I am now getting into the nitty-gritty of the new curriculum as I prepare my materials for a huge overhaul and re-write.
In general, exclusion statements are incredibly useful, and frankly should ALWAYS have been in the course description, BUT until we see further sample questions, and/or we have a history of the new exam, some guesswork remains necessary. Here are my thoughts on the exclusion statements, and their potential consequences, as they stand now.
- Memorization of exceptions to the Aufbau principle – it hardly seemed like a burden to simply mention Cr and Cu, so this isn’t a major change, but I am grateful that there is now a specific statement of what is (and isn’t needed). I will no longer refer to the exceptions.
- Assignment of quantum numbers to electrons – simple fix; stop teaching quantum numbers. A shame, I like the logic of them.
- Phase diagrams – I know that people are upset about this, but frankly I have no strong feelings. ‘In’ or ‘out’, I can cope.
- Colligative properties – For me, as per phase diagrams, above. Simply remove them.
- Calculations of molality, percent by mass and percent by volume – see colligative properties, above. Remove.
- Knowledge of specific types of crystal structures – this confuses me. I have NEVER taught kids about packing, FCC, BCC or any type different, crystal structures because it has never been asked on a contemporary exam (unless embedded in a MCQ that we don’t see). As such, this has always been excluded by me! It may be for the benefit of those teachers that insist on using the textbook as a guide as to what to teach – that’s not me, that’s not me, so no change.
- The use of formal charge to explain why certain molecules do not obey the octet rule – interesting. I do NOT interpret this to mean that formal charge will not be tested, but rather I take a literal view that it would not be used in to explain non-octet situations. My reading of that statement suggests that it could be used in distinguishing between two structure that DO obey the octet rule. Either way, I’m still going to teach formal charge until someone gives me a different, official interpretation of the statement.
- Learning how to defend Lewis models based upon assumptions about the limitations of the models – Errr…what? I don’t think that I understand what this is talking about! It seems to be linked to Essential knowledge 2.C.4.f, and I suppose it might mean that they will never ask about Lewis structures with odd numbers of electrons, but to be honest I’m not at all sure. Either way, I suspect the impact upon my teaching here is minimal (unless I find differently when it has been explained to me!)
- An understanding of the derivation and depiction of these (hybrid) orbitals – a couple of interesting things here. Who on earth has been getting into ‘derivation and depiction’ of hybrid orbitals, anyway?? Secondly, since the statement goes on to explicitly say that sp, sp2 and sp3 are still in play, and that any ‘d’ hybridization is out, then I will simply trim my references.
- Other aspects of molecular orbital theory, such as recall or filling of molecular orbital diagrams – well, like crystal structures I have never taught any MO since it has been off the table for years, so that’s one angle. The other angle is that 2.C.2.i, suggests that questions could be asked about the interpretation of an MO diagram. This is an interesting development, and is one area that I am VERY anxious to see example questions on. I’ll be looking into what this means a little more.
- The study of the specific varieties of crystal lattices for ionic compounds – isn’t this the same as the sixth point, above?
- Lewis acid-base concepts – Hmmm, this seems to be wrong to me. There are so many Lewis acid/base applications outside of simply ‘acid-base’ (like ligands bonding in complexes for example) that are useful to teach, I will be leaving this IN my course.
- Language of reducing agent and oxidizing agent – this is NUTS. I suspect that the motivation is ‘it’s just too hard for the kids, the poor things can’t cope with the complicated words!’. Tough. If you can’t ‘get’ this, then you are just not cut out to be doing ANY chemistry let alone AP. This exclusion makes zero sense.
- Labeling an electrode as positive or negative – I’m happy about this, since the arbitrary way this is done in electrolysis and electrochemical cells is confusing and not especially relevant to understanding the electrochemistry itself. I suppose one could apply the same argument to oxidizing and reducing agents and therefore call me a hypocrite, but I have a gut feeling that most chemistry teachers would see the difference between my two positions (and agree with me).
- The Nernst equation – no strong feelings here, I’ll just chop it out.
- Calculations involving the Arrhenius equation – as an exclusion, this is a bit of a red-herring since calculations have hardly ever been asked in a contemporary exam. Really, the only useful application of the equation is in a, y = mx + b plot to determine the activation energy, so not a ‘calculation’ as such. I will continue to include it in that context and continue to exclude complicated, Arrhenius calculations from my course. No change here for me.
- Collection of data pertaining to 4.C.3b – another red-herring. Who the heck has been ‘collecting data’ to build evidence in support of one reaction mechanism over an alternative??
- Numerical computation of the concentration of each species present in the titration curve for polyprotic acids – OK, fair enough, it’s a pretty uncommon question, anyway.
- Computing the change in pH resulting from the addition of an acid or base to a buffer – I think it is still entirely possible that a calculation using HH in a titration, could be on the table. I interpret that statement to mean that a question where a buffer is formed outside of the context of a titration, and then some EXTERNAL addition of acid or base occurs, is ‘out’. See 1993, 1(c) for exactly the kind of thing that I am talking about. Having said that, I would always offer a caveat. Until we have a sample exam, and/or a history of old exam questions, any interpretation (unless qualified by the CB) will involve some level of conjecture and uncertainty. i.e., I reserve the right to change my mind!
- The production of the Henderson-Hasselbalch equation by the algebraic manipulation of the relevant equilibrium constant expression – Errr?? Who is doing that anyway, when the HH equation is ALREADY ON THE DATA PACKET!!
- Memorization of other ‘solubility rules’ – It’s a pity, since some rote learning is good for kids. Also, competent chemists do NOT have to ‘Google’ every, single piece of factual information!
- Computations of solubility as a function of pH – it would appear that this exclusion statement, and the final one (below), are both saying that quantitative, common ion calculations, that involve H+(H3O+) or OH– are off the table. I think that one could also interpret them to mean that ALL, quantitative common ion treatments are ‘out’. IF that is the case, then it would have been clearer to move the second exclusion statement from p 71, to sit directly underneath 6.C.3e on p 70, rather than in the position it currently occupies.
- Computations of solubility in such solutions – see previous.
Of course, these are only opinions, and as I have said on several occasions, involve a degree of guesswork on my part, so let’s hear some other points of view.