Mendeleev's predicted elements

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 as-then-unknown elements existed with properties appropriate to fill those gaps. He named them eka-boron, eka-aluminium and eka-silicon, with respective atomic masses of 44, 68, and 72.


To give provisional names to his predicted elements, Mendeleev used the prefixes eka- /ˈiːkə-/,[note 1] dvi- or dwi-, and tri-, from the Sanskrit names of digits 1, 2, and 3,[3] depending upon whether the predicted element was one, two, or three places down from the known element of the same group in his table. For example, germanium was called eka-silicon until its discovery in 1886, and rhenium was called dvi-manganese before its discovery in 1926.

The eka- prefix was used by other theorists, and not only in Mendeleev's own predictions. Before the discovery, francium was referred to as eka-caesium, and astatine as eka-iodine. Sometimes, eka- is still used to refer to some of the transuranic elements, for example, eka-actinium (or dvi-lanthanum) for unbiunium. But current official IUPAC practice is to use a systematic element name based on the atomic number of the element as the provisional name, instead of being based on its position in the periodic table as these prefixes require.

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, which fill the spot in the periodic table assigned by Mendeleev.

The names were written by Mendeleev as экаборъ (ekabor), экаалюминій (ekaalyuminiy), экамарганецъ (ekamarganets), and экасилицій (ekasilitsiy) respectively, following the pre-1917 Russian orthography.

Initial versions of the periodic table did not distinguish rare earth elements from transition elements, helping to explain both why Mendeleev's predictions for heavier unknown elements did not fare as well as those for the lighter ones and why they are not as well known or documented.

Scandium oxide was isolated in late 1879 by Lars Fredrick Nilson; Per Teodor Cleve recognized the correspondence and notified Mendeleev late in that year. Mendeleev had predicted an atomic mass of 44 for ekaboron in 1871, while scandium has an atomic mass of 44.955908.

In 1871 Mendeleev predicted[2] the existence of a yet-undiscovered element he named eka-aluminium (because of its proximity to aluminium in the periodic table). The table below compares the qualities of the element predicted by Mendeleev with actual characteristics of gallium (discovered in 1875 by Paul Emile Lecoq de Boisbaudran).

Property Eka-aluminium Gallium
atomic mass 68 69.723
density (g/cm3) 6.0 5.91
melting point (°C) low 29.76
oxide's formula Ea2O3 (density: 5.5 g/cm3) (soluble in both alkalis and acids) Ga2O3 (density: 5.88 g/cm3) (soluble in both alkalis and acids)
chloride's formula Ea2Cl6 (volatile) Ga2Cl6 (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 ekamanganese 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 refractory dioxide
oxide density (g/cm3) 4.7 4.228
oxide activity feebly basic feebly basic
chloride boiling point under 100 °C 86.5 °C (GeCl4)
chloride 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 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 93) in what is now called 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.

Later predictions

In 1902, having accepted the evidence for elements helium and argon, Mendeleev placed these noble gases in Group 0 in his arrangement of the elements.[6] As Mendeleev was doubtful of atomic theory to explain the law of definite proportions, he had no 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 neutrons in this place, and it matches Mendeleev's predictions fairly well.

The heavier of the hypothetical proto-helium elements Mendeleev identified with coronium, named by association with an unexplained spectral line in the Sun's corona. A faulty calibration gave a wavelength of 531.68 nm, which was eventually corrected to 530.3 nm, which Grotrian and Edlén identified as originating from Fe XIV in 1939.[7][8]

The lightest of the Group 0 gases, the first in the periodic table, was assigned a theoretical atomic mass between 5.3×10−11 and 9.6×10−7. 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.[9][10]

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.


  1. ^ 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 ...


