Atoms consist of an atomic nucleus surrounded by a cloud of electrons.

每个原子都由原子核，以及围绕它的电子云组成。

If this were a nucleus, then the cloud of electrons would stretch out to something like a kilometre away.

假如这是一个原子核的话，那么电子的运转范围可以延伸到一公里之外。

That’s where a cloud of electrons shifts to one side of a molecule, creating a negative charge on one end, and a positive charge on the other.

这就是电子云转移到分子一侧的地方，在一端产生负电荷， 在另一端产生正电荷。