Unbinilium, also known aseka-radium orelement 120, is a hypotheticalchemical element; it has symbolUbn andatomic number 120.Unbinilium andUbn are the temporarysystematic IUPAC name and symbol respectively, which are used until the element is discovered, confirmed, and a permanent name is decided upon. In theperiodic table of the elements, it is expected to be ans-block element, analkaline earth metal, and the second element in the eighthperiod. It has attracted attention because of some predictions that it may be in theisland of stability.
Unbinilium has not yet been synthesized, despite multiple attempts from German and Russian teams. Experimental evidence from these attempts shows that the period 8 elements would likely be far more difficult to synthesise than the previous known elements. New attempts by American, Russian, and Chinese teams to synthesize unbinilium are planned to begin in the mid-2020s; in particular, an attempt to synthesize the element was ongoing as of September 2025[update], atLawrence Berkeley National Laboratory in the United States.
Unbinilium's position as the seventh alkaline earth metal suggests that it would have similar properties to its lightercongeners; however,relativistic effects may cause some of its properties to differ from those expected from a straight application ofperiodic trends. For example, unbinilium is expected to be less reactive thanbarium andradium, be closer in behavior tostrontium, and while it should show the characteristic +2oxidation state of the alkaline earth metals, it is also predicted to show the +4 and +6 oxidation states, which are unknown in any other alkaline earth metal.
A graphic depiction of anuclear fusion reaction. Two nuclei fuse into one, emitting aneutron. Reactions that created new elements to this moment were similar, with the only possible difference that several singular neutrons sometimes were released, or none at all.
A superheavy[a]atomic nucleus is created in a nuclear reaction that combines two other nuclei of unequal size[b] into one; roughly, the more unequal the two nuclei in terms ofmass, the greater the possibility that the two react.[15] The material made of the heavier nuclei is made into a target, which is then bombarded by thebeam of lighter nuclei. Two nuclei can onlyfuse into one if they approach each other closely enough; normally, nuclei (all positively charged) repel each other due toelectrostatic repulsion. Thestrong interaction can overcome this repulsion but only within a very short distance from a nucleus; beam nuclei are thus greatlyaccelerated in order to make such repulsion insignificant compared to the velocity of the beam nucleus.[16] The energy applied to the beam nuclei to accelerate them can cause them to reach speeds as high as one-tenth of thespeed of light. However, if too much energy is applied, the beam nucleus can fall apart.[16]
Coming close enough alone is not enough for two nuclei to fuse: when two nuclei approach each other, they usually remain together for about 10−20 seconds and then part ways (not necessarily in the same composition as before the reaction) rather than form a single nucleus.[16][17] This happens because during the attempted formation of a single nucleus, electrostatic repulsion tears apart the nucleus that is being formed.[16] Each pair of a target and a beam is characterized by itscross 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.[c] This fusion may occur as a result of the quantum effect in which nuclei cantunnel through electrostatic repulsion. If the two nuclei can stay close past that phase, multiple nuclear interactions result in redistribution of energy and an energy equilibrium.[16]
The resulting merger is anexcited state[20]—termed acompound nucleus—and thus it is very unstable.[16] To reach a more stable state, the temporary merger mayfission without formation of a more stable nucleus.[21] Alternatively, the compound nucleus may eject a fewneutrons, which would carry away the excitation energy; if the latter is not sufficient for a neutron expulsion, the merger would produce agamma ray. This happens in about 10−16 seconds after the initial nuclear collision and results in creation of a more stable nucleus.[21] The definition by theIUPAC/IUPAP Joint Working Party (JWP) states that achemical element can only be recognized as discovered if a nucleus of it has notdecayed within 10−14 seconds. This value was chosen as an estimate of how long it takes a nucleus to acquireelectrons and thus display its chemical properties.[22][d]
The beam passes through the target and reaches the next chamber, the separator; if a new nucleus is produced, it is carried with this beam.[24] In the separator, the newly produced nucleus is separated from other nuclides (that of the original beam and any other reaction products)[e] and transferred to asurface-barrier detector, which stops the nucleus. The exact location of the upcoming impact on the detector is marked; also marked are its energy and the time of the arrival.[24] The transfer takes about 10−6 seconds; in order to be detected, the nucleus must survive this long.[27] The nucleus is recorded again once its decay is registered, and the location, theenergy, and the time of the decay are measured.[24]
Stability of a nucleus is provided by the strong interaction. However, its range is very short; as nuclei become larger, its influence on the outermostnucleons (protons and neutrons) weakens. At the same time, the nucleus is torn apart by electrostatic repulsion between protons, and its range is not limited.[28] Totalbinding energy provided by the strong interaction increases linearly with the number of nucleons, whereas electrostatic repulsion increases with the square of the atomic number, i.e. the latter grows faster and becomes increasingly important for heavy and superheavy nuclei.[29][30] Superheavy nuclei are thus theoretically predicted[31] and have so far been observed[32] to predominantly decay via decay modes that are caused by such repulsion:alpha decay andspontaneous fission.[f] Almost all alpha emitters have over 210 nucleons,[34] and the lightest nuclide primarily undergoing spontaneous fission has 238.[35] In both decay modes, nuclei are inhibited from decaying by correspondingenergy barriers for each mode, but they can be tunneled through.[29][30]
Scheme of an apparatus for creation of superheavy elements, based on the Dubna Gas-Filled Recoil Separator set up in theFlerov Laboratory of Nuclear Reactions in JINR. The trajectory within the detector and the beam focusing apparatus changes because of adipole magnet in the former andquadrupole magnets in the latter.[36]
