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And we can actually better visualize this if we plot how that energy changes as a function of internuclear distance.
而我们就能更清楚地看到这些，如果我们画出,能量随核间距的变化曲线。
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So even though we see a nodal plane down the center, I just want to really point out that it's only when we have a nodal plane in the internuclear or the bond axis that we're calling that a pi orbital.
虽然在中间有个节面，我想要指出的是,只有节面在核间轴,或者键轴上时,我们才叫它π轨道。
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If we're talking about a single bond, we're talking about 2 orbitals overlapping in the internuclear axis.
如果我们讨论的是单键，我们讨论的是两个轨道,在核间轴中重叠。
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And a sigma bond forms any time you have two orbitals coming together and interacting on that internuclear axis.
当你把两个轨道合在一起,并在核间轴上有相互作用时,就形成了sigma键。
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Any time two orbitals come straight on together in that internuclear axis, you're going to have a sigma bond.
任何时候两个轨道,在核间轴上直接到一起，你就能得到sigma键。
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Sometimes it's also called the internuclear axis.
有时候它也叫核间轴。
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So, if we look at this graph where what we're charting is the internuclear distance, so the distance between these two hydrogen atoms, as a function of energy, -- what we are going to see is a curve that looks like this -- this is the general curve that you'll see for any covalent bond, and we'll explain where that comes from in a minute.
因此，如果我们来看一看这幅曲线图,这里我们画的横坐标是核间距，也就是这两个氢原子之间的距离，纵坐标是能量，我们看到的这是能量关于核间距的曲线-,这是一条普遍的曲线，在研究任何共价键时你都会遇到，我们马上就会解释一下它是怎么来的。
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When we're talking about r for internuclear distance, we're talking about the distance between two different nuclei in a bond, in a covalent bond.
当我们说，r，代表的是核间距的时候，我们讨论的是一个距离,在一个键--一个共价键的两端的原子核之间的距离。
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And remember for this class, we always define z as the internuclear or the bond axis.
记住在我们的课堂上，我们总是把z方向定义为核间轴的方向。
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A triple bond, again is going to have one sigma bond on the internuclear axis.
一个三键，同样的也有沿着核间轴sigma键。
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The reason that it's a sigma bond is sp3 because the s p 3 hybrid orbital is directly interacting with the 1 s orbital of the hydrogen atom, and that's going to happen on the internuclear axis, they're just coming together.
它是sigma键的原因,是因为,杂化轨道直接和氢原子1s轨道相互作用，它们作用发生在核间轴上，它们会到一起。
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And when I say internuclear distance, we actually call this r here.
而当我说核间距的时候这里，我们其实还是用，r，来表示它。
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All right, so what we see here is we have our sigma bond that's along the internuclear axis here, but we also have a pi bond, because each of these atoms now has electrons in it's in a p orbital, so we're going to overlap of electron density above and below the bond.
这里我们看到sigma键,是沿着核间轴的，但我们还有一个π键，因为每个原子的p轨道上,都有电子，所以电子密度在键的上面,和下面都有电子密度交叠。
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Specifically, it's always the z that forms the sigma orbital, and the reason is at least at a minimum for this class we always define the internuclear axis as the z axis, so this is always the z axis, so it's always going to be the 2 p z's that are coming together head-on.
特别的，z总是形成sigma轨道，这是因为至少在这个课里面,我们总是定义核间轴为z轴，所以这总是z轴，所以2pz轨道总是,朝一个方向出现。
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