils and not just talking about them, I could have had them doing reactions and making measurements instead of focusing so much on symbols and equations. In other words, I could have had them doing science instead of telling them about it.

I was also beginning to realize I had been making a lot of assumptions. I was assuming these kids would be able to learn the same way I did. I was also forgetting that I grew up in a house with garden in the back and helped out with planting, harvesting and at least sometimes eating what came out of the garden. I was beginning to realize that I had layers of assumptions and biases about what teaching looked like and that I would have overcome these to become a better teacher.

As a new teacher you wonder “Maybe it’s just my students”, but one year I had the opportunity to be a grader for the AP Chemistry exam. That year they locked 250 of us in a barn at the Nebraska State Fairgrounds for 7 hours a day in absolute silence. Over 8 days we graded 100,000 exams.

I was assigned what I thought was a simple essay question, but most students (mind you, theses are the best and brightest high school students in the nation) received either 0 or 1 out of 8 possible points. These were not blank pages, these were page after page explanations that were completely wrong. Not just a little wrong. The exact opposite of correct. We had a lot of what we called “hard earned zeros”.

Other people grading that question were outraged at what they were reading. They kept saying, “Well, what I tell my students is….”.  And I wanted to scream “Apparently, it doesn’t matter what you tell your students.” Because out of the 1500 or so answers I scored that week, 2 papers were completely correct.

But that’s just it. What you say in a classroom setting doesn’t matter. The research is quite clear on this. What matters is creating an environment and situations in which students can talk and discuss their own ideas and confront their own misconceptions. It turns out that a bunch of people had already reached the same conclusion and figured out what to do about it.  And I was lucky enough to wander into a workshop they were giving at an American Chemical Society conference in 2005.

I learned from that workshop and many others how to teach in a completely different way. I almost never give a lecture anymore. My students walk into the classroom, sit in groups of 3 or 4 and work through activities that I’ve written. Those activities ask them questions that force them to look at data, then analyze, question, and argue with each other about the data. Somewhere in the middle the activity will introduce a new concept or an equation, then the students will apply that new knowledge, and walk out the door with the same chemistry they would learn if I were lecturing. I walk around and answer questions, usually with more questions. But most of the time I hide in the corner and listen as they figure it out on their own.

Along the way they learn not only the chemistry but also how to work with other people, how to manage their time and, most important, how to begin to be independent thinkers.

Getting used to teaching this way has taken a lot of reorganizing what I think it means to be a teacher. You have to understand that we are all part of, and are products of, universities. And universities are steeped in tradition. The university grew out of monasteries in medieval Europe, and you’ll notice that we’re still wearing their clothes. But we’re not just wearing their clothes, we’re still using their teaching methods.

The use of lecture in universities pre-dates the printing press in Europe, but it is still held in highest esteem in academia. We honor people by asking them to give a talk. Since I got this award my students have been teasing me that it’s funny that I, of all people, have to get up today and give a lecture.

Chemical education researchers have shown that after 5 minutes of a lecture about 90% of the students in the room have become distracted. So, graduates, I want to make two points, and then I’m done.  First, if you have kids, please plant a garden with them, or at least a window box or even a little container in the window. Their science teachers will thank you later. Every spring, Jennifer and I involve the kids in planting our garden. My son’s favorite thing to grow just happens to be purple carrots.

My second point and final point is that even though most of you will not become teachers or professors, you will be leaders in your company or your hospital or wherever you find yourself. And at some point, you will realize that something you have assumed, something you took for granted about your field, is completely wrong. You will have a Carrot Incident. And when you do, you will be frustrated and confused, but then you will start to see everything in a new light and suddenly you will realize that all of the evidence has been there, staring you in the face. You will also look around and find there are others who have the same problem, and then you can get to work figuring out how to do things in a new and better way.

Graduates, I wish you the best of luck, and Godspeed. Thank you.

Why particles matter

NaCl models

NaCl is an ionic compound consisting of a lattice of positive and negatively charged ions. Many students hold the misconception that it and all compounds are molecular compound.

The idea of atoms is the single key idea that separates chemistry from the alchemy. Atoms provide a non-magical explanation for the central tenants of chemistry from stoichiometry (the masses of compounds in a reaction are proportional to one another because of the ratio of atoms) to intermolecular forces (the properties of atoms within molecules explain boiling and melting point of compounds) to kinetics (the rate and energy of collisions between atoms controls the speed of reactions).

Given the importance of atoms it is odd that we do not focus on them more. We tend to focus more on number crunching and symbolic representations (think reaction equations) than on atoms. That, however, is changing as the research on misconceptions and multiple representations has forced us think harder about what it means to educate young chemists. Students need to learn to represent atoms, ions and molecules to gain a deeper and more expert-like understanding of chemical phenomena.

