Standardizing the Periodic Table: Science, Pedagogy, and Graphical Representation

The standard periodic table of the elements is an icon of chemistry and a symbol of science as a whole.  It is a tool and guide not only for research but for teaching, as well.  Given these roles, it is important to understand the many aspects of its history.  How did the periodic law originate?  Why was it accepted?  Why are there so many graphical representations?  Who developed the standard form of the periodic table?  The answers to the questions are bound up in the sciences of chemistry and physics, but also in pedagogy.

When we think of the periodic table, many of us have a specific image in mind, that of the table of the elements which was in our chemistry textbook and hanging on the wall of our classroom.  Since the periodic law was first outlined in the 1860s, there have been approximately a thousand periodic tables created by scientists and science educators.  Prior to World War II, textbooks often included more than one table and these tables varied from text to text.  Periodic table wall charts became commercially available in the 1920s, however before then teachers would make their own periodic table charts, often based on their own graphical representation.  Forms resembling the periodic table we are most familiar with began to appear in the early 20^th century but it wasn't until the 1950s that textbooks began to use a standardized table.

The different graphic representations reveal tensions within chemistry and between chemistry and physics.  Through the end of the 19^th century, there was much debate over where certain groups of elements belonged in the periodic system.  Discoveries in the early 20^th century changed the underpinnings of the periodic law; no longer was atomic weight, a chemical characteristic of elements, the organizing principle but rather atomic number, a physical characteristic of atoms.  Debates shifted from where elements belonged chemically to how much chemical and physical information it was important to display on the table.

The graphical representation of the periodic law was also in flux.  Dmitri Mendeleev, the Russian chemist who is generally recognized as the discoverer of the periodic law, himself drew more than fifty tables.  In the last decades of the 19^th century and into the early decades of the 20^th century, spiral and helical forms proved more popular than tabular forms.  Three-dimensional tables were also developed.  Tabular forms, however, began to be more common in the 20^th century, until the development of the standard table, which became the dominant form after World War II.

This poster comes out of my dissertation research.  Specific tables from the 19^th and 20^th centuries illustrate the changes which occurred within science as well as pedagogy.  These tables also illustrate different graphical representations of the periodic law which were popular at various times during the last 150 years.