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So if we look at its length, it's actually shorter than a single bond, but longer than a double bond.
因此如果我们看它的键长的话，它实际上比单键更短，却比双键更长。
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So, for example, down here I wrote that it was n 2 and that it was h 2, but when I re-wrote the molecules up here, you saw that it's an h h single bond where it's a nitrogen-nitrogen triple bond.
比如，在这下面我写的是氮分子2,而这个是氢分子，但我在上面把这些分子的形式改写了，大家可以看到,这是一个氢与氢之间的单键，含一个氮与氮之间的三键。
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A good example of that is CH4, because the CH bond is polar but symmetrically disposed in space.
甲烷就是一个很好的例子，因为极性键是,空间对称的。
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Well, in '26, the-- i've shorted the one-period bond and so I have to pay out one dollar, but that's exactly what I wanted to do.
6年 我卖空的一年期债券到期了,我需要偿还一美元,不过这恰是我要做的
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But he said the energy of an X-Y bond is going to be equal to the square root.
但他说ＸＹ键的键能,会等于ＸＸ键与ＹＹ键键能乘积的平方根。
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Or if we look at how strong it is, it's actually stronger than a single bond, but weaker than a double bond.
或者如果我们看键的强度的话，它实际上比单键更强，而比双键更弱。
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In valence bond theory, the focus is on discussing the bonds, but it should look very familiar to you, because there's two types of bonds that we want to discuss here.
在价电子成键理论中，所关注的是讨论成键，但这对于你们来说应该很熟悉，因为这是我们要讨论的两种键。
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So, in general what we see, and this is always true if we're comparing the same atom, and in general, if we're comparing different types of molecules, but we know that a single bond is always weaker than a double bond, which is weaker than a triple bond.
通常我们会看到，这对比较相同原子来说总是正确的，通常，如果我们要比较不同种类的分子，但我们知道单键,总是要比双键弱，双键总是要比三键弱。
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As we see a little bit later, I could talk about the carbon-hydrogen bond in methane where there is a plurality of bonds. In this case, there is only the one bond but I just want to get the formulas.
因为我们后来看到一点点，我能讨论甲烷中的碳氢共价键,那有许多共价键，这种情况下，这只有一条共价键,但我想得到氟。
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That's the huge force that we're talking about in terms of making a bond stable, but there are also repulsive forces, so you can imagine we're going to have electron-electron repulsion between the two electrons if we're bringing them closer together.
正是这个非常强的力,使得我们所讨论的这个键能够稳定存在，但是其中还有排斥力存在，大家可以想象一下,我们会有电子与电子之间的排斥力,如果让它们离得更近。
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But once you have a double bond here, we have our pi bond, as well as our sigma bond.
但一旦你有了双键，我们有π键，也有sigma键。
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The housing sector in the United States, you might say, is completely different from municipal bond insurers; but when the housing sector starts going down, people start defaulting on their mortgages.
你可能会说,美国房地产,是与市政债券保险公司完全不同,但是当房地产行业开始衰退,人们就开始对抵押贷款违约
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So, there will be new municipal bond insurers appearing that will take up slack and we'll be all right but the problem is that we may have a crisis for a while.
新的市政债券保险公司将会出现,那样我们暂时可以松口气,但是问题是,次贷危机将会延续相当长的时间
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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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But since in drawing Lewis structures actually, in some cases you do, you can draw a dotted line that means a 1 and 1/2 bond, but most in most cases, we just draw out both resonance structures, and the way that we say it's a resonance structure is that we put it in the brackets and we put an arrow between it.
但是由于在画路易斯结构时,其实，在某些情况下是可以的，你可以画一条虚线来表示一又二分之一键，但是在多数情况下，我们就把两个结构都画出来，而我们说这是一个共振结构的表示的方法是,把它们放在括号里，并在中间放一个双箭头。
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N 2 So any chemist should be able to just look at n 2 and know that it's a triple bond, but that's not something that we've learned how did to do yet, so let's go ahead and start a new topic that's going to allow us to have some sort of sense of what the valence electron configuration, which includes whether something's a single or double or a triple bond can be figured out for any given molecule.
任何一个化学家都应该能够仅仅通过看到2,就知道它有一个三键,但是我们还没学习如何做到这点，因此下面我们就开始进入一个新的主题,它将使我们能够有一定的认识,对于价电子的排布情况，包括可以对任何一个给定分子中的键是单键双键,还是三键作出判断。
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This bond is polar, but again, as I alluded to earlier, because the carbon is centered in the tetrahedron, because of the sp3 hybridization, the molecule itself is symmetric and nonpolar.
这个键是非极性的，但是，我们断言过早，因为C是中心原子，由于sp3杂化，这个分子本身是非极性的且对称的。
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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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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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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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There's not two bonds, that's one pi bond, and the reason is because it's 2 p orbitals coming together, and remember p orbitals have electron density above and below the axis, so when they come together, it kind of looks like one bonds, but essentially what we have here is one pi bond.
这不是两个键，这是一个π键，因为这是两个2p轨道组合而成的，记住p轨道在键轴之上,和键轴之下都有电子密度，当它们靠近时，这看着很像两个键，但本质上它是一个π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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So what actually turns out the reality is that h e 2 does exist, but it exists as the weakest chemical bond known, and it wasn't, in fact, even found to exist until 1993, so I can assure you this is not a bond that you see very often in nature, and it is a very, very weak bond.
实际上He2键是存在的，但它是目前所知的最弱的键，直到1993年它才被发现，所以我可以向你们保证在,自然界你们不可能经常看到它，它是种非常非常弱得键。
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