|Pronunciation|| / /(|
|Hassium in the periodic table|
|Atomic number (Z)||108|
|Element category||Transition metal|
|Electron configuration||[ Rn ] 5f14 6d6 7s2|
|Electrons per shell||2, 8, 18, 32, 32, 14, 2|
|Phase at STP||solid (predicted)|
|Density (near r.t.)||41 g/cm3(predicted)|
|Oxidation states||(+2), (+3), (+4), (+6), +8 (brackets: prediction)|
|Atomic radius||empirical:126 pm (estimated)|
|Covalent radius||134 pm(estimated)|
|Crystal structure|| hexagonal close-packed (hcp)|
|Naming||after Hassia, Latin for Hesse, Germany, where it was discovered|
|Discovery||Gesellschaft für Schwerionenforschung (1984)|
|Main isotopes of hassium|
Hassium is a chemical element with the symbol Hs and the atomic number 108. It is not known to occur in nature and has been made only in laboratories in minuscule quantities. Hassium is highly radioactive; the most stable known isotope, 269Hs, has a half-life of approximately 16 seconds.
The first attempts to synthesize element 108 were made in two different experiments at the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, in 1978. More attempts were made at the same venue in 1983 and then in 1984; the latter resulted in a claim that element 108 had been produced. Later in 1984, an attempt was made at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Hesse, West Germany, which claimed to have synthesized it. The 1993 report by the Transfermium Working Group, formed by the International Union of Pure and Applied Chemistry and the International Union of Pure and Applied Physics, concluded the report from Darmstadt was more conclusive on its own and the major credit was assigned to the German scientists, who then chose the name hassium after the German state of Hesse.
In the periodic table of the elements, hassium is a transactinide element, a member of the 7th period and group 8; it is thus the sixth member of the 6d series of transition metals. Chemistry experiments have confirmed that hassium behaves as the heavier homologue to osmium, in group 8, reacting readily with oxygen to form a volatile tetroxide. The chemical properties of hassium have only been partly characterized but they compare well with the chemistry of the other group 8 elements.
A superheavyatomic nucleus is created in a nuclear reaction that combines two other nuclei of unequal size into one; roughly, the more unequal the two nuclei in terms of mass, the greater the possibility that the two react. The material made of the heavier nuclei is made into a target; the target is then bombarded by the beam of lighter nuclei. Two nuclei could only fuse into one if they approach each other closely enough; normally, nuclei (all positively charged) repel each other due to electrostatic repulsion. The strong force can overcome this repulsion but only within a very short distance from a nucleus; beam nuclei are thus greatly accelerated in order to make such repulsion insignificant compared to the velocity of the beam nucleus. Each pair of a target and a beam is characterized by its cross section—the probability that fusion will occur if two nuclei approach one another expressed in terms of the transverse area that the incident particle must hit in order for the fusion to occur. This fusion may occur as a result of the quantum effect in which nuclei can tunnel through electrostatic repulsion.
The resulting merger is invariably an excited state—termed a compound nucleus—and thus it is very unstable and cannot exist for a length of time that would ensure that the nucleons (protons and neutrons) arrange themselves into a new nucleus. The definition by the IUPAC/IUPAP Joint Working Party states that a chemical element can only be recognized as such if a nucleus of it has not decayed within 10−14 seconds. This value was chosen as an estimate of how long it takes a nucleus to acquire its outer electrons and thus display its chemical properties.To reach a more stable state, the temporary merger may eject a few neutrons, which allows the nucleons to form a nucleus.
Produced nuclei are recognized by the type of decay they undergo. Alpha and beta decays are registrable by the emitted alpha or beta particles (with the exception of electron capture, which emits no such particle) and they produce nuclei that are clear to determine before the actual decay; if such a decay or a series of consecutive decays produces a known nucleus, the original product of a reaction can be easily determined. The known nucleus could be recognized by the specific characteristics of decay it undergoes, such as decay energy (or more specifically, the kinetic energy of the emitted particle). Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot easily be determined. It is thus sought that the known nucleus to which the newly synthesized nucleus decay into itself undergoes alpha or beta decays, rather than spontaneous fission. The product of a reaction can also be determined by what chemistry it (or its daughter from consecutive alpha and beta decays) displays, but chemical identification can only identify an element, rather than an exact isotope.
