Developing Concepts in General Chemistry; Symposium on Chemistry MOOCs

Last week I attended the national ACS meeting in Denver. It was great to catch up with old friends and network with vendors and publishers, but the highlight for me was the symposium at which I presented: Online Courses and the Effect on the On-campus Classroom. Don’t feel like I’m tooting my own horn here, though—there were some amazing folks in the room. The symposium organizer said it best: preparing a MOOC can be a very lonely experience. Even though thousands of people might be watching your videos and hundreds (if you’re lucky) may be posting in course forums, the act of putting the course together is generally a solo venture. To some degree, all of us at the symposium were commiserating with one another.

John Hutchinson‘s talk (from Rice University) was one that stuck out to me. His approach to teaching general chemistry deserves to be spread to all corners of the globe. He emphasized that in addition to bringing education to those who want or need it, MOOCs can act as a vehicle for publishing teaching—not publishing research about teaching, or work in the domain of chemistry, but publishing teaching itself. Naturally, as someone who advocates for the publishing of teaching per se, he’s developed an excellent system for teaching general chemistry through Concept Development Studies.

The idea of the CDS approach is to reveal chemistry concepts in a mostly inductive manner through experimental results. Results of relevant experiments or observations are presented first (say, the gas laws), and a conceptual model is built around these results (say, the kinetic molecular theory of gases), mirroring the way scientific concepts are developed in practice. He argued that most general chemistry is taught backwards, using a deductive model: here are the concepts; now let’s use the concepts to solve deductive problems.

It’s delightful when hearing a speaker rekindles interest in something you haven’t thought about in forever. One of the earliest questions Hutchinson poses in his CDS text is: how do we know atoms exist? He displays an image of a single atom taken with an STM, but then throws a curve ball: the image doesn’t really help us much. After all—and here’s the kicker—to develop the technology to even build the microscope that made the image, we already had to know that atoms exist! The real question is, how do we know atoms exist given only macroscopic observations? That’s where the CDS approach comes in, as he uses mass data to inductively reveal the Laws of Definite and Multiple Proportions.

It’s easy for students and instructors both to take atoms and molecules for granted, but this can be problematic if it means stoichiometry turns into a simple game of dimensional analysis. I also think there’s a good argument to be made that grounding chemical models and theories in data makes them “stickier”—especially when the data runs counter to what we might expect based on a simple model.

Hutchinson has a MOOC through Coursera available here; from the URL, I’m pretty sure it was the first general chemistry MOOC on Coursera. Other online courses/content I’ve checked out since the symposium are Canelas’s Introduction to Chemistry, Sorensen et al.’s Science and Cooking, and John Suchocki’s Conceptual Chemistry. Beautiful production value in the last one, although it seems to be targeted at a lower level.


Percent Yield, Movie Times, and the “Science Unseen”

It’s that time of year again: labs are gearing up. Drawers are being filled with new glassware, students donning lab coats are beginning to fill the halls…the ol’ machine is revving up to roll again. For me, this time of the semester means emphasizing good practices when working up data and results. I’ve written in past semesters about significant figures and some of the interesting issues that come up when teaching them—it’s about the mindset, not the rules, I swear…!

Take percent yield, a measure that has been reported with false precision by countless numbers of students across the generations. Percent yield is really interesting because the balance is one of the most precise instruments that exist in general chemistry laboratories—depending on the range and precision of the balance, measurements with five, six, and even seven significant figures are possible. Thus, it seems like percent yields (which are really just ratios of masses) should in turn have five, six, or seven significant digits. The measured mass of product points to this level of precision.

Students often struggle to understand that the precision of the balance is irrelevant—inevitable variations between runs of the reaction introduce massive uncertainty into yields. Such variations are gargantuan compared to imprecision in balance measurements and essentially render the precision of the balance meaningless. Continue reading →

Writing About Writing About the Second Law

I recently returned from vacationing in the UK, and just spent a couple of days in the West End of Glasgow, near Kelvingrove Park. Yes, the same Kelvin of scientific fame! Seeing his statue got me thinking about the second law of thermodynamics—enough that I was inspired to jot a few thoughts down about the second law.

The second law and entropy are two of the hardest topics to write about at a general chemistry level, in my opinion. Not only has there been fierce debate over the years as to the ideal intuitive notions and analogies for these topics, but related derivations with mathematical rigor can be painfully complicated. There’s a gulf here between the theory and practice of chemical thermodynamics that is difficult to navigate.

A while back I tried just to get down on paper a rigorous derivation of the definition of entropy in terms of heat and temperature, using the second law and a hypothetical thermodynamic cycle. While the work was mathematically correct, the writing made me—the author, mind you!—want to tear my eyeballs out recently. That text will never see the light of day in a general chemistry class. At that point, I wondered if I was even capable of dispensing with rigor to write a more intuitive piece. I’ve always found it difficult to write while sacrificing rigor because I still recall craving rigor and theory in the depths of my soul as a student.

