Editing Mendeleev's predicted elements (section)

== Other predictions ==

The existence of an element between [[thorium]] (90) and [[uranium]] (92) was predicted by Mendeleev in 1871. In 1900, [[William Crookes]] isolated a radioactive material deriving from uranium that he could not identify, which was later proven to be mixture of <sup>234</sup>Th and <sup>234m</sup>Pa. Protactinium-234m (named "brevium") was identified in Germany in 1913,<ref>{{cite book | last = Emsley | first = John | title = Nature's Building Blocks | edition = Hardcover, First | publisher = [[Oxford University Press]] | year = 2001 | pages = [https://archive.org/details/naturesbuildingb0000emsl/page/347 347] | isbn = 0-19-850340-7 | url = https://archive.org/details/naturesbuildingb0000emsl/page/347 }}</ref> but the name ''[[protactinium]]'' was not given until 1918, when protactinium-231 was discovered. Since the acceptance of [[Glenn T. Seaborg]]'s [[actinide concept]] in 1945, thorium, uranium and protactinium have been classified as [[actinide]]s; hence, protactinium does not occupy the place of eka-[[tantalum]] (under 73) in [[Group 5 element|group 5]]. Eka-tantalum is actually the [[synthetic element|synthetic]] [[superheavy element]] [[dubnium]] (105).

Mendeleev's 1869 table had implicitly predicted a heavier analog of [[titanium]] (22) and [[zirconium]] (40), but in 1871 he placed [[lanthanum]] (57) in that spot. The 1923 discovery of [[hafnium]] (72) validated Mendeleev's original 1869 prediction.

{| class="wikitable"
! Mendeleev<ref name=stewart>{{cite journal | title=Mendeleev's predictions: success and failure | author=Philip J. Stewart | journal=Foundations of Chemistry | volume= 21 | pages=3–9 | date=2019| doi=10.1007/s10698-018-9312-0 | s2cid=104132201 | doi-access=free }}</ref>
! Modern names
! Atomic Number
|-
| eka-boron
| scandium, Sc
| 21
|-
| eka-aluminium
| gallium, Ga
| 31
|-
| eka-silicon
| germanium, Ge
| 32
|-
| eka-manganese
| technetium, Tc
| 43
|-
| tri-manganese
| rhenium, Re
| 75
|-
| dvi-tellurium
| polonium, Po
| 84
|-
| dvi-caesium
| francium, Fr
| 87
|-
| eka-tantalum
| protactinium, Pa
| 91
|}

Some other predictions were unsuccessful because he failed to recognise the presence of the lanthanides in the sixth row.<ref name=stewart/>

In 1902, [[Bohuslav Brauner]] placed lanthanides in a special series instead of Mendeleev's extra period, so he renamed Mendeleev's tri-manganese as dvi-manganese and dvi-tellurium as eka-tellurium (polonium had already been discovered, but its chemical properties had not yet been studied). Dvi-caesium was renamed eka-caesium.<ref>{{cite journal|last=Brauner|first=Bohuslav|journal=Zhurnal obshcheĭ khimii|year=1902|lang=ru|volume=34|pages=142–153|title=О положеніи рѣдкоземельныхъ элементовъ въ періодической системѣ Менделѣева|url=https://archive.org/details/zhurnalobshcheik3419russ/page/n193/mode/2up}}</ref>