The chemical element with the highest atomic number—number of protons in an atomic nucleus; such a number constitutes an exhaustive definition of an element—that exists in nature in significant quantities in uranium, element 92; all elements with higher atomic numbers were discovered by synthesis rather than by observation in nature. The first such element, element 93, later named neptunium, was discovered in 1940 at the University of California in Berkeley, California, United States. Elements through 101 were discovered at this university's Radiation Laboratory (now named Lawrence Berkeley National Laboratory). Starting with element 102, another major facility emerged that claimed discoveries of new elements: the Joint Institute for Nuclear Research (JINR) in Dubna, Moscow Oblast, Russian SFSR, Soviet Union, which first reported synthesis of a new element in 1958. Another major venue—Gesellschaft für Schwerionenforschung (GSI; Institute for Heavy Ion Research) in Darmstadt, Hesse, West Germany—first reported synthesis of a new element (element 107) in 1981. These facilities often claimed discoveries of a new element. Often, these claims clashed; since a discoverer was entitled to naming of an element, conflicts over priority of discovery often resulted in conflicts over names of these new elements. These conflicts became known as the Transfermium Wars (fermium is the name of element 100).
Immediately after the fusion, the formed compound nucleus is an excited state; to reach a stable state, it often ejects neutrons which take away the excitation energy. The reactions used in the 1960s resulted in expulsions of four or five neutrons; these started with an element with a high atomic number to maximize the size difference between the two nuclei in a reaction. At JINR, Soviet physicist Yuri Oganessian hypothesized a different mechanism, in which the bombarded nucleus would be lead-208, which has magic numbers of protons and neutrons, or one close to it. The magic number of protons and/or neutrons gives the nuclide additional stability, which requires more energy for an external nucleus to penetrate it. This leaves less excitation energy for the newly created compound nucleus, which necessitates fewer neutron ejections to reach a stable state. This leaves more neutrons in the nucleus, which give the nucleus additional stability, since the neutron–proton ratio of the most stable isotopes grows with the increase of the atomic number.(Due to this energy difference, the former mechanism became known as the "hot fusion" and the latter as "cold fusion".)
Cold fusion was first declared initially successful in 1974 at JINR, when it was tested for synthesis of the yet undiscovered element 106. These new nuclei were projected to decay via spontaneous fission. The physicists at JINR concluded those were not seen before because no then-known fissioning nucleus showed similar parameters of fission and because changing either of the two nuclei in the reactions negated the seen effects. When asked about how far this new method could go and if the lead targets were a physics' Klondike, Oganessian responded, "Klondike may be an exaggeration [...] But soon, we will try to get elements 107...108 in these reactions."
The synthesis of element 108 was first attempted in 1978 by a research team led by Oganessian at the JINR. The team used a reaction that would generate element 108, specifically, the isotope 270108, from fusion of radium (specifically, the isotope 226
) and calcium (48
). The researchers were uncertain in interpreting their data, and their paper did not unambiguously claim to have discovered the element. The same year, another team at JINR investigated the possibility of synthesis of element 108 in reactions between lead (208
) and iron (58
); they were uncertain in interpreting the data, suggesting the possibility that element 108 had not been created.
In 1983, new experiments were performed at JINR. 108; bismuth (209
) was bombarded with manganese (55
) to obtain 263108, lead (207
) was bombarded with iron (58
) to obtain 264108, and californium (249
) was bombarded with neon (22
) to obtain 270108. These experiments were not claimed as a discovery and Oganessian announced them in a conference rather than in a written report.
In 1984, JINR researchers in Dubna performed experiments set up identically to the previous ones; they bombarded bismuth and lead targets with ions of lighter elements manganese and iron, respectively. Twenty-one spontaneous fission events were recorded; these were assigned to 264108.
Later in 1984, a research team led by Peter Armbruster and Gottfried Münzenberg at the GSI attempted to create element 108. The team bombarded a lead (208
) target with accelerated iron (58
) nuclei. GSI's experiment to create element 108 was delayed until after their creation of element 109 in 1982, as prior calculations had suggested that even–even isotopes of element 108 would have spontaneous fission half-lives of less than one microsecond, making them difficult to detect and identify. (A nuclide decaying in less than a microsecond would decay before it reached the detectors, and a nuclide decaying by spontaneous fission rather than alpha emission would be harder to identify.) The element 108 experiment finally went ahead after 266109 had been synthesized and was found to decay by alpha emission, suggesting that isotopes of element 108 would do likewise, and this was corroborated by an experiment aimed at synthesizing isotopes of element 106. GSI reported synthesis of three atoms of 265108. Two years later, they reported synthesis of one atom of the even–even 264108.
In 1985, the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) formed the Transfermium Working Group (TWG) to assess discoveries and establish final names for elements with atomic numbers greater than 100. The party held meetings with delegates from the three competing institutes; in 1990, they established criteria for recognition of an element and in 1991, they finished the work of assessing discoveries and disbanded. These results were published in 1993.
