As of March 2019 the periodic table of the elements is 150 years old. Dimitri Mendeleev, the Russian chemist, presented his version of the table in March of 1869 to a meeting of the Russian Chemical Society. His presentation The Dependence between the Properties of the Atomic Weights of the Elements showed that when the elements are sorted by their atomic weights the chemical properties of individual elements repeat creating groups of elements with similar chemical properties.
Mendeleev's table showed that the chemical elements were not just a collection of facts, but that each element was also part of a pattern that provided clues about the nature of matter itself.
Mendeleev's presentation was the result of not only his work but also the work of many others. What all of this work had in common was based on the central principle of science that "the test of all knowledge is experiment. Experiment is the sole judge of scientific 'truth.'" Experiments, however, can only provide hints about what lies behind experimental findings. The hints demand that the investigator use "imagination to create from these hints the great generalizations--to guess at the wonderful, simple, but very strange patterns beneath them all, and then to experiment to check again whether we have made the right guess." (Feynman, 1964)
The experimental and imaginative work of Antoine Lavoisier and his wife Marie-Anne provides a starting place on the way to Mendeleev. Marie-Anne had worked very hard learning how to make careful measurements to record the results of chemical reactions. The success of her work resulted in the Lavoisiers' observation that the quantities of substances that go into a reaction will equal the quantities of the reactions products.
The Lavoisiers' careful quantitative methods led to the discovery of oxygen (1778) and hydrogen (1783), as well as leading them to a definition of an element as a single substance that cannot be further reduced and is therefore the basis for all other chemical compounds.
The Lavoisiers' experimental demonstration of the conservation of matter hints that there is a something elemental, a particle, for example, that endures as chemicals are transformed into substances with new properties.
It was the Englishman John Dalton, in the first decade of the nineteenth century, who imagined that the invisible mechanism that underlay these hints were “small particles [that he] called atoms.” He reasoned further that since different chemicals had different properties, each of their atoms must have different sizes since he also found that different elements had different weights. He postulated that the atoms of a given element maintained constant in size and mass. Because of this, when different elements combine, they do so in simple whole-number ratios to form chemical compounds in which atoms are combined and rearranged.
Dalton’s imagined atoms represent a useful way to think about experimental findings; they are an imagined reality—the existence of “real” atoms would not be demonstrated for another century.
The power of this useful fiction is shown by the rapid rate of discovery of elements following Dalton: sodium and potassium (1807); magnesium, calcium, strontium, barium, and boron (1808); iodine (1811); cadmium, selenium (1817); Lithium (1821); Silicon (1823); Aluminum and bromine (1825); thorium, lanthanum (1838); erbium (1843); ruthenium (1844); cesium (1860); rubidium (1860); thallium (1861); indium (1863); helium (1868).
While investigators had realized that some elements seemed to be related because they shared some properties in common and several of investigators attempted to explain why, none were successful until Mendeleev’s 1869 table.
Mendeleev’s table transformed a collection of data into knowledge using the hints provided by experimental data from Lavoisier, Dalton and others to tease out “the wonderful, simple, but very strange patterns” revealed by them.
On a single page the modern periodic table of the elements a chemist has access to a huge amount of information in addition to the atomic weights: elements with similar chemical properties in the 18 groups of elements, the trend from metal on the left to non-metals on the right; electron configuration and how the electron shells are filled.
The anonymous author of a March 2019 article The Economist describes the table as “one of science’s greatest creations…How it was created is a perfect illustration of process of scientific progress.”
Feynman, Richard (1964). Feynman: The Feynman Lectures on Physics
Royal Society of Chemistry Development of the periodic table
The Economist. The heart of the matter, March 2nd-8th, 2019, pp. 64-67.
A gallery of modern versions of the periodic table of elements can be viewed here.
Mendeleev’s 1869 table of elements (p. 1) is found on Mendeleev’s Wikipedia page; Lavoisier’s Traité de Chimi image (p.2 ) can be found on the Traite de Chimi Wikipedia page; and John Dalton’s list of chemical elements (1805) can be found on the John Dalton Wikipedia page.
Dr. John HOlton
Dr. John Holton joined the S²TEM Centers SC in July of 2013, as a research associate with an emphasis on the STEM literature including state and local STEM plans from around the nation.