Science HolicThe History of the Periodic Table
Author: William Tsay
Editors: Jasleen Matharu and He-Hanson Xuan
Artist: Jennifer Hu
The Periodic Table of Elements is ubiquitous in science classrooms and has become an icon of chemistry. It contains 118 known elements and their chemical symbols, atomic numbers, and atomic masses but is continuously advancing as scientists discover new elements. However, the arrangement of the periodic table was determined more than a century ago, before the discovery of all current known elements. How did scientists invent this complex table before they discovered all present-day elements, and can we see any patterns?
In 1860, the International Conference on Chemistry of Germany published a list of elements and their atomic masses. British chemist John Newlands decided to arrange these elements by ascending atomic mass but left no spaces for undiscovered elements. Five years later, Dimitri Mendeleev produced a similar table; however, in contrast, he left some spots open for the unknown elements, similar to a puzzle piece. The discovery of some unknown elements like gallium and germanium soon confirmed his version of the periodic table, winning it universal recognition and allowing Mendeleev to be credited for the discovery of the periodic table.
However, Mendeleev’s table isn’t the modern periodic table. In 1913, British scientist Henry Moseley modified Mendeleev’s table; he arranged it not by atomic mass but by atomic number, claiming that similar properties recur periodically. When World War 1 broke out in Europe, Moseley enlisted in the army and was unfortunately killed in combat. His discovery was groundbreaking, but he was never awarded for it.
The modern periodic table of elements is ordered by atomic mass and has many patterns, known as periodic trends. The table consists of 18 groups (columns) and seven periods (rows). All elements in the same group share similar chemical properties. Characteristics like electronegativity, ionization energy, atomic radius, and metallic character all follow trends on the periodic table. Is it a coincidence that so many patterns are visible on the table? Maybe not, but the fact that scientists were able to arrange the periodic table of elements without complete knowledge of their existences elicits amazement.
Citations
Moseley's Periodic Table, https://corrosion-doctors.org/Periodic/Periodic-Moseley.htm.
Guharay, Deboleena M. “A Brief History of the Periodic Table.” American Society for
Biochemistry and Molecular Biology, 7 Feb. 2021, https://www.asbmb.org/asbmb-
today/science/020721/a-brief-history-of-the-periodic-table.