According to the report, the 1984 works from JINR and GSI simultaneously and independently established synthesis of element 108. Of the two 1984 works, the one from GSI was said to be sufficient as a discovery on its own. The JINR work, which preceded the GSI one, "very probably" displayed synthesis of element 108 but that was determined in retrospect given the work from Darmstadt; JINR work had focused on chemically identifying remote granddaughters of element 108 isotopes (which could not exclude the possibility that other ancestors were the source of these daughters), while the GSI work clearly identified the decay path of those element 108 isotopes. The report concluded that the major credit should be awarded to GSI. In written responses to this ruling, both the JINR and GSI agreed with its conclusions. In the same response, GSI proposed a name for element 108 that had been officially presented at the facility three weeks earlier.
Historically, a newly discovered element was named by its discoverer. The first regulation came in 1947, when IUPAC decided that naming required regulation in case there are conflicting names.These matters were to be resolved by the Commission of Inorganic Nomenclature and the Commission of Atomic Weights. They would review the names in case of a conflict and select one; the decision would be based on a number of factors, such as usage, and would not be an indicator of priority of a claim. The two commissions would recommend a name to the IUPAC Council, which would be the final authority. The discoverers held the right to name an element, but their name would be a subject to approval by IUPAC. The Commission of Atomic Weights distanced itself from element naming in most cases.
According to Mendeleev's nomenclature for unnamed and undiscovered elements, hassium should be known as "eka-osmium". In 1979, IUPAC published recommendations according to which the element was to be called "unniloctium" and assigned the corresponding symbol of "Uno", 108", with the symbols E108, (108) or 108, or used the proposed name "hassium".a systematic element name as a placeholder until the element was discovered and the discovery then confirmed, and a permanent name was decided. Although these recommendations were widely followed in the chemical community, most scientists in the field ignored them. They either called it "element
In 1990, in an attempt to break a deadlock in establishing priority of discovery and naming of several elements, IUPAC reaffirmed in its nomenclature of inorganic chemistry that after existence of an element was established, the discoverers could propose a name. (In addition, the Commission of Atomic Weights was excluded from the naming process.) The first publication on criteria for an element discovery, released in 1991, specified the need for recognition by TWG.
Armbruster and his colleagues, the officially recognized German discoverers, held a naming ceremony for the elements 107 through 109, which were all recognized to have been discovered by GSI, on 7 September 1992. For element 108, the scientists proposed the name "hassium". It is derived from the Latin name Hassia for the German state of Hesse where the institute is located. This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.
In 1994, IUPAC Commission on Nomenclature of Inorganic Chemistry recommended that element 108 be named "hahnium" (Hn) after the German physicist Otto Hahn so elements named after Hahn and Lise Meitner (it was recommended element 109 should be named meitnerium) would be next to each other, honouring their joint discovery of nuclear fission; IUPAC commented that they felt the German suggestion was obscure. GSI protested, saying this proposal contradicted the long-standing convention of giving the discoverer the right to suggest a name; the American Chemical Society supported GSI. The name "hahnium", albeit with the different symbol Ha, had already been proposed and used by American scientists for element 105, which they had a discovery dispute with JINR for; they thus protested the confusing scrambling of names. IUPAC relented and the name hassium (Hs) was adopted internationally in 1997. Simultaneously, the name dubnium (Db; from Dubna, the JINR location) was assigned to element 105, and the name hahnium was abandoned.
The official justification for this naming, alongside that of darmstadtium for element 110, was that it completed a set of geographic names for the location of the GSI; this set was initiated by 19th-century names europium and germanium. This set would serve as a response to earlier naming of americium, californium and berkelium for elements discovered in Berkeley. Armbruster commented on this, "this bad tradition was established by Berkeley. We wanted to do it for Europe." Later, when commenting on the naming of element 112, Armbruster said, "I did everything to ensure that we do not continue with German scientists and German towns."
Hassium is not known to occur naturally on Earth; the half-lives of all of its known isotopes are short enough that no primordial hassium would have survived to the present day. This does not rule out the possibility of the existence of unknown, longer-lived isotopes or nuclear isomers, some of which could still exist in trace quantities if they are long-lived enough. As early as 1914, German physicist Richard Swinne proposed element 108 as a source of X-rays in the Greenland ice sheet. Although Swinne was unable to verify this observation and thus did not claim discovery, he proposed in 1931 the existence of regions of long-lived transuranic elements, including one around Z = 108.
