The positions of the elements La, Ac, Lu, and Lr in the WebElements periodic table is justified eloquently in the article by William B. Jensen.1 in J. Chem. Ed..

Elements 117 is not known at the time of writing, but are shown "greyed-out" in the tables at their expected positions for information.

• 1. The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table,
  
  , Journal of Chemical Education, 08/1982, Volume 59, Issue 8, p.634-636, (1982)
  

The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table, , Journal of Chemical Education, 08/1982, Volume 59, Issue 8, p.634-636, (1982)