So let's do a quick clicker question, and you tell me how many valence electrons does fluorine have? Remember, valence electrons are different from core, they're only the outer-most electrons in the outer-most shell.

那么让我们来做一个小选择题，请大家来告诉我,氟有多少个价电子，要记得，价电子与芯电子不同，它们是在最外壳层的最靠外面的电子。

麻省理工公开课 - 化学原理课程节选

So what I want to point out when you're kind of looking at these numbers here, what the significance is, look at that huge difference between what the ionization energies are for what we call those valence electrons, -- those outer shell electrons, those are core electrons there.

我在这里想要指出的是,当大家在看这些数字的时候，最重要的是，要看到这些,巨大的差异,看到所谓价电子，即外层电子的电离能与，1，s，轨道，电离能之间的巨大差异。

麻省理工公开课 - 化学原理课程节选