In 1963, Soviet geologist and physicist Viktor Cherdyntsev, who had previously claimed the existence of primordial curium-247, 108—specifically the 267108 isotope, which supposedly had a half-life of 400 to 500 million years—in natural molybdenite and suggested the provisional name sergenium (symbol Sg); this name takes its origin from the name for the Silk Road and was explained as "coming from Kazakhstan" for it. His rationale for claiming that sergenium was the heavier homologue to osmium was that minerals supposedly containing sergenium formed volatile oxides when boiled in nitric acid, similarly to osmium.claimed to have discovered element
Cherdyntsev's findings were criticized by Soviet physicist Vladimir Kulakov on the grounds that some of the properties Cherdyntsev claimed sergenium had were inconsistent with the then-current nuclear physics. The chief questions raised by Kulakov were that the claimed alpha decay energy of sergenium was many orders of magnitude lower than expected and the half-life given was eight orders of magnitude shorter than what would be predicted for a nuclide alpha-decaying with the claimed decay energy. At the same time, a corrected half-life in the region of 1016 years would be impossible because it would imply the samples contained about 100 milligrams of sergenium. In 2003, it was suggested that the observed alpha decay with energy 4.5 MeV could be due to a low-energy and strongly enhanced transition between different hyperdeformed states of a hassium isotope around 271Hs, thus suggesting that the existence of superheavy elements in nature was at least possible, although unlikely.
In 2004, the Joint Institute for Nuclear Research conducted a search for natural hassium; this was done underground to avoid interference and false positives from cosmic rays. No results were released, strongly implying no natural hassium was found. The possible extent of primordial hassium on Earth is uncertain; it might only exist in traces or could have completely decayed long ago.
In 2006, Russian geologist Alexei Ivanov hypothesized that an isomer of 271Hs might have a half-life of around (2.5±0.5)×108 years, which would explain the observation of alpha particles with energies of around 4.4 MeV in some samples of molybdenite and osmiridium. This isomer of 271Hs could be produced from the beta decay of 271 Bh and 271 Sg, which, being homologous to rhenium and molybdenum respectively, should occur in molybdenite along with rhenium and molybdenum if they occurred in nature. Because hassium is homologous to osmium, it should occur along with osmium in osmiridium if it occurs in nature. The decay chains of 271Bh and 271Sg are hypothetical and the predicted half-life of this hypothetical hassium isomer is not long enough for any sufficient quantity to remain on Earth. It is possible that more 271Hs may be deposited on the Earth as the Solar System travels through the spiral arms of the Milky Way; this would explain excesses of plutonium-239 found on the ocean floors of the Pacific Ocean and the Gulf of Finland. However, minerals enriched with 271Hs are predicted to have excesses of its daughters uranium-235 and lead-207; they would also have different proportions of elements that are formed during spontaneous fission, such as krypton, zirconium and xenon. The natural occurrence of hassium in minerals such as molybdenite and osmiride is theoretically possible, but very unlikely.
Atomic nuclei show additional stability if they have specific numbers of protons or neutrons called magic numbers. The nuclear shell model describes this as a consequence of closed "shells" of protons and neutrons, whose closures create especially stable configurations. The highest known magic numbers are 82 for protons and 126 for neutrons. This notion is sometimes expanded to include additional numbers between those magic numbers, which also provide some additional stability and indicate closure of "sub-shells". There are various predictions for higher magic numbers; the next doubly magic nucleus (having magic numbers of both protons and neutrons) is expected to lie in the center of the "island of stability", which is theorized to contain longer-lived superheavy nuclides in the vicinity of Z = 110–114 and the predicted magic neutron number N = 184. In 1997, Polish physicist Robert Smolańczuk calculated that the isotope 292Hs may be the most stable superheavy nucleus against alpha decay and spontaneous fission as a consequence of the predicted N = 184 shell closure. As such, it was considered as a candidate to exist in nature. This nucleus, however, is predicted to be very unstable toward beta decay and any beta-stable isotopes of hassium such as 286Hs would be too unstable in the other decay channels to be observed in nature. Indeed, a 2012 search for 292Hs in nature along with its homologue osmium was unsuccessful, setting an upper limit to its abundance at 3×10−15 grams of hassium per gram of osmium.
|263Hs||760 µs||α, SF||2009||208Pb(56Fe,n)|
|264Hs||540 µs||α, SF||1986||207Pb(58Fe,n)|
|265Hs||1.96 ms||α, SF||1984||208Pb(56Fe,n)|
|266Hs||3.02 ms||α, SF||2001||270Ds(—,α)|
Hassium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Twelve isotopes with mass numbers ranging from 263 to 277 (with the exceptions of 272, 274, and 276) have been reported, four of which—hassium-265, -267, -269, and -277—have known metastable states,although that of hassium-277 is unconfirmed. Most of these isotopes decay predominantly through alpha decay; this is the most common for all isotopes for which comprehensive decay characteristics are available, the only exception being hassium-277, which undergoes spontaneous fission. The lightest isotopes, which usually have shorter half-lives, were synthesized by direct fusion between two lighter nuclei and as decay products. The heaviest isotope produced by direct fusion is 271Hs; heavier isotopes have only been observed as decay products of elements with larger atomic numbers.
