Question

Write general electronic configuration of lanthanide series elements.

Answer 1

The f-block elements are the Lanthanides and Actinides,also known as the inner transition elements. They are placed separately below at the bottom the periodic table as an ‘island of elements’. There are two speculations as to why they are placed where they are, the first being that they have not been completely studied hence the separation and the second reason being that it just looks aesthetically pleasing to have a more condensed periodic table!

The general electronic configuration of Lanthanides is [Xe] 4f^(1–14) 5d^1 6s^2 and for Actinides it is [Rn] 5f^(1-14 ) 6d^0-1 7s^2

The reason why these elements are based off Xenon and Radon is due to the fact that the f-block does not actually exist as an ‘island’ but in fact it is embedded inside the d-block (so I’ve moved the elements in how they should actually be arranged for clarity).


The lanthanide series includes elements from number 58 to 71, which is 14 elements. The f sub-level contains seven orbitals and each orbital will hold two electrons. Therefore, it is possible to place 14 electrons in the 4f sub-level. Generally speaking, the lanthanides have electron configurations that follow the Aufbau principle.

The lanthanide series fills the 4f sub-level as you move from cerium (Ce) to lutetium (Lu). The same holds for the actinide series that runs from atomic number 90 through to number 103, again 14 elements. Thus, as you move from thorium (Th) at element number 90, you begin to fill up the 5f sub-level and continue to fill up the 5f sub-level until you finish the actinide series at lawrencium (Lr).