Why lanthanides and actinides are kept separately?
The Lanthalides, with atomic numbers 57 to 71, are between Barium and Hafnium. The Actinides, numbers 89 to 103, are between Radium and Rutherfordium. In the layout of the table, the first member of each group (after which the group is named) is in its normal spot. The rest appear as two rows below the last known element - currently Organesson (no 118).
Lanthanides and actinides are under period six and seven eventhough they were part of period six and seven. the best way to find Lanthanides and actinides is to find period six or seven. If you go to Barium or Radium, you will have a line that connects that elements and goes down and leads to a another two lines with names of elements. The top one is Lanthanides and bottom is the actinides.
The lanthanides are in period 6, the actinides in the 7th period. Periods are numbered vertically (down from the top) but run across the periodic table in rows. The columns, sometimes called "groups", are numbered horizontally from left to right but actually run from top to bottom. The lanthanides and actinides are all in column 3, but, because they take up so much room in the periodic table, are placed below it.,