The first one will be above and below the bond axis is where we'll see the electron density, and the second will be perpendicular to that, so it will be a density in front of and behind the bond axis.
第一个是在键轴之上和之下，我们可以看到电子密度，另外一个垂直于它，所以在键轴之前和之后有电子密度。
2
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。
3
And we know that it's electron density between the nuclei that holds two atoms together in a bond.