I’m not sure, but there is evidence to suggest that just might be the case.
There’s a nagging irony about the LOs in the new AP Chemistry curriculum when compared to the hopelessly inadequate course descriptions of the legacy exam. It’s something that I’ve been talking about since the inception of the new course, and it’s this; the new LOs ought to provide some significant, specific improvement in terms of informing us about what can (and cannot) be examined, but some potentially odd interpretations of them are worrying. As such, in reality, we won’t REALLY know what each LO specifically means, until we have a decent bank of old (new) exams that help to illustrate the LO’s more completely. This is really the opposite of what the LOs should do, since ambiguity ought to be removed, not introduced, by a more detailed CED!
So, as I continue to think about each LO, I still to get the occasional, worrisome feeling that I’m not really sure about how a particular LO might manifest itself on the exam. However, nothing has (yet) compared to the stunning jolt that I got a few days ago when I posted a fairly innocent question about the 2015 exam, that was answered in a way that I would never have dreamed by Russ Maurer. Here’s what happened.
I posed this question.
At this point we should pause, and examine what Russ is saying.
He’s saying that if a student knows that there are 4 pairs of electrons in total around the O atom, but knows nothing about the 3D nature of molecules and knows nothing about the extra repulsive force of lone pairs, that they would select a bond angle of 90 degrees. We know that a bond angle based upon the traditional, simple understanding of 4 bonding pairs would be approx. 109.5 degrees. Halfway between those two numbers is 100, the lower number of the range accepted.
Russ goes on to ask us to consider the idea that a student might think there were only 3 bonding pairs of electrons around the central atom. In that case the bond angle would be 120 degrees, and halfway between that number and 109.5 degrees (from above), is 115 degrees, the higher number of the range accepted.
Those two situations, taken together Russ argues, would give the range of 100 to 115 degrees. And you know what, he’s right! His analysis does fit with range given as an acceptable answer, but respectfully it is INCREDIBLY esoteric thinking that I think is outside the realm of what I might call ‘normal’ analysis – it works, but it’s a VERY, VERY odd way of thinking about this problem.
It’s compounded of course by the fact that there are NOT 4 bonding pairs around the oxygen atom in ethanol, nor are there 3 bonding pairs around the oxygen atom in ethanol, so using these as markers of some range makes no sense to me.
But even forgetting Russ’ ‘outside of the box’ thinking, why on EARTH would the College Board be OK with the idea that you could go ABOVE a bond angle that could possibly be generated from 4 bonding pairs of electrons around the O atom, i.e., why could you POSSIBLY allow a bond angle above 109.5 degrees? What is even more staggering, is that Russ’ analysis (as he points out), totally ignores the extra repulsive effect of the lone pairs! This is STAGGERING to me.
(Please note that I completely agree with using a range in questions like this, AND I fully understand that bond angles in real molecules offer differ slightly from what simple VSEPR might predict, but this magnitude of range seems bizarre to me, and it appears to abandon a bunch of fundamental principles).
Russ then does a quick analysis of all of the new, released AP questions that deal with VSEPR, and he points out that it appears that no consideration is being given to the extra repulsive power of lone pairs, and that such massive, weird ranges of acceptable answers are effectively removing the need for such knowledge on the new exam! Stunning if true. Stunning. I absolutely defy anyone to read the EK’s or the LOs relating to VSEPR and then reach this conclusion. Russ may well be right, but as I say, there is no way that any sane person would glean this information from the CED – hence my continuing worry.
Even though Russ’ analysis is apparently ‘correct’, it’s highly unlikely that I could bring myself to stop teaching VSEPR in a traditional manner, for two reasons. Firstly I would be far too nervous to accept at this nascent stage that such a modified/diminished treatment is definitive – there’s just not enough evidence from old exams yet. Secondly, I’m not sure that I could abandon the traditional treatment with a clear conscience. If Russ’ analysis proves to be correct in the long term, just WHAT is happening to AP chemistry content here??