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与钪和钇一道排在周期表中ⅢB族的应是镧和锕还是镥(最近还有铹)(或用电子述语来说,哪一对元素应作为第6和第7周期中d区的第一个元素)的争论已有相当长的时间,但公布的资料却较少。在相当长的时间内,已经知道钇(在一定程度上包括钪)在化学性质上比起镧来更接近镥及其它较重的稀土金属。为此,本世纪20～30年代期间,一部份化学家认为把镧归于ⅢB族不如把镥归于ⅢB族更为恰当。而建立在结构和差分电子概念基础上的现行周期表,大约是40年代才形成的。 早期对稀土元素的光谱研究表明,这些原子的基态电子结构是〔惰性气体〕(n-2)f~(x-1)(n-1)d~1ns~2。通常认为这符合f—区元素的“理想”电子结构。这样,镱的基态是〔xe〕4f~(13)5d~16s~2,镥的基态是〔xe〕4f~(14)5d~16s~2,这样就导致镥的4f差分电子,于是不容置疑地确定镥是第6周期,f—区的最后一个元素。另一方面,钡的结构是〔xe〕6s~2,镧的结构是〔xe〕5d~16s~2,这样得出了镧的5d差分电子,就把它确定在ⅢB族,作为第6周期,d—区的第一个元素。这种对镧的安排,又通过镧的结构和ⅢB
In combination with scandium and yttrium, the group ⅢB of the periodic table should be lanthanum and actinide or 镥 (more recently 铹) (or, in electronic terms, which pair of elements should be used as zones 6 and 7 in d The first element of the debate has been quite a long time, but the published information is less. It has been known for quite some time that yttrium (to a certain extent including scandium) is chemically closer to lanthanum and other heavier rare earth metals. For this reason, during the 1920s and 1930s, some chemists believed it was more appropriate to assign lanthanum to group IIIB than to group IIB. The current periodic table based on the structure and the concept of differential electronics was formed around the 1940s. Early studies of the spectra of rare earth elements show that the ground state electronic structures of these atoms are [inert gas] (n-2) f ~ (x-1) (n-1) d ~ 1ns ~ 2. This is generally considered to be in line with the “ideal” electronic structure of f-zone elements. Thus, the ground state of ytterbium is [xe] 4f ~ (13) 5d ~ 16s ~ 2, and the ground state of 镥 is [xe] 4f ~ (14) 5d ~ 16s ~ 2, which leads to 4f differential electrons of 镥. To determine 镥 is the sixth cycle, f-zone last element. On the other hand, the structure of barium is [xe] 6s ~ 2 and the structure of lanthanum is [xe] 5d ~ 16s ~ 2. This results in the 5d difference of lanthanum, which is identified in Group IIIB as the sixth cycle , the first element of the d-zone. This arrangement of lanthanum, through the structure of lanthanum and ⅢB