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。

麻省理工公开课 - 化学原理课程节选

px So we're talking about pi carbon 2 p x, 2px because it's the x axes combining to carbon 2 p x.

我们讨论的是π碳，因为它在x轴结合成碳。

麻省理工公开课 - 化学原理课程节选

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, if we think about this z bonding axis between the two carbon atoms, we can picture overlap of those s p hybrid orbitals, and then we can also picture bonding to hydrogen.

如果我们考虑,两个碳原子之间的z成键轴，我们可以画出sp杂化轨道的交叠，我们也可以画出和氢原子的成键。

麻省理工公开课 - 化学原理课程节选

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。

麻省理工公开课 - 化学原理课程节选

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。

麻省理工公开课 - 化学原理课程节选