These 2 are going to come together like this, and the first bond that we're going to form is going to be a sigma bond, right, so we see that here. If we're looking head on, we see they form a sigma bond.

它们两个会靠近到一起，首先会形成的是,一个sigma键，对吧，我们在这里可以看出来，我们看到它们形成一个sigma键。

麻省理工公开课 - 化学原理课程节选