In 2014 I wrote an article for the Journal of Chemical Education’s special issue on the new AP Chemistry curriculum. That curriculum has a strong emphasis on particles – and in particular particle diagrams – not seen in more traditional curricula. I felt like that aspect of the curriculum was going to be tough for teachers to know how to approach and so wrote the article to fill that need.

My article about particle representations in the Journal of Chemical Education is now available as an open access article. It is free to read it online and distribute in any way. The only thing I ask is that you attribute the work to me when you share it. Otherwise I hope you will find it interesting and helpful to your practice of teaching chemistry.

How I stopped lecturing

How I stopped lecturing

When I finished graduate school I made an usual choice.  Instead of pursuing a post-doc I moved back to my home town, Oklahoma City, and became a founding teacher at a charter high school. And there I taught science the way I had been taught science, from high school through grad school. I lectured nearly every day. I also conducted labs that were similar to labs I had encounter in my own education, mostly labs that practiced skills and calculations we had already learned in lecture.

After two years of teaching this way I came across two problems. The first was my students weren’t learning anything from my lectures. Obviously this was my students’ fault (or perhaps their middle school teachers’ fault), since my lectures were nothing short of brilliant. The second and more bothersome problem was that the way I was teaching science had very little to do with how I had practiced science as a graduate student. In grad school I took on a project that had only vague rules to it. There was a chemical system (iron oxide nanocrystals) and a technique (I won’t bore you with the details), but that was it. The project was guided by speculation about previous data, then planning experiments, then collecting data, then speculating about the data, then planning more experiments, then more data. This problem bothered me more because there was no way to blame my students for this.

Somewhere in my brain, an idea was half forming, that maybe we could teach science starting with data. About the same time I had a disconcerting interaction with a student which convinced me that my students were learning very little and harboring significant scientific misconceptions (such as that carrots are not plants). Then I attended an American Chemical Society meeting in San Diego and attended a Chemical Education session that seemed to be mostly about AP and General Chemistry. The session was all about a teaching method I had never heard of called POGIL. I didn’t fully understand it, but later at the expo I met Jim Spencer, who helped develop the POGIL method and who pushed a book into my hand (under the unhappy eye of the textbook salesman) and said “Here, take this, you need to do this.”

POGIL would turn out to revolutionize my teaching. In that workbook were activities for students to be used in small groups in which the students were provided data and had to draw conclusions from it. In other words, they had to learn from the data rather than from me. The students finally had to do what I did in graduate school – construct their own understanding, starting from data. I immediately tried it with my students, and remember very clearly one of my most difficult, disengaged students telling me, “Dr. P, this is good.”

I had some fits and starts implementing POGIL the next year, but eventually I had a system down. I found that I was more successful writing my own activities for my students because at the time there were only college-level texts and I was working with sophomores and juniors at an urban high school. By my fourth year of teaching high school I was using POGIL nearly every day, either in lecture or lab. I now teach at the college level and I almost never lecture except on days when I have to convey algorithmic problem solving techniques like unit conversion. Otherwise my students work in small groups on the POGIL activities I have written and, without giving a lecture, my students learn the material and more. They also learn how to work in a group, to pace themselves, to take ownership of their learning and assess whether or not they understand. They learn not only the chemistry, but also a set of skills for being independent scholars.

While I was teaching with POGIL at the high school the POGIL Project, a group that teaches about and promotes the use of POGIL, began fostering projects for high school teachers that eventually produced workbooks for high school chemistry, high school biology, AP Biology and most recently a lab manual for AP Chemistry. Hundreds of teachers around the country are now using POGIL every day to enhance the education of their students. I was lucky to be a part of the early work on this, and I owe it to Jim Spencer for giving me a book and the POGIL Project helping me see a way to teach in some way other than through lecture.

If you want more information on POGIL, you can watch this video and visit the POGIL project’s website.

Learning and the ladybug picnic

My son and I were watching Sesame Street, and an (updated) version of the The Ladybug Picnic. The ladybugs appear one at a time, with three on each of four sides of a picnic blanket. My son (who is 5, and about to enter Kindergarten) says “Did you ever notice that four threes is twelve?” After he did this he counted it out on his fingers to confirm it and proved to me (and himself) that he was right.

My son has no formal education in multiplication. He doesn’t know anything about times tables, and would not know what an “x” between two numbers (or a dot, or any other symbol) means. He was given a set of data (in this case an image of four sets of three ladybugs), made an observation and double checked his conclusion.

