It covers GCSE concept of electron shells compared to sub-levels, orbitals, rules for filling, short hand configurations and deciding on the blocks in the periodic table. (tes.com)
Moreover, if these photons are to have a chance of reaching the inner electron shells, they must have energies in the upper end of the extreme ultraviolet (XUV) spectrum. (sciencedaily.com)
All lanthanides except lutetium are f - block elements, corresponding to the filling of the 4f electron shell. (sciencedaily.com)