Editing Mendeleev's predicted elements (section)

== Later predictions ==

In 1902, having accepted the evidence for elements [[helium]] and [[argon]], Mendeleev placed these noble gases in [[noble gas|Group 0]] in his arrangement of the elements.<ref>{{cite book|last=Mendeleev|first=D.|author-link=Dmitri Mendeleev|title= Osnovy Khimii [The Principles of Chemistry]|edition=7th| date=1902-03-19|language=ru}}</ref> As Mendeleev was doubtful of [[atomic theory]] to explain the [[law of definite proportions]], he had no ''[[A priori and a posteriori (philosophy)|a priori]]'' reason to believe [[hydrogen]] was the lightest of elements, and suggested that a hypothetical lighter member of these chemically inert Group 0 elements could have gone undetected and be responsible for [[radioactivity]]. Currently some periodic tables of elements put lone [[neutron]]s in this place (see [[neutronium]]) but no such element has ever been detected.

The heavier of the hypothetical proto-helium elements Mendeleev identified with [[coronium]], named by association with an unexplained spectral line in the [[solar corona|Sun's corona]]. A faulty calibration gave a wavelength of 531.68&nbsp;nm, which was eventually corrected to 530.3&nbsp;nm, which [[Walter Grotrian|Grotrian]] and [[Bengt Edlén|Edlén]] identified as originating from [[iron|Fe]] XIV (i.e. Fe<sup>13+</sup>) in 1939.<ref>{{cite journal|last=Swings|first=P.|journal=Astrophysical Journal|title=Edlén's Identification of the Coronal Lines with Forbidden Lines of Fe X, XI, XIII, XIV, XV; Ni XII, XIII, XV, XVI; Ca XII, XIII, XV; A X, XIV|date=July 1943|volume=98|issue=119|pages=116–124|doi=10.1086/144550|bibcode=1943ApJ....98..116S|hdl=2268/71737 |url=http://orbi.ulg.ac.be/bitstream/2268/71737/1/SWINGS_1943_edlen-s-identification-of-the-coro.pdf}}</ref><ref>{{cite web|url=http://laserstars.org/spectra/Coronium.html|title=Identification of Spectral Lines – History of Coronium|website=laserstars.org}}</ref>

The lightest of the Group 0 gases, the first in the periodic table, was assigned a theoretical atomic mass between {{val|5.3|e=-11|ul=u}} and {{val|9.6|e=-7|u=u}}. The kinetic velocity of this gas was calculated by Mendeleev to be 2,500,000 meters per second. Nearly massless, these gases were assumed by Mendeleev to permeate all matter, rarely interacting chemically. The high mobility and very small mass of the trans-hydrogen gases would result in the situation that they could be rarefied, yet appear to be very dense.<ref>{{cite book |last=Mendeleev|first=D.|author-link=Dmitri Mendeleev|title=Popytka khimicheskogo ponimaniia mirovogo efira|year=1903|language=ru|location=St. Petersburg}}<br />An English translation appeared as<br />{{cite book|last=Mendeléeff|first=D.|author-link=Dmitri Mendeleev|translator-first1=G. |translator-last1=Kamensky|title=An Attempt Towards A Chemical Conception Of The Ether|publisher=Longmans, Green & Co.|year=1904}}</ref><ref>{{cite journal|last=Bensaude-Vincent|first=Bernadette|title=L'éther, élément chimique: un essai malheureux de Mendéleev en 1904|journal=British Journal for the History of Science|year=1982|volume=15|issue=2|pages=183–188|doi=10.1017/S0007087400019166 | jstor=4025966|s2cid=96809512 }}</ref>

Mendeleev later published a theoretical expression of [[the ether]] in a small booklet entitled ''A Chemical Conception of the Ether'' (1904). His 1904 publication again contained two atomic elements smaller and lighter than hydrogen. He treated the "ether gas" as an interstellar atmosphere composed of at least two elements lighter than hydrogen. He stated that these gases originated due to violent bombardments internal to stars, the Sun being the most prolific source of such gases. According to Mendeleev's booklet, the interstellar atmosphere was probably composed of several additional elemental species.<!-- is this 1904 reference distinct from the 1903/1904 publication? -->