这就是成键分子轨道的概念。
第六步是想一想我们有多少个成键电子剩下？
Step six is thinking about do we have any bonding electrons left?
价电子成键理论，非常容易理解。
So the idea behind valence bond theory is very easy to understand.
我们从成键中获得。
这是成键和反键。
让我们用价电子成键理论来看一看甲烷。
显然，没成键是最弱的。
And obviously, no bond is the weakest of all is not bonding.
这是当我们有3个成键电子，和一个孤对时这样称它。
That's what we call when we have three bonding atoms and one lone pair.
本质上，它只能允许我们,和两个氢原子成键。
Essentially it would only allow for us to bond to two hydrogen atoms.
这是反键分子轨道，我们有了成键，现在我们讨论反键。
So if we name this orbital, this is an anti-bonding molecular orbital So we had bonding and now we're talking about anti-bonding.
本质上就是由于，未配对电子配对导致的成键。
Essentially what you have is bonds resulting from the pairing of unpaired electrons.
你应该了解考虑成键时，去考虑内层电子，是毫无意义的。
You can see that there is no value in studying inner shell electrons to ask questions about bonding.
我们看到3对成键电子所以这是一个三重键，它确实是多重键。
We see three bonding pairs so this is a triple bond, indeed a multiple bond.
在成键时，会释放大量能量，这比补偿激发电子，的能量要多。
We're going to release a lot of energy for bonding, it's going to more than make up for the fact that we actually had to spend some energy to promote that electron.
我们现在可以考虑，怎么在价电子成键理论中描述这个键。
So, we can think about now how do we describe this bond in valence bond theory.
所以能级较低的轨道叫做成键轨道，这就是成键分子轨道。
And so this lower level is called a bonding orbital, and it is a bonding molecular orbital.
在这之前我们要引入价电子成键理论，和杂化轨道的概念。
And to do this we're going to introduce valence bond theory, and the idea of hybridization of orbitals.
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。
So any time you have two atoms bonding, the bond axis is just the axis that they're bonding along.
那么我们有十八个电子，下一步要做的是判断,我们有多少个成键电子。
So we have 18 electrons, and the next thing that we need to figure out is how many bonding electrons we have.
记住，这在我们讨论到，成键的时候很重要，现在你们还不用太多的考虑它。
Remember, that's going to become important when we talk about bonding, we don't need to worry about it too much right now.
体温下聚合物和水之间的化学键变弱，聚合物分子彼此更易于成键。
At body temperature, the polymer-water bonds weaken, and the polymer molecules prefer to bond with each other.
但是，在周五我们,会用一种新的办法来讨论,不止两个原子的分子的成键。
However, on Friday we will use a different approach so we can talkabout bonding within atoms that have more than two atoms, molecules with more than two atoms.
我们知道是两个原子核之间的，电子密度保持两个原子在一起成键的。
And we know that it's electron density between the nuclei that holds two atoms together in a bond.
我们现在可以考虑成键了，现在我们有4个等价的轨道，每个上面有1个电子。
So we can think about now doing bonding, and now we have four equal orbitals with one electronic each.
因为我们有一对，在2s轨道里已经配对了，所以只剩下两个电子可以用来成键。
Because we have paired set in a 2 s orbital, so all we're left essentially is two electrons that are available for bonding.
目前为止任何时候我们尝试要，描述分子内的成键，我们都是利用Lewis结构。
So far we've exclusively been using Lewis structures any time we've tried to describe bonding within molecules.
我们还有6个地方可以供氢原子成键，我们可以继续把这些电子填充进去。
We also have six spots available to form hydrogen bonds, so we can go ahead and fill in those electrons as well.
因为第五步要做的是将我们的成键电子填在这，所以我们开始在每个键处填上两个电子。
Because step five is that we need to fill in our bonding electrons, and we start it with filling in two electrons per bond.
因此你能看到,反键轨道上有两组，三组成键，得到一组净成键，所以成的是单键。
so you can see that there is going to be two sets in antibonding, three sets in bonding for a net of one, giving us the single bond.
如果我们考虑有六个氢原子，每个都会合起来，碳杂化轨道成键，每个氢的1s轨道。
And if we think about the six hydrogens, now each of those are going to bind by combining one of the carbon hybrid orbitals to a 1 s orbital of hydrogen.
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