Inner transition group in periodic table
The block of elements in the periodic table consisting of the lanthanoid series and the actinoid series
The f‐block of the periodic table consists of those elements whose atoms or ions have valence electrons in f‐orbitals. Actual electronic configurations may be slightly different from what is predicted by the Aufbau principle.
F‐block elements are also termed as inner transition elements as they are transition elements within the transition elements i.e., d‐block elements.
Classification of f‐block elements: Depending upon whether the last electron enters a 4f orbital or a 5f orbital, the f‐block elements have been divided into two series:
Lanthanide series (15 elements from lanthanum to lutetium)
Actinide series (15 elements from actinum to lawrencium)
For semantic reasons, the Lanthanides (with the exception of lutetium) and Actinides (with the exception of lawrencium) are shown as two additional rows horizontally below the main periodic table. Otherwise it would stretch too long!
Click for long form of periodic table.