关于是镧和锕或是镥和铹应同钪和钇在一起,或者说,哪一个应是第六、七周期 d 组的第一个成员的争论已有很长的历史了,虽然这种争论很少公布。由于众所周知的钪和钇在它们的化学性质上接近于镥和重希土的理由,所以在本世纪20和30年代,大多数化学家都把镥而不是把镧放到ⅢB族。把镧和锕放在ⅢB族只是在40年代后由于以电子排布和有可区别的电子的概念为基础的周期表的使用之后而发展起来的事情。早期的希土元素的光谱学工作表明,除少数例外,它们的原子的基态电子排布形式 The controversy over whether or not 镥 and 镥 and 镥 and 铹 should be associated with one another, or which one should be the first member of group d and the sixth cycle, has a long history, although Arguments are rarely announced. Because the well-known plutonium and plutonium are similar in their chemical properties to those of plutonium and earth, in the 20th and 30th centuries this century, most chemists put plutonium instead of plutonium into the group IIIB. Putting 镧 and 锕 into the group IIIB was only developed after the use of the periodic table based on the concept of electronic arrangement and distinguishable electronics in the 1940s. The early work of spectroscopy of rare earth elements showed that, with a few exceptions, the ground state electronic arrangement of their atoms