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And you can go ahead and tell me what you think the bond order is going to be for this molecule.
你们告诉我你觉得,这个分子的键序应该是怎样的。
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So what I want to point out is that it creates an effect that is exactly opposite of a bond.
我要指出的是,它造成的效果和成键正好相反。
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If I have one that's 400 kilojoules per mole and another that's 200 kilojoules per mole and I blend them, how do I get 500 kilojoules per mole?
如果你有一个每摩尔400千焦的分子,和一个没摩尔200千焦的分子,我把它们并子一起，我怎么得到每摩尔500千焦的键？
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I'm just doing it with a series of switches instead of a fingerboard, which we obviously don't have-- Okay. That's fine. That's great.
只是我用的是阀键,代替圆号上很明显没有的指板,好的,很棒
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The reason it printed that is I accidentally had my finger on the control key, which said print the last thing you had.
这是正确显示的，原因是刚才,我不小心按住ctrl键了，也就是这会显示你最后写的东西。
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There's absolutely no reason I couldn't have switched it around and said that instead the pi orbitals form between these atoms instead of those first atoms I showed.
我完全没有理由,不能把它转过来,现在π键在这些原子间,而不是我开始展示的那些原子间。
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So, if we think about the bonds that are forming -- oh I see our TAs are here, so you can start handing them out, because we have two minutes left to go.
如果我们考虑所成的键-,我看到助教们都来了，你们可以开始发讲义了，我们还有两分钟就下课了。
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Whereas in molecular orbital theory, what I'm telling you is instead we understand that the electrons are spread all over the molecule, they're not just associated with a single atom or a single bond.
而在分子轨道理论里，我要告诉你们的时,我们任为电子分布在整个分子中,它们不仅仅是和,一个原子或者一个键有关。
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And it turns out that when you constructively have two p orbitals interfere, and when I say constructively, I mean they're both either positive or they're both the negative lobes, that's when you got bonding.
当两个ｐ轨道,相长干涉时，我说的相干相长，意思就是说它们要么都是,正的叶瓣要么都是负的叶瓣，这时就能成键。
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And, I know I need to come up with four symmetric equi-length bonds, and let's just see, let's draw the structure here.
我想我们需要,4个对称的等长的键，让我们画出CH4的结构。
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There are nine keys for my left thumb alone so I'm kind of switching between these on the back here and many others, and because of that I can go very high and I'll just demonstrate that.
我的左手拇指就要控制九个音键,通过按动后部,和其他地方的音键,我就能吹出很高的音,我现在就来演示
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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 why don't you tell me what the valence bond description would be of these carbon hydrogen bonds?
你们来告诉我,碳氢键的价,电子是怎样的？
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So what I want to tell you is we also always get the same bond order if we instead only deal with the valence electrons.
我想要说的是我们如果,只考虑价电子也可以得到相同的键序。
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Now I want to ask, what's the nature of the carbon-hydrogen bond?
现在我想问问，碳氢键的本质是什么？
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I'm an organic chemist, so I love carbon, it's one of my favorite atoms to talk about, but it would be nice to get to the point of bonding and even reactions to talk about all the exciting things we can think about once we're at that point.
我是个有机化学家，我喜欢碳原子，这是我最喜欢谈论的原子之一，但我更喜欢讲成键,甚至化学反应的概念,一旦到了这之后,我们就可以考虑各种激动人心的事情。
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By terminal I mean they're only bonded to one thing.
我所说的末端的意思是它们只能与一个原子成键。
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s plus 1s gives you this oval ellipsoid which is the bonding, and here are the antibonding, and then these are the energy levels that I have been drawing for you.
s和1s上两个电子组成的键合电子成椭圆形,这是成键，这是反键电子，这些是刚刚已经画过的能级,我也给你们画了。
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Ok So, according to this model, 90° what we're seeing is a bond angle of 90 degrees.
我听到不同的答案，OK，，I，hear，a，mix。,根据这个模型，我们看到键角是。
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So in the first case of this first bond here that I've put in a square, what type of a bond is this, is the sigma or pi?
在这第一个键里,我用方框把它标出来了，这个键是什么类型的，sigma还是π？
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I have four bonds that are of equal energy, and he called this an sp3 hybrid.
我已经将4个能量相等的键画好了，他把这称为sp3杂化。
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We could also, I think, well, maybe this isn't written out in terms of that convention, which sometimes it's not, so let's also try writing it, such that we have the hydrogen and the oxygen atom there.
我们也可以，我想，好吧，还有可能它不是按照惯例写的，有时候会出现这样的情况，因此，让我们把氢原子和,氧原子成键的情况也写出来。
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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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So any time I draw these molecular orbitals, I do my best, and I'm not always perfect, yet trying to make this energy different exactly the same for the anti-bonding orbital being raised, versus the bonding orbital being lowered.
所以我在画这些分子轨道的时候，虽然不是很完美，但我总是尽量,让反键轨道引起的，能量升高和成键轨道。
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So would you expect this to be a pi bond or a sigma bond her PROFESSOR: OK, so I'm hearing some mixed answers.
你们觉得这是一个π键还是sigma键？,我听到有不同的答案。
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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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So what I want to point out with this case in beryllium is that you don't have to use all of the electrons to figure out the bond order, and in fact, once you get to molecules 10 that are from atoms with atomic numbers of 8 or 10, you're not going to want to maybe draw out the full molecular orbital diagram.
我要指出的是,在Be这种情况下,你不需要利用,所有的电子来指导键序，实际上，一旦分子中,原子序数到达了8或者，你也许不想画出,整个分子轨道图。
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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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