Theoretical models predict a region of instability for some hassium isotopes to lie around A = 275 and N = 168–170, which is between the predicted neutron shell closures at N = 162 for deformed nuclei and N = 184 for spherical nuclei. Nuclides within this region are predicted to have low fission barrier heights, resulting in short partial half-lives toward spontaneous fission. This prediction is supported by the observed 11 millisecond half-life of 277Hs and that of the neighbouring isobar 277Mt because the expected hindrance factors from the odd nucleon were shown to be much lower than expected. The measured half-lives are even lower than those predicted for the even–even 276Hs and 278Ds, which suggests a gap in stability away from the shell closures and perhaps a weakening of the shell closures in this region.
In 1991, Polish physicists Zygmunt Patyk and Adam Sobiczewski predicted = 162 sub-shell. The syntheses of 269Hs, 270Hs, and 271Hs supports the assignment of N = 162 as a magic number. In particular, the low decay energy for 270Hs matches calculations.that 108 is a proton magic number for deformed nuclei—nuclei that are far from spherical—and 162 is a neutron magic number for deformed nuclei. This means such nuclei are permanently deformed in their ground state but have high, narrow fission barriers to further deformation and hence relatively long life-times to spontaneous fission. Computational prospects for shell stabilisation for 270Hs made it a promising candidate for a deformed doubly magic nucleus. Experimental data from the decay of the darmstadtium isotopes 271Ds and 273Ds provides strong evidence for the magic nature of the N
Various calculations suggest that hassium should be the heaviest group 8 element so far, consistent with the periodic law. Its properties should generally match those expected for a heavier homologue of osmium; as is the case for all 6d metals, a few deviations are expected to arise from relativistic effects.
Very few properties of hassium or its compounds have been measured; this is due to the extremely limited and expensive productionand the fact hassium (and its parents) decays very quickly. A few singular chemistry-related properties properties have been measured, such as enthalpy of adsorption of hassium tetroxide, but properties of the hassium metal remain unknown and only predictions are available.
Relativistic effects on hassium should arise due to the high change of its nuclei, which causes the electrons around the nucleus to move faster—so fast their velocity becomes comparable to the speed of light.There are three main effects: the direct relativistic effect, the indirect relativistic effect, and the spin–orbit splitting.
As atomic number increases, so does the electrostatic attraction between an electron and the nucleus. This causes the velocity of the electron to increase, which leads to an increase its mass. This in turn increases the gravitational attraction between the electron and the nucleus, which leads to contraction of the atomic orbitals, most specifically the s and p1/2 orbitals. Their electrons become more closely attached to the atom and harder to pull from the nucleus. This is the direct relativistic effect.
Since the s and p1/2 orbitals are closer to the nucleus, they take a bigger portion of the electric charge of the nucleus on themselves ("shield" it). This leaves less charge for attraction of the remaining electrons, whose orbitals therefore expand, making them easier to pull from the nucleus. This is the indirect relativistic effect.The combination of the two leads to that the Hs+ ion, compared to a neutron atoms, lacks one 6d electron, rather than a 7s electron. In comparison, Os+ lacks a 6s electron compared to the neutral atom. The ionic radius (in oxidation state +8) of hassium is greater than that of osmium because of the relativistic expansion of the 6p3/2 orbitals, which is the outermost orbital for a hassium ion.
There are several kinds of electronic orbitals, denoted by the letters s, p, d, and f (g orbitals are expected to emerge among elements after element 120). Each of these corresponds to an azimuthal quantum number l: s to 0, p to 1, d to 2, and f to 3. However, as velocities of electrons grow, these numbers l (except for l = 0) change to j = l ± 1/2. For instance, of the six 6p electrons, two become 6p1/2 and four become 6p3/2. This is the spin–orbit splitting.It is, however, most visible with p electrons, which do not play an important role in the chemistry of hassium.
These relativistic effects are responsible for the expected increase of the ionization potential, decrease of the electron affinity, and increase of stability of the +8 oxidation state compared to osmium; without them, the trends would be reversed.Relativistic effects decrease the atomization energies of the compounds of hassium because the spin–orbit splitting of the d orbital lowers the binding energy and because the relativistic effects decrease the ionic character in bonding.
