Formal charge is something that I’ve written about in an AP context on more than one previous occasion, and you can read those posts here and here. This week, formal charge came up in conversation once more, and in the course of that discussion, something else caught me eye.
Formal charge is definitely part of the Essential Knowledge statements in the AP chemistry curriculum (see EKC4d on pages 30 and 31 here) but for me, there’s something troubling about what’s written there. Although FC is obviously mentioned, it’s really difficult for me to see precisely how it could be asked in the context of the only LO that goes with EK2C4! The relevant LO is 2.21 that states;
“The student is able to use Lewis diagrams and VSEPR to predict the geometry of molecules, identify hybridization, and make predictions about polarity.”
I suppose if you consider formal charge to be part of ‘Lewis Diagrams’, or if you consider that the choice of one structure over another via formal charge will lead to one type of hybridization/polarity being chosen over another, then this could be a connection of formal charge to LO 2.21, but to me, that all seems TERRIBLY convoluted. A more feasible conclusion (at least to me), is that the College Board has created a document that includes a reference in the EK statements that can never actually be asked on an exam, since it doesn’t jive with the only, equivalent LO! (Remember, all exam questions have to be tied to a LO).
BTW – this is not a debate about whether one should teach FC or not, rather my (first) question is this; Is anyone convinced that LO 2.21 could be twisted to include a question about FC?
If not LO 2.21, then is there another LO that could be twisted in such a way?
If the answer to the second question is ‘yes’, then does this start an interesting precedent where LO’s that are formally tied to certain sets of EK statements in the curriculum document, could actually be tied to OTHER sets of EK statements?
Finally, if the answer to the second question is ‘no’, then do you agree that FC is not actually examinable since all questions must be aligned with a LO!?