I was delighted by his observation because (1) I am a proud papa and (2) it exemplifies my own teaching. I teach by having students work in small groups of three or four on inquiry activities that I design. Each activity starts with data − a graph, a table, an animation, or a set of molecular models to play with. Each day in class, my students talk, argue, and discuss the meaning of that data, and develop a better understanding of the material than they would if I just told them about it. It was affirming and exciting, then,  to see my son make the same sort of connection I help my students make in chemistry. If you give students the right data and a little prodding it is truly surprising what they can learn .

My answer to the question “What is Color?”

The Alan Alda Center for Communicating Science holds a contest each year to explain a complex scientific idea in under 300 words.  Those 300 words have to convey meaning (and here’s the hard part) to a 5th grader.  This year’s question was “What is Color?”  The finalists have been named and can be read and (in the case of the video entries) seen here.

My (non-finalist) entry is below.  I am posting it because I spent a fair bit of time writing it, so I both want it to see the light of day and receive feedback in the comments section or on twitter (@SGPrilliman).  So I hope you enjoy it and let me know what you think!  Make sure you check out the finalists at the link above.


What is color? That’s a really important question. When scientists say “That’s a really important question” it means “this isn’t going to be easy” so hang on!

Sometimes light behaves like a wave on the ocean. In this case color is the distance between the peaks of the waves. For red light, the distance from one peak to the next is 600 nanometers (one nanometer is one billionth of a meter). For blue light, the distance from one peak to the next is 400 nanometers. Light behaving as a wave explains why “Blu-ray” disks hold more video than DVD’s. The smaller the wavelength of the laser inside, the closer the grooves can be on the disk, the more data it holds.

That seems okay, right? But in the early part of the 20th Century it became clear that sometimes light was better described as a particle, not a wave. When light behaves like a particle, color is a measure of the energy of the particle. Red light particles have less energy than blue light particles. This is why cooler stars look red, hot stars look blue, and in-between temperature stars (like our sun) look yellow.

So which is it? Is color a measure of the distance between peaks in the waves, or is it a measure of the energy of light particles? The problem is, light is both a particle and a wave, so color is both the distance between waves and a measure of the energy of the particle.

Do you understand? Neither do I. Having two answers to one question is messy, but those are the best kind. Simple answers are boring. Messy answers lead scientists like me and future scientists like you to keep asking questions and developing a deeper understanding of our complex universe.



Which of these things is not like the other? Enthalpy of formation, enthalpy of atom combination and bond energy

I have had many questions about the difference between enthalpy of formation (ΔHf) values and enthalpy of atom combination (ΔHac) values.  I’ve also been told there is not much about ΔHac­ values on the internet (which is fine because it would probably be wrong).  Two deal with both issues simultaneously I’m writing this blog post. There are many ways to calculate the change in enthalpy (ΔH) of a chemical reaction.  This is because enthalpy (H) is a state function – the path taken from start to finish does not matter, only the starting materials (reactants) and ending materials (products). The most common ways of calculating ΔH are:

  • Experimentally (from doing the reaction and measuring the heat)
  • Estimating with bond energies (broken bond absorb energy, formed bonds release energy)
  • Using an equation based on the enthalpy of formation (ΔHf): ΔH=ΣΔHf(products) − ΣΔHf(reactants)

ΔHf values are based on the reaction of taking a compound’s elements as they exist at room temperature and atmospheric pressure and measuring the heat released or absorbed when the compound is formed.  In other words, the ΔHf for liquid water is the ΔH of the reaction

H2 (g) + ½ O2(g) →  H2O(l)             ΔH=ΔHf = − 286 kJ/mole

Notice that we have H2 and O2 in the reactants here because oxygen exists as O2 gas  and hydrogen exists at H2 gas molecules at room temperature and atmospheric pressure.  To make liquid water from its element, those elements have to be broken up into atoms then recombined into the compound. Most people use ΔHf values because it gets you the right answer and because… that’s what everyone else does.  Enthalpy of formation values have become one of those things you do not because you really understand it or because it’s the best way but because that’s how it’s always been done.

It turns out there is a better way to do this which is with enthalpy of atom combination values, ΔHac.  The ΔHac values are a measure of the change in enthalpy going from gas phase atoms to a compound.  For liquid water, the corresponding reaction is:

2H (g) + O(g) →  H2O(l)                 ΔH=ΔHac = − 970 kJ/mole

Why?  What difference does it make?  In terms of plugging into the equation, none.  It’s still products minus reactant values.  The units are kJ/mole, so you still have to multiply by the stoichiometric coefficient.  Why bother then? It’s worth bothering because the ΔHac values actually reveal the total bond energy present in 1 mole of a substance.  For gas phase water, the ΔHac value is – 926 kJ/mole, which is two times the O to H bond energy value of 463 kJ/mole.  The extra 44 kJ/mole for liquid water is the hydrogen bonding energy. The enthalpy of formation values do not give you the bond energy.  Enthalpy of formation values only tell you the relative enthalpy change going from the substances elements, which are almost always either molecules or solids.  As such, the enthalpy of breaking down the bonds in those elements is folded into ΔHf, making the value itself useless.  ΔHac values can be plugged in the equation and have intrinsic value. Bond energy is the real concept worth emphasizing here.  Most people don’t understand bond energy and, as a practicing chemist, bond energy is the far more useful concept for understanding new situations, if for no other reason than it doesn’t require tracking down obscure ΔHf or ΔHac­ values.  I’m pretty sure I used ΔHf values once in my entire physical chemistry graduate career.

One more example: carbon dioxide. ΔHac for CO2 = −1609 kJ/mole ΔHf for diamond: −394 kJ/mole What does the ΔHf tell you about bonding in CO2?  Basically nothing because mixed into that number is the breaking of bonds from graphite and O2.  Meanwhile, the ΔHac value tells you that the bond energy of the C to O double bond in CO2 is 805 kJ/mole.

Comments?  Typos?  Still confused?  Tell me in the comment section.

Here is the reference for the paper that first proposed using ΔHac values: Gillespie, R. J., Spencer, J. N., Moog, R. S.  “An Approach to Reaction Thermodynamics through Enthalpies, Entropies, and Free Energies of Atomization.”  J. Chem. Educ., 1996, 73 (7), p 631.

AP Chemistry Big Idea 2

I’mImage starting a series of blog entries on the Big Ideas of the College Board’s new AP Chemistry Curriculum [link] with Big Idea 2 because it’s a little easier to tackle off the bat than Big Idea 1.  Big Idea 2 states:

“Chemical and physical properties of materials can be explained by the structure and the arrangement of atoms, ions, or molecules and the forces between them.” – APCCF

A theme throughout this Big Idea is that students can move back and forth between particulate level representations, symbolic representations and macroscopic observations (which is Science Practice 1).  In other words, Johnstone’s triangle − the idea that expert students can move back and forth between the various representations − becomes very important.

For example, if the student is given LiBr as the formula of a substance they are expected to determine that it will be an ionic compound (LO 2.17), which means it will be a brittle solid (LO 2.19) that dissociates when it dissolves in water because of attraction between the ions and polar water molecules (LO 2.14), forming a solution that conducts electricity (LO 2.19 again).  Given NH3 as a formula a student is expected to determine it will be a molecular compound that dissolves in water because it is polar and forms hydrogen bonds with water (LO 2.15) but does not conduct electricity because it does not form ions but remains discreet molecules containing one N and three H atoms.  The student could also be asked to work with or draw pictures of all of this (LO 2.8) or design an experiment to determine the type of bonding present in an unknown solid (LO 2.22).  In other words, they would have to know you could try to dissolve the compound in water and, if it dissolved, test the conductivity to determine whether the compound is molecular or ionic.

Forces play a large role in the Big Idea, and it’s clear that student need to be able to differentiate between various strengths of forces and the directionality of those forces.  I’m particularly intrigued here by learning objective 2.3:

“The student is able to use aspects of particulate models (i.e., particle spacing, motion, and forces of attraction) to reason about observed differences between solid and liquid phases and among solid and liquid materials.”

I could see a question such as “Why can you move your hand through air and liquid water but not NaCl.  Justify your answer by discussing the interparticle interactions in each substance.”  Air is a mixture of gas molecules and water is composed of H2O molecules.  In the case of air the interaction between particles are weak dispersion forces, easily overcome by the motion of your hand.  In water the interparticle attraction is still relatively weak hydrogen bonds, but enough that you can feel the viscosity. For solid NaCl however, the particles are much closer together than in air or liquid water and more strongly attracted to one another because each ion is a full +1 charge and they are stacked in a lattice structure.  This means the particles cannot easily move when you wave your hand at them and viola!, it behaves as a solid.

The one part of this Big Idea I am still trying to wrap my head around teaching is LO 2.25 which deals with alloys:

“LO 2.25 The student is able to compare the properties of metal alloys with their constituent elements to determine if an alloy has formed, identify the type of alloy formed, and explain the differences in properties using particulate level reasoning.”

The part of me that studied a little materials science in graduate school feels this is too much for AP/general chemistry level knowledge.  I also don’t have a good way to teach this yet. The key word is yet!  I am going to work on a POGIL activity that addresses alloys, which I will post and discuss on this blog.  Please feel free to bug me if I haven’t done it yet.

Comments, questions, and (polite) arguments are encouraged.  Please leave me a note in the comments below.