Brigitte Van Tiggelen

After 150 years of scientific developments, the periodic system of chemical elements is still an icon of modern science. Its resilience is striking. The icon used today by scientists and teachers is in fact the outcome of many rearrangements and reinterpretations by the scientific community during that period. This success is often explained as a result of the underlying atomic structure, discovered in the first decades of the 20th century, an explanation that completely neglects the fine structure of the process of ongoing renegotiation and successive stabilizations. How did indeed contemporary scientists navigate in times of reinterpretation? The physicist Lise Meitner and the chemist Ida Noddack were, in different ways, involved in discoveries and interpretations of the periodic system. In 1934, as part of the celebration of the centenary of Dmitri Mendeleev's birth, they each published an article on the system: Meitner in Die Naturwissenschaften, and Noddack in Angewandte Chemie. These two articles, written from the perspectives of a nuclear physicist and a chemist experienced in searching for undiscovered elements, respectively, constitute excellent sources for understanding what new discoveries and insights meant for the meaning and value of the periodic system at the very beginning of the nuclear age in science. Through an analysis of the two contributions, we will argue that resilience is the foremost value of the periodic system. We will also discuss what this value means for the future of the periodic system and its representations.

The periodic system is an icon of science, with an exceptional level of usage around the world. It is especially celebrated as a source of information and pedagogical tool. Although many publications on the history and philosophy of the system have appeared over the years, few of them deal with its underlying values aside from predictability. In this issue, scholars from different disciplines use the history of the periodic system to discuss what the system signifies and has signified for scientists and teachers, as well as for philosophers and historians. By presenting different layers of underlying values as they appear in the eyes of the users, we aim to provide a richer understanding of the periodic system, past and present.

To chemists and chemical educators, there were two important events in the ‘60s and ‘70s. First, in 1961, the agreement between physicists and chemists on the choice of carbon 12 as unique element of reference in the atomic weights table and then in 1971, the definition of mole as the seventh unit of the international system [1]. In both of these issues the Union played its role as expert to the fullest, and established solid grounds for a common language of chemistry across the world. This role is also extended to other matters at a time marked by social changes. Technological progress improved quality of life like never before and the space conquest that opened new horizons, both scientific and technological, to explore. All the while, despite the Cold War, international and interdisciplinary projects are established, and new international organizations, such as UNESCO, appear to cope with the new challenges. Alongside these organizations, the longstanding ICSU and the Union adapt themselves.

The League of Nations’ failure to ensure global peace by solving conflicts through diplomatic and peaceful means prompted Franklin Roosevelt and Winston Churchill to discuss the creation of a more efficient international organization as soon as the Second World War erupted. These preliminary efforts led to the signing of the Charter of the United Nations (UN) in San Francisco in 1945. In January 1946, the first general UN assembly took place, along with the Security Council and the Economic and Social Council. The latter created several international bodies, among them UNESCO. At first, UNESCO seemed to be the continuation of the International Institute for the Intellectual Cooperation (IIIC) coupled with the International Commission for the Intellectual Cooperation (ICIC), but was actually based on new rules [1].