自习课上，学生A和学生B在复习讨论关于元素的问题。学生A对于元素的概念，我还不太理解，你给我讲讲好吗？学生B书上不是写得很清楚：“元素是具有相同核电荷数的一类原子的总称”。学生A我知道这个定义，但我还不完全理解。比如说，既然是“一类原子的总称”，为什么不总称为 In the self-study class, Student A and Student B are reviewing and discussing about the elements. Student A’s concept of the element, I do not understand, do you speak to me? Student B’s book is not very clear: “Elements are a generic term for a class of atoms with the same nuclear charge.” Student A I know this definition, but I don’t fully understand it. For example, since it is a general term for a class of atoms, why is it not always called