The previous members of group 8 have relatively high melting points: Fe, 1538 °C; Ru, 2334 °C; Os, 3033 °C. Much like them, hassium is predicted to be a solid at room temperature although its melting point has not been precisely calculated. Hassium should crystallize in the hexagonal close-packed structure (c/a = 1.59), similarly to its lighter congener osmium. Pure metallic hassium is calculated to have a bulk modulus (resistance to uniform compression) of 450 GPa, comparable with that of diamond, which has bulk modulus 442 GPa. Hassium is expected to have a bulk density of 41 g/cm3 at standard pressure and temperature, the highest of any of the 118 known elements and nearly twice the highest density of an element observed to this day at 22.6 g/cm3.
The atomic radius of hassium is expected to be around 126 pm. Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Hs+ ion is predicted to have an electron configuration of [ Rn ] 5f14 6d5 7s2, giving up a 6d electron instead of a 7s electron, which is the opposite of the behaviour of its lighter homologues. The Hs2+ ion is expected to have an electron configuration of [Rn] 5f14 6d5 7s1, analogous to that calculated for the Os2+ ion. In chemical compounds, hassium is calculated to display bonding characteristic for a d-block element, whose bonding will be primarily executed by 6d3/2 and 6d5/2 orbitals; compared to the elements from the previous periods, 7s, 6p1/2, 6p3/2, and 7p1/2 orbitals should be more important.
|Element||Stable oxidation states|
Hassium is the sixth member of the 6d series of transition metals and is expected to be much like the platinum group metals. V, which is more than that for the Cu2+/Cu couple of copper (0.3419 V), but less than that for the Ru2+/Ru couple for ruthenium (0.455 V).Some of these properties were confirmed by gas-phase chemistry experiments. The group 8 elements portray a wide variety of oxidation states but ruthenium and osmium readily portray their group oxidation state of +8; this state becomes more stable down the group. This oxidation state is extremely rare: among stable elements, only ruthenium, osmium, and xenon are able to attain it in reasonably stable compounds. Hassium is expected to follow its congeners and have a stable +8 state, but like them it should show other stable, lower oxidation states such as +6, +4, +3, and +2. Hassium(IV) is expected to be more stable than hassium(VIII) in aqueous solution. Hassium should be a rather noble metal; the standard reduction potential for the Hs4+/Hs couple is expected to be 0.4
The group 8 elements show a distinctive oxide chemistry. All of the lighter members have known or hypothetical tetroxides, MO4. FeO2−
4. Ruthenium tetroxide, RuO4, which is formed by oxidation of ruthenium(VI) in acid, readily undergoes reduction to ruthenate(VI), RuO2−
4. Oxidation of ruthenium metal in air forms the dioxide, RuO2. In contrast, osmium burns to form the stable tetroxide, OsO4, which complexes with the hydroxide ion to form an osmium(VIII) -ate complex, [OsO4(OH)2]2−. Therefore, eka-osmium properties for hassium should be demonstrated by the formation of a stable, very volatile tetroxide HsO4, which undergoes complexation with hydroxide to form a hassate(VIII), [HsO4(OH)2]2−. Ruthenium tetroxide and osmium tetroxide are both volatile due to their symmetrical tetrahedral molecular geometry and because they are charge-neutral; hassium tetroxide should similarly be a very volatile solid. The trend of the volatilities of the group 8 tetroxides is known to be RuO4 < OsO4 > HsO4, which confirms the calculated results. In particular, the calculated enthalpies of adsorption—the energy required for the adhesion of atoms, molecules, or ions from a gas, liquid or dissolved solid to a surface—of HsO4, −(45.4 ± 1) kJ/mol on quartz, agrees very well with the experimental value of −(46 ± 2) kJ/mol.
The first goal for chemical investigation was the formation of the tetroxide; it was chosen because ruthenium and osmium form volatile tetroxides, being the only transition metals to display a stable compound in the +8 oxidation state. pb —and thus did not provide enough hassium atoms for a chemical investigation. The direct synthesis of 269Hs and 270Hs in the reaction 248Cm(26Mg,xn)274−xHs (x = 4 or 5) appeared more promising because the cross section for this reaction was somewhat larger at 7 pb. This yield was still around ten times lower than that for the reaction used for the chemical characterization of bohrium. New techniques for irradiation, separation and detection had to be introduced before hassium could be successfully characterized chemically.Despite this selection for gas-phase chemical studies being clear from the beginning, the chemical characterization of hassium was considered a difficult task for a long time. Although hassium isotopes were first synthesized in 1984, it was not until 1996 that a hassium isotope long-lived enough to allow chemical studies to be performed was synthesized. Unfortunately, this hassium isotope, 269Hs, was synthesized indirectly from the decay of 277 Cn; not only are indirect synthesis methods not favourable for chemical studies, but the reaction that produced the isotope 277Cn had a low yield—its cross section was only 1
Ruthenium and osmium have very similar chemistry due to the lanthanide contraction but iron shows some differences from them; for example, although ruthenium and osmium form stable tetroxides in which the metal is in the +8 oxidation state, iron does not.In preparation for the chemical characterization of hassium, research focused on ruthenium and osmium rather than iron because hassium was expected to be similar to ruthenium and osmium, as the predicted data on hassium closely matched that of those two.
