What’s first?

I am teaching Tutorials in Inorganic Chemistry. Tutorials are 60-90min sessions with 2–4 students where we discuss a topic. Most of this contact time revolves around students’ responses to a problem sheet which I’ve marked beforehand. The purpose of tutorials is quite ambiguous, but seems to be mostly aligned with exam performance.

I am taking over teaching from a few different people, and am finding their approaches to sequencing quite stimulating. The first sequencing question is ‘where should we start?’, and there are two approaches to the first inorganic topic that a Chemistry student does. Some start with effective nuclear charge, while others start with ionic bonding. What should the first Inorganic topic be?

The case for effective nuclear charge

Zeff underpins everything in Inorganic Chemistry. It is the logical fundamental knowledge for developing an advanced understanding of the Periodic Table. Ionic size and charge, bond strengths, orbital mixing, all of the fundamentals rely upon how the valence electrons of an atom behave. Chemists need to master the (annoyingly subtle) patterns of Zeff if they are to understand how Chemistry plays out. The sooner they do this, the better.

The case for ionic bonding

Students know something about ionic bonding already. They understand the NaCl structure. They can reason their way through the relative strengths of NaCl and MgO. Deepening this intuition using the Born-Lande equation and modelling this through to the Kapustinskii equation presents them with a clear challenge to their thinking (using mathematical relationships to understand the interplay of charge and size) while leaving their mental models relatively unchallenged.

Deciding how to begin

Zeff challenges students’ understanding of what Chemistry is. Ionic Bonding challenges students’ understanding of how Chemistry is articulated. Zeff is fiddly and presumably exerts a huge cognitive load upon students. Ionic bonding is more ‘big picture’ and requires students to develop a working knowledge of a few key parameters.

I find the cognitive load argument persuasive in the specific context. Students have enormous non-topic demands upon their cognitive load (these might be non-academic such as socialisation, or might be very academic such as working out how to take notes in a lecture). Starting with material nearer to students’ prior learning seems sensible, as does the neat ‘nuts and bolts’ analysis of the Kapustinskii equation as an introduction into the light mathematicalisation of qualitative Chemical concepts.

Indeed the importance of Zeff might itself make this topic unsuitable for a first tutorial. Zeff needs to be learned deeply – is such learning even possible in the first tutorial? The Problem Solving algorithms of ionic bonding decorate a prior piece of learning; the Problem Solving algorithms of Zeff produce significant conflict with prior learning around stability and ionisation. This conflict takes time and focus (and maybe even self-confidence) to resolve; starting early is probably not as useful as starting well, and starting well is probably best done when the student has clearer expectations of what a tutorial is.

Conclusion

For administrative reasons, I’ll be teaching both sequences to different groups this year. This will present me with some interesting material to reflect upon.

It is not within my power to change the broader course, but it is interesting to think about what the first things in a whole Chemistry degree should be. I wonder sometimes if Organic’s covalent shackles mean that MO theory should be first up. Dealt with as a theme across the subdisciplines, this could help students construct really deep knowledge very early on.