It is joules per atom. Or, if you multiply by Avogadro's number then you will get joules per mole.

焦耳每个原子，或者，如果乘以,阿伏伽德罗常数你会得到焦耳数每摩尔。

麻省理工公开课 - 固态化学导论课程节选

it's an easy calculation -- we're just taking the negative of the binding energy, again that makes sense, because it's this difference in energy here. So what we get is that the binding energy, when it's negative, the ionization energy is 5 . 4 5 times 10 to the negative 19 joules.

这个计算很简单-我们,只需要取结合能的负值,同样这很容易理解，因为这就是这的能量差,所以我们得到的就是结合能,当它取负值，电离能就是5。45乘以。

麻省理工公开课 - 化学原理课程节选