The first chemistry experiments were performed using gas thermochromatography in 2001, using 172Os and 173Os as a reference. During the experiment, seven hassium atoms were synthesized using the reactions 248Cm(26Mg,5n)269Hs and 248Cm(26Mg,4n)270Hs. They were then thermalized and oxidized in a mixture of helium and oxygen gases to form hassium tetroxide molecules.
The measured deposition temperature of hassium tetroxide was higher than that of osmium tetroxide, which indicated the former was the less volatile one, and this placed hassium firmly in group 8. −46±2 kJ/mol , was significantly lower than the predicted value, −36.7±1.5 kJ/mol, indicating OsO4 is more volatile than HsO4, contradicting earlier calculations that implied they should have very similar volatilities. For comparison, the value for OsO4 is −39±1 kJ/mol. It is possible hassium tetroxide interacts differently with silicon nitride than with silicon dioxide, the chemicals used for the detector; further research is required, including more accurate measurements of the nuclear properties of 269Hs and comparisons with RuO4 in addition to OsO4.The enthalpy of adsorption for HsO4 measured,
In 2004, scientists reacted hassium tetroxide and sodium hydroxide to form sodium hassate(VIII), a reaction that is well known with osmium. This was the first acid-base reaction with a hassium compound, forming sodium hassate(VIII):
The team from the University of Mainz planned in 2008 to study the electrodeposition of hassium atoms using the new TASCA facility at GSI. Their aim was to use the reaction 226Ra(48Ca,4n)270Hs. As of 2019 [update] , there are no experimental reports of hassocene.Scientists at GSI were hoping to use TASCA to study the synthesis and properties of the hassium(II) compound hassocene, Hs(C5H5)2, using the reaction 226Ra(48Ca,xn). This compound is analogous to the lighter compounds ferrocene, ruthenocene and osmocene, and is expected to have the two cyclopentadienyl rings in an eclipsed conformation like ruthenocene and osmocene and not in a staggered conformation like ferrocene. Hassocene, which is expected to be a stable and highly volatile compound, was chosen because it has hassium in the low formal oxidation state of +2—although the bonding between the metal and the rings is mostly covalent in metallocenes—rather than the high +8 state that had previously been investigated, and relativistic effects were expected to be stronger in the lower oxidation state. Many metals in the periodic table form metallocenes so trends could be more easily determined. The highly symmetrical structure of hassocene and its low number of atoms make relativistic calculations easier.
Bohrium is a synthetic chemical element with the symbol Bh and atomic number 107. It is named after Danish physicist Niels Bohr. As a synthetic element, it can be created in a laboratory but is not found in nature. All known isotopes of bohrium are extremely radioactive; the most stable known isotope is 270Bh with a half-life of approximately 61 seconds, though the unconfirmed 278Bh may have a longer half-life of about 690 seconds.
Dubnium is a synthetic chemical element with the symbol Db and atomic number 105. Dubnium is highly radioactive: the most stable known isotope, dubnium-268, has a half-life of about 28 hours. This greatly limits the extent of research on dubnium.
Meitnerium is a synthetic chemical element with the symbol Mt and atomic number 109. It is an extremely radioactive synthetic element. The most stable known isotope, meitnerium-278, has a half-life of 4.5 seconds, although the unconfirmed meitnerium-282 may have a longer half-life of 67 seconds. The GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany, first created this element in 1982. It is named after Lise Meitner.
The transuranium 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.
Livermorium is a synthetic chemical element with the symbol Lv and has an atomic number of 116. It is an extremely radioactive element that has only been created in the laboratory and has not been observed in nature. The element is named after the Lawrence Livermore National Laboratory in the United States, which collaborated with the Joint Institute for Nuclear Research (JINR) in Dubna, Russia to discover livermorium during experiments made between 2000 and 2006. The name of the laboratory refers to the city of Livermore, California where it is located, which in turn was named after the rancher and landowner Robert Livermore. The name was adopted by IUPAC on May 30, 2012. Four isotopes of livermorium are known, with mass numbers between 290 and 293 inclusive; the longest-lived among them is livermorium-293 with a half-life of about 60 milliseconds. A fifth possible isotope with mass number 294 has been reported but not yet confirmed.
