It makes sense, right, because they're the furthest away from the nucleus, they're the ones that are most willing to be involved in some chemistry or in some bonding, or those are the orbitals that are most likely to accept an electron from another atom, for example. So the valence electrons, those are the exciting ones.

它讲得通，对，因为它们距离,原子核最远，它们是最容易发生,化学反应和结合的地方，另一个原子的电子的轨道或者它们是,最容易接受，举个例子所以价电子，他们是活跃的电子。

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