It makes a lot of sense when we look at it energetically, because if we think about a 1 s core electron, that's going to be held really, really tightly to the nucleus.

从能量的观点来看这是非常合理的，因为如果我们考虑一下，1，s，芯电子，它会被原子核束缚得非常非常紧。

麻省理工公开课 - 化学原理课程节选