While Lanthanum itself isn't technically part of the "inner transition series" (which consists of the Lanthanides and Actinides), it's often grouped with them due to its similar chemical properties.
Here's why:
* Lanthanides: The elements with atomic numbers 58-71 (Cerium to Lutetium) are considered the "inner transition" metals, as they have their last electrons added to the 4f subshell.
* Actinides: The elements with atomic numbers 90-103 (Thorium to Lawrencium) are also inner transition metals, with their last electrons added to the 5f subshell.
Lanthanum, despite having its last electron in the 5d subshell, behaves similarly to the Lanthanides and is often included in discussions of inner transition metals.
