The period of table's on the back page of your notes if you don't see that there.

元素周期表在你们讲义的封底,如果你没看到的话。

麻省理工公开课 - 化学原理课程节选

So, for example, we can move to the next periods in the periodic table. When we talk about a period, we're just talking about that principle quantum number, so period 2 means that we're talking about starting with the 2 s orbitals, period 3 starts with, what we're now filling into the 3 s orbitals here.

我们可以移至周期表的下一个周期,当我们讨论一个周期时，我们仅仅讨论,周期3以我们所填充的3s轨道，开始填充所以周期2意味着,我们从2s轨道谈起，周期3以我们所填充的3s轨道开始填充。

麻省理工公开课 - 化学原理课程节选