On the Placement of Hydrogen and Helium in the Periodic System: A New Approach

Abstract

In this paper the epistemological problem of the rightful position of hydrogen and helium in the periodic system is addressed. We argue for the need of introducing a new approach in order to face this traditional and complex problem. In this sense, we identify the main secondary criteria of classification involved in the discussion and analyze them in conceptual terms. On the basis of this approach, we argue that none of them has explanatory priority over the others when it comes to deciding about the inclusion of hydrogen and helium in a particular family of elements. This implies that the different criteria have the same epistemological status, until we get new arguments or new evidence. As a result, a new table which shows a democratic relationship among the three main secondary criteria of classification proposed is put forth.