OK, then it says draw a single bond from each surrounding atom to the central atom, and subtract two valence electrons.

后将中心原子与其相邻原子之间,连上单键，然后减掉2个价电子。

麻省理工公开课 - 固态化学导论课程节选

So it's trigonal because we have these three atoms that are bound to the central atom here, and if you picture it, it's actually shaped like a pyramid.

这里三角形是因为,我们有3个原子核中心原子成键，如果你画它，它就是金字塔形的。

麻省理工公开课 - 化学原理课程节选

So in terms of the first step of skeletal structure, this is actually going to be easier because we don't have a central atom, we just have carbon and nitrogen here.

对于第一步画出骨架，其实比刚才更容易,因为我们没有一个中心原子，我们这里只有碳和氮两个原子。

麻省理工公开课 - 化学原理课程节选

We were talking about methane, which has only one central atom.

我们讨论的甲烷，只有一个中心原子。

麻省理工公开课 - 化学原理课程节选