Elements in the first column all have one electron in their outermost shell. Those in the second column have two outer electrons, and so on.

第一列元素最外电子层内均有一个电子，第二列元素则含有两个电子，依此类推。

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So there are two electron configurations in the n equals one shell, if we follow according to the selection rules that we spelled out last day.

如果根据上次课,我们阐明的原子光谱选择定则，我们就会知道在n等于1的那一层,有两种电子图像构型。

麻省理工公开课 - 固态化学导论课程节选