Mendeleev's predicted elements
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Dmitri Mendeleev published a periodic table of the chemical elements in 1869 based on properties that appeared with some regularity as he laid out the elements from lightest to heaviest.[1] When Mendeleev proposed his periodic table, he noted gaps in the table and predicted that then-unknown elements existed with properties appropriate to fill those gaps. He named them eka-boron, eka-aluminium, eka-silicon, and eka-manganese, with respective atomic masses of 44, 68, 72, and 100.
Prefixes
To give provisional names to his predicted elements,
The eka- prefix was used by other theorists, and not only in Mendeleev's own predictions. Before the discovery,
Original predictions
The four predicted elements lighter than the rare-earth elements, eka-boron (Eb, under boron, B, 5), eka-aluminium (Ea or El,[2] under Al, 13), eka-manganese (Em, under Mn, 25), and eka-silicon (Es, under Si, 14), proved to be good predictors of the properties of scandium (Sc, 21), gallium (Ga, 31), technetium (Tc, 43), and germanium (Ge, 32) respectively, each of which fill the spot in the periodic table assigned by Mendeleev.
The names were written by Dmitri Mendeleev as экаборъ (ekaborʺ), экаалюминій (ekaaljuminij), экамарганецъ (ekamarganecʺ), and экасилицій (ekasilicij) respectively, following the pre-1917 Russian orthography.
Initial versions of the periodic table did not distinguish
In 1871, Mendeleev predicted
Property | Eka-aluminium | Gallium | |
---|---|---|---|
Atomic Mass | 68 | 69.723 | |
Density (g/cm3) | 6.0 | 5.91 | |
Melting point (°C) | Low | 29.76 | |
Oxide | Formula | Ea2O3 | Ga2O3 |
Density | 5.5 g/cm3 | 5.88 g/cm3 | |
Solubility | Soluble in both alkalis and acids | ||
Chloride | Formula | Ea2Cl6 | Ga2Cl6 |
Volatility | Volatile | Volatile |
Technetium was isolated by Carlo Perrier and Emilio Segrè in 1937, well after Mendeleev's lifetime, from samples of molybdenum that had been bombarded with deuterium nuclei in a cyclotron by Ernest Lawrence. Mendeleev had predicted an atomic mass of 100 for eka-manganese in 1871, and the most stable isotope of technetium is 98Tc.[4]
Germanium was isolated in 1886 and provided the best confirmation of the theory up to that time, due to its contrasting more clearly with its neighboring elements than the two previously confirmed predictions of Mendeleev do with theirs.
Property | Eka-silicon | Germanium | |
---|---|---|---|
Atomic Mass | 72 | 72.630 | |
Density (g/cm3) | 5.5 | 5.323 | |
Melting point (°C) | High | 938 | |
Color | Grey | Grey | |
Oxide | Type | Refractory dioxide | |
Density (g/cm3) | 4.7 | 4.228 | |
Activity | Feebly basic | Feebly basic | |
Chloride | Boiling point | Under 100 °C | 86.5 °C (GeCl4) |
Density (g/cm3) | 1.9 | 1.879 |
Other predictions
The existence of an element between thorium (90) and uranium (92) was predicted by Mendeleev in 1871. In 1900, William Crookes isolated protactinium (91) as a radioactive material deriving from uranium that he could not identify. Different isotopes of protactinium were identified in Germany in 1913 and in 1918,[5] but the name protactinium was not given until 1948. Since the acceptance of Glenn T. Seaborg's actinide concept in 1945, thorium, uranium and protactinium have been classified as actinides; hence, protactinium does not occupy the place of eka-tantalum (under 73) in group 5. Eka-tantalum is actually the 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.
Mendeleev[6] | Modern names | Atomic Number |
---|---|---|
eka-boron | scandium, Sc | 21 |
eka-aluminium | gallium, Ga | 31 |
eka-silicon | germanium, Ge | 32 |
eka-manganese | technetium, Tc | 43 |
dvi-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.[6]
Later predictions
In 1902, having accepted the evidence for elements
The heavier of the hypothetical proto-helium elements Mendeleev identified with
The lightest of the Group 0 gases, the first in the periodic table, was assigned a theoretical atomic mass between 5.3×10−11
Mendeleev later published a theoretical expression of
Notes
- ^ Citing from the 1871 article:[2]: 45
Элементъ этотъ предлагаю предварительно назвать 'экаборомъ', производя это названіе отъ того что онъ слѣдуетъ за боромъ, какъ первый элементъ четныхъ группъ, а слогъ 'эка' производится отъ санскритскаго слова, обозначающаго 'одинъ'. Eb=45. Экаборъ ...
I propose that this element be called ekaboron first, producing this name from the fact that it comes after the boron, like the first element of even groups, and the syllable eka is derived from a Sanskrit word that stands for one. Eb=45. Ekaboron ...
References
- ^ Kaji, Masanori (2002). "D. I. Mendeleev's concept of chemical elements and The Principles of Chemistry" (PDF). Bulletin for the History of Chemistry. 27 (1): 4–16. Archived from the original (PDF) on 2008-12-17. Retrieved 2006-11-09.
- ^ a b c Mendeleev, D. (1871). "The natural system of elements and its application to the indication of the properties of undiscovered elements". Journal of the Russian Chemical Society (in Russian). 3: 25–56. Retrieved 23 August 2017.
- Bibcode:2004physics..11080K.
- atomic mass number of 98 which is distinct from an atomic mass in that it is a count of nucleons in the nucleus of one isotope and is not an actual mass of an average sample (with a natural collection of isotopes) relative to 12C. The 98Tc isotope has a mass of 97.907214. For elements that are not stable enough to persist from the creation of the Earth, the convention is to report the atomic mass number of the most stable isotope in place of the naturally occurring atomic-mass average. "Technetium". Archived from the originalon 2006-12-03. Retrieved 2006-11-11..
- ISBN 0-19-850340-7.
- ^ S2CID 104132201.
- ^ Mendeleev, D. (1902-03-19). Osnovy Khimii [The Principles of Chemistry] (in Russian) (7th ed.).
- hdl:2268/71737.
- ^ "Identification of Spectral Lines – History of Coronium". laserstars.org.
- ^ Mendeleev, D. (1903). Popytka khimicheskogo ponimaniia mirovogo efira (in Russian). St. Petersburg.
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An English translation appeared as
Mendeléeff, D. (1904). An Attempt Towards A Chemical Conception Of The Ether. Translated by Kamensky, G. Longmans, Green & Co. - S2CID 96809512.
Further reading
- Scerri, Eric (2007). The Periodic Table: Its Story and Its Significance. New York: Oxford University Press. ISBN 978-0-19-530573-9.