The general electronic configuration of f-block elements is(n−2)f(0−14)(n−1)d(0−1)ns2 General electronic configuration of lanthanoids is [Xe]4f1−145d0−16s2 and actinoides is [Rn]5f−146d0−17s2 So, 4f and 5f orbitals are filled in f-block elements.