同位素：一种化学元素的两个或多个类型，它们的原子核具有相同的质子数，而中子数却不同。

Isotope: One of two or more species of atoms of a chemical element having nuclei with the same number of protons but different Numbers of neutrons.

youdao

单原子的结构是个基本极限：若要做得更小，基本上就得操控原子核了，这可是把一种化学元素转换为另一种。

A structure the size of an atom represents a fundamental limit: to make anything smaller would require manipulating atomic nuclei—essentially, transmuting one chemical element into another.

youdao

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