And if all of the possible brackets were filled out on standard paper and stacked on top of each other, how big would the pile be?" It would actually go from the earth to the moon and back,1.1 million times,".

VOA: standard.2009.03.25

I don't care how you do it on exams or on problem sets, but you do need to be aware that the 3 d once filled is lower in energy than the 4 s, and the reason you need to be aware of that is if you're asked for the electron configuration now of the titanium ion.

我不关心你们在考试或者,问题集中如何做它，但是你们的确需要知道3d一旦被填充,它的能量是小于4s的，你们需要知道这个的原因,是如果你现在被要求,写出钛离子的电子构型。

麻省理工公开课 - 化学原理课程节选