So hopefully, it was a time issue in terms of looking at the periodic table, because let's have you tell me what are we looking for here?

希望刚才大家出问题的原因,是因为看周期表有时间限制，请大家告诉我,我们在这里找什么？

麻省理工公开课 - 化学原理课程节选

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