Confusing Electron Fields

Recently, an xkcd comic address the standard explanation of how a wing works:

It instantly made me think of an experience I had in my sophomore chemistry class in high school. We were discussing the layout of electrons. Specifically, my teacher was presenting the order in which shells and subshells are filled. The order is really interesting because you don’t fill an entire shell before moving onto the next. You get a pattern like this:

The vertical axis shows the different shells, starting with the lowest level at the top and working downward. Subshells are on the horizontal, moving from low on the left and moving to the right. The arrows show the order in which the subshells are filled.

The idea that you would fill subshell s on the 4rd shell before d on the 3rd really interested me. Especially because that pattern continues throughout the array. So I asked my teacher to explain why it was like that. My teacher’s response? Terribly similar to option two in the comic above:

The explanation will only confuse the other students, so we won’t talk about it.

What a dismissive attitude. Is not the point of learning to understand why? Simple rote memorization of an electron arrangement isn’t really learning. True learning encompasses the entire system. The “why” is as critical as the “how.” In that spirit, here is the “why.”

When the separation between the orbitals is small, it requires less energy to put electrons into the higher energy shell than it is to put two into the same low-energy shell. This is because of the repulsion resulting from matching two electrons in the same shell. Once the first higher subshell is filled, adding another would take more energy than the lower level subshell, thus electrons return to filling the lower shell. Thus the pattern shown above is formed. The rules of electron arrangement are known as the Aufbaur principle.

This concept might have been too complex for some of my classmates. But it was not so complex that no one would have understood it. In fact, the explanation might have actually helped us remember how to apply Aufbaur principle when filling out electron arrangements. We would gained real knowledge, rather than simple memorization.

But it wasn’t going to be on the test. If it wasn’t the test, we didn’t need to learn it. If we didn’t need to learn it, my teacher wasn’t going to teach it. No need to waste the effort to teach something students “didn’t need.”

-That is all.

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