The question of precisely which elements should be placed in group 3 of the periodic table has been debated from time to time with apparently no resolution. This question has also received a recent impetus from several science news articles following an article in Nature Magazine in which the measurement of the ionization energy of the element lawrencium was reported for the first time. We believe that this question is of considerable importance for chemists and physicists as well as students of these subjects. It is our experience that students are typically puzzled by the fact that published periodic tables show variation in the way that group 3 is displayed. Instructors typically cannot answer questions that students may have on this matter. The aim of this chapter is to make a clear-cut recommendation regarding the membership of group 3, which we believe should consist of the elements scandium, yttrium, lutetium, and lawrencium. Although the arguments in favor of replacing lanthanum and actinium by lutetium and lawrencium are rather persuasive there is a popular and mistaken belief that IUPAC supports the traditional periodic table with lanthanum and actinium in group 3. This view has been disputed by Jeffrey Leigh in an interesting article in which he made it clear that IUPAC has not traditionally taken a view as to the correctness of any version of the periodic table and that there is no such thing as an officially approved IUPAC periodic table. We will briefly review the previous arguments that have been provided in favor of moving lutetium and lawrencium into group 3 of the periodic table in place of lanthanum and actinium. We will then reiterate what we take to be a categorical argument in favor of this placement and will discuss any remaining issues. When added to other arguments made over more than 50 years it becomes clear that the time may have arrived for IUPAC to make a ruling on this question.

depiction of Group 3 In many periodic tables, the f-block is shifted one element to the right, so that lanthanum and actinium become d-block elements in The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). An icon of chemistry, the periodic table is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence Th… The…