So, for example, if I have a sodium ion over here, and I have a chloride ion over here, where the distance from center to center r I'm denoting as r, this is nucleus to nucleus separation.

所以，比如这有一个钠离子，和一个氯离子，它们中心与中心间的距离,我把它设为，这是原子核和原子和的间距。

麻省理工公开课 - 固态化学导论课程节选

r+ And let's say that sodium has a radius, r plus, r- and chlorine has a radius, r minus, when r is very large in comparison to the radii of the ions, I don't need to draw them this way.

让我们假设钠有半径，是，氯也有半径，是，当r比离子半径大很多的时候，我不需要这样来描述。

麻省理工公开课 - 固态化学导论课程节选