So if we take a look at nitrogen here, what you'll notice is we have thre available for bonding, - and we already have our lone pair -- one of our orbitals is already filled up.

如果我们看一下氮原子，我们注意到我们可以成3个键，我们已经有一个孤对-,其中的一个轨道已经被填满了。

麻省理工公开课 - 化学原理课程节选