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This is because most fraternities and sororities are named after a series of Greek letters, such as Alpha Delta Pi or Sigma Phi.
VOA: special.2009.09.25
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So we can also name this orbital, and this orbital we're going to call sigma 1 s star.
我们也可以，给这个轨道命名。
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And so it has what? In contrast to the sigma, it has a nodal plane containing both nuclei.
这是什么，和sigma相反，它是包覆在核上的平面电子云，有一个界面。
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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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So it's going to be a sigma bond, 1s and we have oxygen 2 s p 3 and hydrogen 1 s.
它是sigma键，我们有氧2sp3和氢。
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So let's fill it out in this way, 2p keeping in mind that we're going to fill sigma out the pi 2 p's before the sigma.
让我们这样填上去，记住我们先填π,轨道再填。
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sigma 2pz And this is now sigma of 2pz.
现在这是。
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So if we go ahead and name this bond, what we're going to name it is sigma, - because that's the -- basically the shape of the bond or that's how our bond is coming together.
所以如果我们继续并且命名这一键，就是我们要命名的这个键，因为这是-,基本上键的形状,或者这就是键是怎么到一起的。
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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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If we have the molecule ethane, then what we're going to have first is our sigma bond that we described between the two carbons.
如果我们有乙烷分子，那我们首先有,碳碳之间的sigma键。
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sigma STUDENT: Sigma.
学生：
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sigma Here is the sigma.
这就是。
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So z equals 7 -- this is the cut-off where, in fact, the sigma orbital is going to be higher in energy than the pi 2 p orbitals.
所以z等于7-这是分界点，实际上，sigma轨道能量,要比π2p轨道高。
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And again, I want you to have practiced drawing these out in the form you always need to start with the sigma and then write the number of the orbital.
同样的，我希望你们,练习画这种图,你总是要从sigma开始,然后写出轨道数目。
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So this is the 1 s star, sigma 1 s star orbital, and what you have in the center here is a node, right in the center between the two nuclei.
这是1s星，sigma1s星轨道，中间这个是节点，它在两个原子核中间。
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First of all, this is the two s orbitals in hydrogen, 1s plus 1s smearing to give us this sigma molecular orbital.
首先，这是氢气中的两个s轨道，1s与1s轨道重叠,产生sigma分子轨道。
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In contrast, if we have destructive interference, what we're going to form is a sigma 2 s star, and what does the star designate?
相反，如果我们是相消干涉，我们会形成sigma2s星，星代表什么？
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The reason that it's sigma is if you look at the bonding axis here, is that there is no nodal plane along the bonding axis.
它是sigma键的原因是,因为如果你看键轴，上面是没有节面的。
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So when we write that out, we just write sigma 1 s squared, or we can break it up into its individual parts, there's no reason we can't do that as well.
当我们把这个写出来时，我们写sigma1s的平方，或者我们可以把它拆分成每个部分，我们没有理由不能这么做。
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If we have a double bond, we know we need to have only one sigma bond, and we're also going to have one pi bond.
如果我们有双键，我们知道我们需要一个sigma键，还需要一个π键。
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So, as they're very quietly handing out your class notes, let's think about what this bond is here, this boxed bond, is it a pi bond or a sigma bond?
在他们发讲义的同时，我们来看看这个键，方框里的这个键，它是sigma键还是π键？
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So some p orbitals form pi molecular orbitals, and some form sigma p orbitals.
有些p轨道会形成π分子轨道，有些会形成p轨道。
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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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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 it's stigma carbon s p 2, carbon s p 2.
所以它是sigma碳sp2碳sp2。
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In contrast, if we talk about a double bond, what we're now talking about is having both a sigma bond and also one pi bond. And I apologize, I intended to set this up right before class, but that didn't happen today.
相反，如果我们讨论一个双键，我们现在讨论的是,一个sigma键和π键，抱歉，我应该在课前就把这个装好的，今天没装好。
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This will be called lowercase sigma.
用小写的sigma表示。
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And why did I call it a sigma?
为什么我要称他为sigma呢？
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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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