In nuclear physics, the island of stability is a predicted set of isotopes of superheavy elements that may have considerably longer half-lives than known isotopes of these elements. It is predicted to appear as an "island" in the chart of nuclides, separated from known stable and long-lived primordial radionuclides. Its theoretical existence is attributed to stabilizing effects of predicted magic numbers of protons and neutrons in the superheavy mass region.
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 are used until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkaline earth metal, and the second element in the eighth period. It has attracted attention because of some predictions that it may be in the island of stability, although newer calculations expect the island to actually occur at a slightly lower atomic number, closer to copernicium and flerovium.
Ununennium, also known as eka-francium or element 119, is the hypothetical chemical element with symbol Uue and atomic number 119. Ununennium and Uue are the temporary systematic IUPAC name and symbol respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkali metal, and the first element in the eighth period. It is the lightest element that has not yet been synthesized.
Moscovium is a synthetic chemical element with the symbol Mc and atomic number 115. It was first synthesized in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of four new elements by the Joint Working Party of international scientific bodies IUPAC and IUPAP. On 28 November 2016, it was officially named after the Moscow Oblast, in which the JINR is situated.
Tennessine is a synthetic chemical element with the symbol Ts and atomic number 117. It is the second-heaviest known element and the penultimate element of the 7th period of the periodic table.
Copernicium is a synthetic chemical element with the symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 28 seconds. Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the astronomer Nicolaus Copernicus.
An extended periodic table theorises about chemical elements beyond those currently known in the periodic table and proven up through oganesson, which completes the seventh period (row) in the periodic table at atomic number (Z) 118.
Flerovium is a superheavy artificial chemical element with the symbol Fl and atomic number 114. It is an extremely radioactive synthetic element. The element is named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered in 1998. The name of the laboratory, in turn, honours the Russian physicist Georgy Flyorov. The name was adopted by IUPAC on 30 May 2012.
Nihonium is a synthetic chemical element with the symbol Nh and atomic number 113. It is extremely radioactive; its most stable known isotope, nihonium-286, has a half-life of about 10 seconds. In the periodic table, nihonium is a transactinide element in the p-block. It is a member of period 7 and group 13.
In nuclear physics, a magic number is a number of nucleons such that they are arranged into complete shells within the atomic nucleus. The seven most widely recognized magic numbers as of 2019 are 2, 8, 20, 28, 50, 82, and 126. For protons, this corresponds to the elements helium, oxygen, calcium, nickel, tin, lead and the hypothetical unbihexium, although 126 is so far only known to be a magic number for neutrons. Atomic nuclei consisting of such a magic number of nucleons have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay.
Unbibium, also known as element 122 or eka-thorium, is the hypothetical chemical element in the periodic table with the placeholder symbol of Ubb and atomic number 122. Unbibium and Ubb are the temporary systematic IUPAC name and symbol respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table of the elements, it is expected to follow unbiunium as the second element of the superactinides and the fourth element of the 8th period. Similarly to unbiunium, it is expected to fall within the range of the island of stability, potentially conferring additional stability on some isotopes, especially 306Ubb which is expected to have a magic number of neutrons (184).
Hassium (108Hs) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 265Hs in 1984. There are 12 known isotopes from 263Hs to 277Hs and 1–4 isomers. The longest-lived isotope is 269Hs with a half-life of 16 seconds.
Flerovium (114Fl) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 289Fl in 1999. Flerovium has seven known isotopes, and possibly 2 nuclear isomers. The longest-lived isotope is 289Fl with a half-life of 1.9 seconds, but the unconfirmed 290Fl may have a longer half-life of 19 seconds.
Unbiquadium, also known as element 124 or eka-uranium, is the hypothetical chemical element with atomic number 124 and placeholder symbol Ubq. Unbiquadium and Ubq are the temporary IUPAC name and symbol, respectively, until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table, unbiquadium is expected to be a g-block superactinide and the sixth element in the 8th period. Unbiquadium has attracted attention, as it may lie within the island of stability, leading to longer half-lives, especially for 308Ubq which is predicted to have a magic number of neutrons (184).
Unbihexium, also known as element 126 or eka-plutonium, is the hypothetical chemical element with atomic number 126 and placeholder symbol Ubh. Unbihexium and Ubh are the temporary IUPAC name and symbol, respectively, until the element is discovered, confirmed, and a permanent name is decided upon. In the periodic table, unbihexium is expected to be a g-block superactinide and the eighth element in the 8th period. Unbihexium has attracted attention among nuclear physicists, especially in early predictions targeting properties of superheavy elements, for 126 may be a magic number of protons near the center of an island of stability, leading to longer half-lives, especially for 310Ubh or 354Ubh which may also have magic numbers of neutrons.