Charles Janet (; 15 June 1849 – 7 February 1932) was a French engineer, company director, inventor and biologist. He is also known for his innovative ''left-step'' presentation of the

periodic table The periodic table, also known as the periodic table of the (chemical) elements, is a rows and columns arrangement of the chemical elements. It is widely used in chemistry, physics, and other sciences, and is generally seen as an icon of ch ...

of chemical elements.

Life and work

Janet graduated from the École des Mines and worked for some years in munitions. He then married the daughter of the owner of a manufacturing company and worked for it for the rest of his life, finding time for research in various branches of science. His collection of 40,000 fossils and other specimens was unfortunately dispersed after his death. His studies of the morphology of the head of ants, wasps and bees, and his micrographs were of remarkable quality. He also worked on plant biology and finally wrote a series of papers on evolution. He was a prolific inventor and designed much of his own equipment, including the formicarium, in which an ant colony is made visible by being formed between two panes of glass. In 1927 he turned his attention to the

and wrote a series of six articles in French, which were privately printed and never widely circulated. His only article in English was poorly edited and gave a confused idea of his thinking.

Chemical ideas

Janet started from the fact that the series of chemical elements is a continuous sequence, which he represented as a helix traced on the surfaces of four nested cylinders. By various geometrical transformations he derived several striking designs, one of which is his "left-step

", in which hydrogen and helium are placed above lithium and beryllium. It was only later that he realized that his arrangement agreed perfectly with quantum theory and the electronic structure of the atom. He placed the actinides under the lanthanides twenty years before Glenn Seaborg, and he continued the series to element 120. Janet's table differs from the standard table in placing the s-block elements on the right, so that the subshells of the periodic table are arranged in the order , , , ''n''s, from left to right. There is then no need to interrupt the sequence or move the f block into a 'footnote'. He believed that no elements heavier than number 120 would be found, so he did not envisage a g block. In terms of atomic quantum numbers, each row corresponds to one value of the sum where ''n'' is the principal quantum number and ℓ the azimuthal quantum number. The table therefore corresponds to the Madelung rule, which states that atomic subshells are filled in the order of increasing values of . The philosopher of chemistry Eric Scerri has written extensively in favor of Janet's left-step periodic table, and it is being increasingly discussed as a candidate for the optimal or most fundamental form of the periodic table. Janet also envisaged an element zero whose 'atom' would consist of two neutrons, and he speculated that this would be the link to a mirror-image table of elements with negative atomic numbers – in effect

anti-matter In modern physics, antimatter is defined as matter composed of the antiparticles (or "partners") of the corresponding particles in "ordinary" matter. Antimatter occurs in natural processes like cosmic ray collisions and some types of radioacti ...

. He also conceived of heavy hydrogen (deuterium). He died just before the discovery of the neutron, the

positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...

and heavy hydrogen. His work was championed most notably by

Edward G. Mazurs Edward G. Mazurs (1894–1983) was a chemist who wrote a history of the periodic system of the chemical elements which is still considered a "classic book on the history of the periodic table". Originally self-published as ''Types of graphic repr ...

Family

Charles Janet is better known than his brother, Armand Janet, also an engineer and entomologist. Armand Janet became renowned as a

lepidopterist Lepidopterology ()) is a branch of entomology concerning the scientific study of moths and the three superfamilies of butterflies. Someone who studies in this field is a lepidopterist or, archaically, an aurelian. Origins Post- Renaissance, t ...

and served as president of the Société entomologique de France in 1911. Armand Janet is also known as a caver and explorer and was one of the first to explore the Verdon Gorge.

References and notes

External links

Biographie synthétique de Charles Janet
*Eric Scerri, 2020
''The Periodic Table: Its Story and Its Significance''
2nd edition, Oxford University Press, New York, {{DEFAULTSORT:Janet, Charles 1932 deaths 1849 births 19th-century French chemists French lepidopterists People involved with the periodic table 19th-century French engineers 20th-century French engineers 20th-century chemists 19th-century French zoologists 20th-century French zoologists 19th-century biologists 20th-century biologists French biologists 19th-century French inventors 20th-century French inventors