(ORDO NEWS) — Periodic system of chemical elements D.I. Mendeleev developed over many decades – new research was carried out, voids were filled, new elements were discovered.
But the question is – has it ever happened that scientists first added a new element to the table, and then removed it from there? It turns out that this was the case. Didymium is the most famous element that was excluded from D.I. Mendeleev
In 1839 (according to some sources, in 1841), the Swedish chemist and physician Carl Mosander announced the discovery of a new chemical element, didyma (or didymium). The name was derived from the Greek word didymos, which translates as “twin” – the fact is that, in terms of its properties, didymium was very similar to lanthanum.
Why didymium was excluded from the periodic table of chemical elements
In 1879, doubts arose that didymium deserved a place in the periodic table of chemical elements. The thing is that chemical analysis showed that didymium contains particles of samarium, as well as pieces of another unknown element.
And in 1885, the Austrian chemist Carl von Welsbach demonstrated to the public the results of his work – he discovered that didymium was in fact not a separate chemical element, but a mixture of two rare earth elements – neodymium and praseodymium.
Now didymium is used to make special types of glass, as well as to create filters that increase the saturation and contrast of red color when photographing.
What other elements were excluded from the periodic table
Another chemical element excluded from the periodic table was mazur (element 43), which was discovered by a group of German chemists.
Scientists convinced everyone that they had discovered the element in Colombian (now known as niobium) ore in 1925. However, the claim was controversial, as there was no way their peers could replicate their success.
In 1936, American physicist Emilio Segre and Italian chemist Carlo Perrier isolated element 43 from molybdenum foil using a cyclotron – they named it technetium.
However, even the longest-lived isotopes of technetium have short geological half-lives (millions of years), and have only been found in the natural environment in minute trace amounts as a fission product of uranium.
For this reason, the original claim of the discovery of the Mazury is almost universally considered to be erroneous.
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