Dmitri Mendeleev published a
periodic table of the
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
s in 1869 based on properties that appeared with some regularity as he laid out the elements from lightest to heaviest. 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, Mendeleev used the prefixes ''
eka''- , ''
dvi''- or ''
dwi-'', and ''
tri''-, from the
Sanskrit
Sanskrit (; attributively , ; nominally , , ) is a classical language belonging to the Indo-Aryan branch of the Indo-European languages. It arose in South Asia after its predecessor languages had diffused there from the northwest in the late ...
names of digits 1, 2, and 3, depending upon whether the predicted element was one, two, or three places down from the known element of the same
group
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
in his table. For example,
germanium was called eka-silicon until its discovery in 1886, and
rhenium
Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one ...
was called dvi-
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
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 element
The transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of these elements are unstable and decay radioactively into other elements. ...
s, for example, ''eka-
radium'' for
unbinilium
Unbinilium, also known as eka-radium or simply element 120, is the hypothetical chemical element in the periodic table with symbol Ubn and atomic number 120. ''Unbinilium'' and ''Ubn'' are the temporary systematic IUPAC name and symbol, which ar ...
. But current official
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
practice is to use a
systematic element name
A systematic element name is the temporary name assigned to an unknown or recently synthesized chemical element. A systematic symbol is also derived from this name.
In chemistry, a transuranic element receives a permanent name and symbol only a ...
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 element
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides ( yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...
s, ''eka-
boron'' (''Eb'', under boron, B, 5), ''eka-
aluminium'' (''Ea'' or ''El'',
under Al, 13), ''eka-
manganese
Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...
'' (''Em'', under Mn, 25), and ''eka-
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
'' (''Es'', under Si, 14), proved to be good predictors of the properties of
scandium (Sc, 21),
gallium (Ga, 31),
technetium
Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous ...
(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 (
ekaborʺ), (
ekaaljuminij), (
ekamarganecʺ), and (
ekasilicij) respectively, following the
pre-1917 Russian orthography.
Initial versions of the periodic table did not distinguish
rare earth elements from
transition element
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that ca ...
s, helping to explain both why Mendeleev's predictions for heavier
unknown element
Unknown or The Unknown may refer to:
Film
* ''The Unknown'' (1915 comedy film), a silent boxing film
* ''The Unknown'' (1915 drama film)
* ''The Unknown'' (1927 film), a silent horror film starring Lon Chaney
* ''The Unknown'' (1936 film), a ...
s did not fare as well as those for the lighter ones and why they are not as well known or documented.
Scandium oxide
Scandium(III) oxide or scandia is a inorganic compound with formula Sc2 O3. It is one of several oxides of rare earth elements with a high melting point. It is used in the preparation of other scandium compounds as well as in high-temperature sys ...
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
eka-boron in 1871, while scandium has an atomic mass of 44.955908.
In 1871, Mendeleev predicted
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, which was discovered, soon after Mendeleev predicted its existence, in 1875 by
Paul Emile Lecoq de Boisbaudran.
Technetium
Technetium is a chemical element with the symbol Tc and atomic number 43. It is the lightest element whose isotopes are all radioactive. All available technetium is produced as a synthetic element. Naturally occurring technetium is a spontaneous ...
was isolated by
Carlo Perrier and
Emilio Segrè
Emilio Gino Segrè (1 February 1905 – 22 April 1989) was an Italian-American physicist and Nobel laureate, who discovered the elements technetium and astatine, and the antiproton, a subatomic antiparticle, for which he was awarded the Nobe ...
in 1937, well after Mendeleev's lifetime, from samples of
molybdenum that had been bombarded with
deuterium nuclei in a
cyclotron
A cyclotron is a type of particle accelerator invented by Ernest O. Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Jan ...
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.
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.
Other predictions
The existence of an element between
thorium (90) and
uranium (92) was predicted by Mendeleev in 1871. In 1900,
William Crookes
Sir William Crookes (; 17 June 1832 – 4 April 1919) was a British chemist and physicist who attended the Royal College of Chemistry, now part of Imperial College London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing t ...
isolated
protactinium
Protactinium (formerly protoactinium) is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds ...
(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, 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
actinide
The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The info ...
s; hence, protactinium does not occupy the place of eka-
tantalum
Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that ...
(under 73) in
group 5 Group 5 may refer to:
*Group 5 element, chemical element classification
*Group 5 (racing)
Group 5 was an FIA motor racing classification which was applied to four distinct categories during the years 1966 to 1982. Initially Group 5 regulations def ...
. Eka-tantalum is actually the
synthetic superheavy element
Superheavy elements, also known as transactinide elements, transactinides, or super-heavy elements, are the chemical elements with atomic number greater than 103. The superheavy elements are those beyond the actinides in the periodic table; the l ...
dubnium
Dubnium is a synthetic chemical element with the symbol Db and atomic number 105. It is highly radioactive: the most stable known isotope, dubnium-268, has a half-life of about 16 hours. This greatly limits extended research on the element.
...
(105).
Mendeleev's 1869 table had implicitly predicted a heavier analog of
titanium (22) and
zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'' ...
(40), but in 1871 he placed
lanthanum (57) in that spot. The 1923 discovery of
hafnium
Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri M ...
(72) validated Mendeleev's original 1869 prediction.
Some other predictions were unsuccessful because he failed to recognise the presence of the lanthanides in the sixth row.
[
]
Later predictions
In 1902, having accepted the evidence for elements helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
and argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice as ...
, Mendeleev placed these noble gases in Group 0 in his arrangement of the elements. As Mendeleev was doubtful of atomic theory to explain the law of definite proportions
In chemistry, the law of definite proportions, sometimes called Proust's law, or law of constant composition states that a given
chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source an ...
, he had no '' a priori'' reason to believe hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
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 (see Neutronium
Neutronium (sometimes shortened to neutrium, also referred to as neutrite) is a hypothetical substance composed purely of neutrons. The word was coined by scientist Andreas von Antropoff in 1926 (before the 1932 discovery of the neutron) for the ...
), and it matches Mendeleev's predictions fairly well.
The heavier of the hypothetical proto-helium elements Mendeleev identified with coronium
Coronium, also called newtonium, was the name of a suggested chemical element, hypothesised in the 19th century. The name, inspired by the solar corona, was given by Gruenwald in 1887. A new atomic thin green line in the solar corona was then con ...
, 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.
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.
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.
Notes
References
Further reading
*
{{Navbox periodic table
*