If you see a problem that asks you, for example, the third ionization energy versus taking a second electron out of the 2 s in a photoelectron spectroscopy experiment, those are two very different things.

如果你遇到一个题目问你的是，比如说，是第三电离能,还是在光电子能谱实验中从，2，s，轨道中,拿走第二个电子，这可是两个完全不同的问题。

麻省理工公开课 - 化学原理课程节选

You wouldn't be expected to be able to guess that this would happen, because using any kind of simple theory, we would, in fact, predict that this would not be the case, but what we find experimentally is that it's more stable to have half filled d orbital than to have a 4 s 2, and a 3 d 4.

你们不用预期有能力,猜出这个会发生，因为使用任一种简单的理论，我们事实上可以预测不会是那种情况，但是我们在实验中发现的,是半填充d轨道比,4s23d4更加稳定。

麻省理工公开课 - 化学原理课程节选