  1. ^ 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.
  2. ^ 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.
  3. ^ Kak, Subhash (2004). "Mendeleev and the Periodic Table of Elements". Sandhan. 4 (2): 115–123. arXiv:physics/0411080v2. Bibcode:2004physics..11080K.
  4. ^ This is 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. "Archived copy". Archived from the original on 2006-12-03. Retrieved 2006-11-11.CS1 maint: Archived copy as title (link).
  5. ^ Emsley, John (2001). Nature's Building Blocks (Hardcover, First ed.). Oxford University Press. p. 347. ISBN 0-19-850340-7.
  6. ^ Mendeleev, D. (1902-03-19). Osnovy Khimii [The Principles of Chemistry] (in Russian) (7th ed.).
  7. ^ Swings, P. (July 1943). "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" (PDF). Astrophysical Journal. 98 (119): 116–124. Bibcode:1943ApJ....98..116S. doi:10.1086/144550.
  8. ^ "Identification of Spectral Lines – History of Coronium".
  9. ^ Mendeleev, D. (1903). Popytka khimicheskogo ponimaniia mirovogo efira (in Russian). St. Petersburg.
    An English translation appeared as
    Mendeléeff, D. (1904). G. Kamensky (translator) (ed.). An Attempt Towards A Chemical Conception Of The Ether. Longmans, Green & Co.
  10. ^ Bensaude-Vincent, Bernadette (1982). "L'éther, élément chimique: un essai malheureux de Mendéleev en 1904". British Journal for the History of Science. 15 (2): 183–188. doi:10.1017/S0007087400019166. JSTOR 4025966.

Further reading

  • Scerri, Eric (2007). The Periodic Table: Its Story and Its Significance. New York: Oxford University Press. ISBN 0-19-530573-6.
1875 in science

The year 1875 in science and technology involved some significant events, listed below.

Actinide concept

In nuclear chemistry, the actinide concept proposed that the actinides form a second inner transition series homologous to the lanthanides. Its origins stem from observation of lanthanide-like properties in transuranic elements in contrast to the distinct complex chemistry of previously known actinides. Glenn T. Seaborg, one of the researchers who synthesized transuranic elements, proposed the actinide concept in 1944 as an explanation for observed deviations and a hypothesis to guide future experiments. It was accepted shortly thereafter, resulting in the placement of a new actinide series comprising elements 89 (actinium) to 103 (lawrencium) below the lanthanides in Dmitri Mendeleev's periodic table of the elements.

Dmitri Mendeleev

Dmitri Ivanovich Mendeleev (English: MEN-dəl-AY-əf; Russian: Дмитрий Иванович Менделеев, tr. Dmítriy Ivánovich Mendeléyev, IPA: [ˈdmʲitrʲɪj ɪˈvanəvʲɪtɕ mʲɪndʲɪˈlʲejɪf] (listen); 8 February 1834 – 2 February 1907 [OS 27 January 1834 – 20 January 1907]) was a Russian chemist and inventor. He formulated the Periodic Law, created a farsighted version of the periodic table of elements, and used it to correct the properties of some already discovered elements and also to predict the properties of eight elements yet to be discovered.

Index of physics articles (M)

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Indomania or Indophilia refer to the special interest India, Indians and Indian cultures have generated in the Western world, more specifically the culture and civilisation of the Indian subcontinent, especially in Germany. The initial British interest in governing their newly conquered territories awoke the interest in India, especially its culture and ancient history. Later the people with interests in Indian aspects came to be known as Indologists and their subject as Indology. Its opposite is Indophobia.

List of chemical element name etymologies

This article lists the etymology of chemical elements of the periodic table.

Numeral prefix

Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and other European languages, they are used to coin numerous series of words, such as unicycle – bicycle – tricycle, dyad – triad – decade, biped – quadruped, September – October – November – December, decimal – hexadecimal, sexagenarian – octogenarian, centipede – millipede, etc. There are two principal systems, taken from Latin and Greek, each with several subsystems; in addition, Sanskrit occupies a marginal position.

There is also an international set of metric prefixes, which are used in the metric system, and which for the most part are either distorted from the forms below or not based on actual number words.

Sanskrit studies

Sanskrit has been studied by Western scholars since the late 18th century.

In the 19th century, the study of Sanskrit played a crucial role in the development of the field of comparative linguistics of the Indo-European languages. During the British Raj (1857-1947), Western scholars edited many Sanskrit texts which had survived in manuscript form.

The study of Sanskrit grammar and philology remains important both in the field of Indology and of Indo-European studies.

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