The periodic table is an icon. But chemists still can’t agree on how to arrange it New data about the elements and their relationships have led to debate over the 150-year-old table’s optimum ...

f-block elements Actinides and lanthanides, the f-block elements, are used in a wide variety of fields including telecommunications, medicine, imaging, sensors, energy, catalysis, and data storage.

To account for this, most periodic tables hive off the elements making up this f-block, putting it below the table, leaving a gap in group 3. Fair enough.