And after the periodic table was developed in the late 1800's, people didn't understand this quite as well, they took things a little more literally.

在十九世纪后期元素周期表经过发展之后，人们还没有很好地意识到这一点，他们的认识还有些粗浅。

麻省理工公开课 - 化学原理课程节选