Electron Configurations of the Lanthanides and f Orbitals

The lanthanides (and actinides) are those in which the 4f (and 5f) orbitals are gradually filled. At lanthanum, the 5d subshell is lower in energy than 4f, so lanthanum has the electron configuration [Xe] 6s 5d (Table 2.1). 

Lanthanide and Actinide Chemistry 2006 John Wiley Sons, Ltd. 

The radial part of the hydrogenic wave functions for the 4f, 5d and 6s orbitals of cerium (after H.G. Friedman et at. J. Chem. Educ. 1964,41, 357). Reproduced by permission of the American Chemical Society (c) 1964. 

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