Teachers can know too much

High School chemistry rests on a base of sophisticated quantum mechanics.  Fortunately, it’s not necessary to master the advanced subject in order to use its results.

Our tutoring consultant was recently notified that a High School student needed particular help in the subject of chemistry, and was given a stack of handouts and homework problems from that class.  He hadn’t done anything with those parts of the subject for a long time, so he pulled out some of his old textbooks to remind himself of the important points.

He was initially amazed that students in secondary school were expected to learn these things.  Atomic structure is based on quantum mechanics, mathematically sophisticated and often bizarre (which means your intuition gives the wrong answers).  How can a student who has never seen calculus be expected to work out the selection rules for electric dipole transitions?

Of course they aren’t expected to do anything of the sort.  That happens to advanced college students majoring in physics, not average High School students.  Our consultant was handicapped by the fact that he knew too much about the subject, and so pictured it as a very advanced thing indeed.  After a moment, he put back most of his textbooks and concentrated on a simpler version.

Much of chemistry does not really need a sophisticated version of quantum mechanics.  Sometimes just a ball-and-stick picture of a molecule is enough; often a set of empirical rules is quite sufficient as a guide.  In any case, the situations simple enough to allow ab initio calculations are really rather few.  To say that chemistry as a whole is mostly a set of empirical rules is, at best, an enormous oversimplification.  But there are unkind physicists who will say it (though generally not out loud when visiting the Chemistry Department.

It’s not true, though, that having a more extensive background in a subject is always a handicap.  In fact it’s often very helpful to know where some of the results actually come from, to put them in context and to be able to know just how much of a simplification is being made.  The hard part is to put together an explanation at a simpler level that is at once understandable, consistent and does no violence to more sophisticated truths.  That sort of skill is not guaranteed by one’s own understanding.  One can be a good scientist but a poor teacher.

And one can be a great teacher without being an outstanding scientist.  Our consultant can name several.  Can you?