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So any time you have two atoms bonding, the bond axis is just the axis that they're bonding along.
任何时候如果你有两个原子成键，键轴就是它们成键的方向。
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Remember this is our bond axis here, and you can see there is this area where the wave function is equal to zero all along that plane, that's a nodal plane.
记住这是我们的键轴，你可以看到在这些区域,波函数在这个面内全都是零，这是节点面。
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And the convention is that when two atoms bond, they bond along the z-axis.
我们的惯例是，两个轨道成键，键轴为Z轴。
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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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So it's very important to be keeping in mind that any time you see a double bond, you have a pi bond there, so you're not going to see any rotation around the bond axis.
所以你们要记住,任何时候你们看到一个双键，这里面有π键，你们不会看到关于键轴的任何转动。
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Pi orbitals are a molecular orbital that have a nodal plane through the bond axis.
轨道是沿着键轴,有节面的分子轨道。
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So that is the bond axis it's just the axis between the two nuclei.
这就是键轴,它就是两个原子核之间的轴。
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So it's along the bond axis and it's between a carbon s p 2 hybrid, and then the hydrogen is just a 1 s orbital that we're combining here.
所以它是沿着键轴方向的,而且这里是一个碳sp2杂化轨道，和一个氢的1s轨道的结合,在这里我们可以合并他们。
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But in sigma orbitals, you have no nodal planes along the bond axis, so if we had a nodal plane here, we'd see an area where the wave function was equal to zero.
但在sigma轨道里，沿着轴向是没有节点平面的，如果我们有个节点，我们就会看到某个地方波函数等于0。
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So in terms of the carbon hydrogen bond, it's a sigma bond, - because we define it -- any time we are bonding to an atom, we have to keep redefining our bond axis to whatever two atoms we're talking about.
对于碳氢键，它是sigma键，因为我们定义它-,任何时候我们有原子成键，我们要重新定义键轴方向,为我们所讨论的两个原子方向。
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But keep in mind sigma orbitals have no nodal planes along the bond axis.
但记住sigma轨道沿着,键轴方向是没有节点的。
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So again, we can name these molecular orbitals and these we're going to call also to point out there is now a bond axis along this nodal plane, which is something we didn't see before when we were combining the s orbitals.
同样的，我们可以,命名这些分子轨道,这些轨道叫做-同样要指出的是,现在沿着键轴是一个节点面，这是我们讨论s轨道的时候,从没有看到过的。
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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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If we think about that, that's a sigma bond, right, they're coming together along the nuclear axis.
如果我们考虑它的话，它是sigma键，对吧，它们沿着核轴方向靠近。
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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 first one will be above and below the bond axis is where we'll see the electron density, and the second will be perpendicular to that, so it will be a density in front of and behind the bond axis.
第一个是在键轴之上和之下,我们可以看到电子密度，另外一个垂直于它，所以在键轴之前和之后有电子密度。
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We're having two orbitals coming together on the bond axis.
我们在这个轴上有两个轨道相互靠近。
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So pi bonds have electron density both above and below the bond axis, but they actually have a nodal plane at this z, this bond axis here.
键在键轴之上,和之下都有电子密度，但它们在z方向有节面，这是键轴的地方。
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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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Now let's think about this first pi bond, which will be above and below the bonding axis.
让我们先来看这个π键，它在键轴的上面和下面。
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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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If we have, coming along this z axis, another carbon atom, we can actually form one bond between the two carbon atoms there.
如果我们在z方向，有另外一个碳原子，我们可以在,两个碳原子之间形成一个键。
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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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