Inner Transition Element
An element of the lanthanide or actinide series, in which f orbitals are being filled.
Formula / equation
(n−2)f orbitals filling
Unit
Dimensionless
In depth
Because the filling f orbitals lie beneath two outer shells, these elements vary far less in chemistry than the d-block. Lanthanides are almost uniformly +3, while actinides show a wider range of oxidation states and are all radioactive, with elements beyond uranium made only synthetically.
Examples in the real world
Cerium and neodymium among the lanthanides; thorium, uranium and americium among the actinides.