And if we talk about chlorine, and both of the chlorines are the same in this case, we start with a valence number of 7 for chlorine, and then we subtract 6, because it had 6 lone pair electrons around each of the chlorine atoms.

而如果我们讨论氯的话，在这个例子中两个氯的情况都是一样的，从七个价电子开始，然后减去六，因为每个氯原子周围,都有六个孤对电子。

麻省理工公开课 - 化学原理课程节选

And also I wanted to mention in terms of checking your Lewis structures, regardless of what they are, you should always go back and I had 10, and then count 2, 4, 6, 8, 10, because you always need to make sure you have the same number of valence electrons that you calculated in your actual structure.

我还想提一点关于检查,你的路易斯结构的建议，不管它们是什么，你总是应该回去检查一下,我有十个，然后数一数，二，四，六，八，十个，因为你总是需要确保实际价电子的数量,与你在结构中算出的数量相等。

麻省理工公开课 - 化学原理课程节选