在这之前我们要引入价电子成键理论，和杂化轨道的概念。

And to do this we're going to introduce valence bond theory, and the idea of hybridization of orbitals.

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这就是成键分子轨道的概念。

So that's the idea of a bonding molecular orbital.

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但记住sigma轨道沿着，键轴方向是没有节点的。

But keep in mind sigma orbitals have no nodal planes along the bond axis.

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So we can think about now doing bonding, and now we have four equal orbitals with one electronic each.

我们现在可以考虑成键了，现在我们有4个等价的轨道，每个上面有1个电子。

麻省理工公开课 - 化学原理课程节选

And what you find is when you have a bonding orbital, the energy decreases compared to the atomic orbitals.

你们发现当你有个成键轨道的时候，相比原子轨道能量要降低。

麻省理工公开课 - 化学原理课程节选

And so this lower level is called a bonding orbital, and it is a bonding molecular orbital.

所以能级较低的轨道叫做成键轨道，这就是成键分子轨道。

麻省理工公开课 - 固态化学导论课程节选