The reality, of course, is that all chemists use heuristics, shortcuts, or metaphors when confronted with certain topics. The best chemist writers can navigate rigorous theory and metaphor with finesse, presenting derivations where the mind “wants” them and metaphors elsewhere. Tro is a good example—while he makes no effort to dumb down important equations, he also presents the practical metaphors that chemists most often use.

In the edition I have, he even manages to lay out all three general interpretations of entropy: entropy as disorder, entropy as energy dispersal, and the statistical interpretation. Color me jealous!

The Elephant in the Water

Just say no to H+...?

Just say no to H+…?

At some point during my personal education in chemistry, I abandoned the use of “H+” to represent “what forms when an acid is placed in water” and switched over to writing “H3O+.” The way I see it, the moment came when my desire to be right and rigorous finally surpassed my urge to be efficient—taking the time to write the extra symbols was suddenly worth the trouble, once I realized that it was apparently a matter of correctness. What one rarely considers as an undergrad is the idea that “H+” wouldn’t have survived to the present day if it didn’t have a kernel of truth to it. What beleaguered chemists hiding out in dark, dusty laboratories are still fighting for the proton? What evidence could possibly bolster these defenders of the proton? Read on!

There is an interesting pedagogical dimension to this whole discussion. Oftentimes when students are learning a new concept or how to solve a new type of problem, functional shortcuts become apparent. These tricks minimize the mental effort associated with problem solving while working with high enough frequency to be tolerable—any trick that works more than 90% of the time is a winner! The catch, of course, is that shortcuts leave out important conceptual details and leave the student’s learning at a disadvantage. As a result, teachers tend to be highly opposed to them while students lap them up. Complicating the situation further, the effectiveness of a particular trick depends on the thoroughness of the teacher and the complexity of assigned problems.

I can’t speak for the broader community, but there was a time when I branded the use of “H+” one of these counterproductive tricks, and I think it’s a fairly common sentiment. For a very wide range of problems, simply writing “H+” works. The nugget of knowledge that the proton is not bare in acidic solutions is very rarely essential to the solution of a problem. Perhaps that fact annoys a lot of teachers—students can get by ignoring it, even though the claim has broader bogus implications (e.g., acids just fall apart in the gas phase, other bare cations can exist in aqueous solution, etc.). The feeling of annoyance encourages the idea in professors that the perpetuation of “H+” is a student-driven conspiracy! Continue reading →

S**t My Undergrads Say

I’m very fond of “ranking problems” that ask students to order a series of compounds in some way and provide an explanation. One of my all-time favorites is the famous “rank these acids from most to least acidic…” problem, which might include compounds like the following.

Rank the compounds shown from most to least acidic. Explain your response.

Rank the compounds shown from most to least acidic. Explain your response.

To really understand a problem like this deeply, the student has to be able to connect the structures provided with either physical/chemical properties or theoretical constructs (such as electron-donating and electron-withdrawing groups). Structure-property relationships are at the root of the appropriate thinking here. Unfortunately, as was pointed out by a recent paper that caught my attention in J. Res. Sci. Teach., students often struggle with structure-property relationships. Without experience under one’s belt, the incredible utility packed into a Lewis structure can be lost on students. It’s staggering, really—what other devices in science approach the information density of a chemical structure?! Continue reading →

Should Hybrid Orbitals Sell the Farm and Move to Florida?

Should hybrid atomic orbitals be placed alongside ancient scientific misconceptions like phlogiston?An interesting controversy has emerged in the Journal of Chemical Education this month, following a paper by Grushow calling for the retirement of the hybrid orbital concept from the chemistry curriculum. The flurry of rebuttals that followed Grushow’s letter are an excellent summary of current thought about the relationship between canonical, delocalized molecular orbitals and localized MOs. The latter, although derived qualitatively from hybrid atomic orbitals, are just as legitimate as the canonical MOs that result from traditional quantum chemical calculations. A wonderful description of the idea with just the right amount of math has been provided by Hilberty, Volatron, and Shaik.

An important point of almost all of the rebuttals is that the traditional photoelectron spectroscopy argument in support of canonical MOs (and arguing against localized MOs) is totally bogus. I mention this particular aspect of the debate because I learned something myself! The traditional argument goes that because methane possesses two different ionization energies, its filled MOs must sit at two different energy levels. The two different ionization energies observed are the result of pulling an electron from MOs of two different energies. Hilberty et al. and DeKock + Strickwerda both point out that localized MO theory may be used with success to explain the two different ionization energies—and that the premises of those who claim otherwise are false. From Hilberty:

The reasoning of those people eager to retire the LMO model, is as follows: since the [Hybrid Atomic Orbital] model puts four electron pairs into four equivalent localized orbitals…then extracting an electron from anyone of these four orbitals should always cost the same energy, leading to a single unique ionization potential (IP). The error in this reasoning is simple: it completely ignores the quantum mechanical requirement that any wave function must match the symmetry of the molecule.

Hilberty goes on to illustrate that when the localized MO approach is applied to this problem, although the filled MOs of CH4 all reside at the same energy, the MOs of ionized CH4+ must bear two different symmetries and sit at two different energies. Hence, two ionization energies should be expected on the localized MO model as well. Continue reading →