A Very Special Place in the Periodic Table

In group 3, we find scandium, Sc, yttrium, Y, and lanthanumm. La, the latter with atomic number 57. One step to the right we expect to find the atomic number 58. But instead there is number 72, Hf. 14 elements are missing This chapter is devoted to the exciting story of discovery and discoverers, and descriptions of the modern uses of these high-tech elements Sc, Y, La and lanthanides. 

The two outer electron shells in neutral atoms of each lanthanide element have the same number of valence electrons as lanthanum, 2 and 1 respectively. This is the reason for the great similarities between them. And this is also the background to the enormously difficult discovery and separation work, characteristic of the lanthanides. But there are in fact some differences. In the third shell, the numbers of the so-called f-electrons differ. Lanthanum itself has no f-electron, the first lanthanide, cerium Ce, has 1, the second, praseodymium Pr, has 2 and the fourteenth, lutetium Lu, has 14 (see below, section 17.5.1). 

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