Alpha particles are commonly produced in radioactive decays because the mass of an alpha particle per nucleon is small enough to leave some energy for the alpha particle to be used as kinetic energy to leave the nucleus.[37] Spontaneous fission is caused by electrostatic repulsion tearing the nucleus apart and produces various nuclei in different instances of identical nuclei fissioning.[30] As the atomic number increases, spontaneous fission rapidly becomes more important: spontaneous fission partial half-lives decrease by 23 orders of magnitude fromuranium (element 92) tonobelium (element 102),[38] and by 30 orders of magnitude fromthorium (element 90) tofermium (element 100).[39] The earlierliquid drop model thus suggested that spontaneous fission would occur nearly instantly due to disappearance of thefission barrier for nuclei with about 280 nucleons.[30][40] The laternuclear shell model suggested that nuclei with about 300 nucleons would form anisland of stability in which nuclei will be more resistant to spontaneous fission and will primarily undergo alpha decay with longer half-lives.[30][40] Subsequent discoveries suggested that the predicted island might be further than originally anticipated; they also showed that nuclei intermediate between the long-lived actinides and the predicted island are deformed, and gain additional stability from shell effects.[41] Experiments on lighter superheavy nuclei,[42] as well as those closer to the expected island,[38] have shown greater than previously anticipated stability against spontaneous fission, showing the importance of shell effects on nuclei.[g]
Alpha decays are registered by the emitted alpha particles, and the decay products are easy 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.[h] (That all decays within a decay chain were indeed related to each other is established by the location of these decays, which must be in the same place.)[24] The known nucleus can be recognized by the specific characteristics of decay it undergoes such as decay energy (or more specifically, thekinetic energy of the emitted particle).[i] Spontaneous fission, however, produces various nuclei as products, so the original nuclide cannot be determined from its daughters.[j]
The information available to physicists aiming to synthesize a superheavy element is thus the information collected at the detectors: location, energy, and time of arrival of a particle to the detector, and those of its decay. The physicists analyze this data and seek to conclude that it was indeed caused by a new element and could not have been caused by a different nuclide than the one claimed. Often, provided data is insufficient for a conclusion that a new element was definitely created and there is no other explanation for the observed effects; errors in interpreting data have been made.[k]
Elements 114 to 118 (flerovium throughoganesson) were discovered in "hot fusion" reactions bombarding the actinidesplutonium throughcalifornium withcalcium-48, a quasi-stable neutron-rich isotope which could be used as a projectile to produce more neutron-rich isotopes of superheavy elements.[53] This cannot easily be continued to elements 119 and 120, because it would require a target of the next actinideseinsteinium andfermium. Tens of milligrams of these would be needed to create such targets, but only micrograms of einsteinium and picograms of fermium have so far been produced.[54] More practical production of further superheavy elements would require bombarding actinides with projectiles heavier than48Ca,[53] but this is expected to be more difficult.[54] Attempts to synthesize elements 119 and 120 push the limits of current technology, due to the decreasingcross sections of the production reactions and their probably shorthalf-lives,[55] expected to be on the order of microseconds.[1][56]
Following their success in obtainingoganesson by the reaction between249Cf and48Ca in 2006, the team at theJoint Institute for Nuclear Research (JINR) inDubna started experiments in March–April 2007 to attempt to create unbinilium with a58Fe beam and a244Pu target.[57][58] The attempt was unsuccessful,[59] and the Russian team planned to upgrade their facilities before attempting the reaction again.[59]
No atoms were detected. The GSI repeated the experiment with higher sensitivity in three separate runs in April–May 2007, January–March 2008, and September–October 2008, all with negative results, reaching a cross section limit of 90 fb.[60]
In 2011, after upgrading their equipment to allow the use of more radioactive targets, scientists at the GSI attempted the rather asymmetrical fusion reaction:[61]
248 96Cm +54 24Cr →302 120Ubn* → no atoms
It was expected that the change in reaction would quintuple the probability of synthesizing unbinilium,[62] as the yield of such reactions is strongly dependent on their asymmetry.[55] Although this reaction is less asymmetric than the249Cf+50Ti reaction, it also creates more neutron-rich unbinilium isotopes that should receive increased stability from their proximity to the shell closure atN = 184.[63] Three signals were observed in May 2011; a possible assignment to299Ubn and its daughters was considered,[64] but could not be confirmed,[65][66][63] and a different analysis suggested that what was observed was simply a random sequence of events.[67]
In August–October 2011, a different team at the GSI using the TASCA facility tried a new, even more asymmetrical reaction:[61][68]
249 98Cf +50 22Ti →299 120Ubn* → no atoms
Because of its asymmetry,[69] the reaction between249Cf and50Ti was predicted to be the most favorable practical reaction for synthesizing unbinilium, though it produces a less neutron-rich isotope of unbinilium than any other reaction studied. No unbinilium atoms were identified.[68]
This reaction was investigated again in April to September 2012 at the GSI. This experiment used a249Bk target and a50Ti beam to produceelement 119, but since249Bk decays to249Cf with a half-life of about 327 days, both elements 119 and 120 could be searched for simultaneously:
249 97Bk +50 22Ti →299 119Uue* → no atoms
249 98Cf +50 22Ti →299 120Ubn* → no atoms
Neither element 119 nor element 120 was observed.[70]
The team at theLawrence Berkeley National Laboratory (LBNL) inBerkeley,California, United States had made plans to use the 88-inch cyclotron to make new elements using50Ti projectiles.[54] (Such a plan had already been made before theRussian invasion of Ukraine began in 2022, cutting off collaborations between the JINR and other institutes, in response to theoretical predictions that an attempt to produce element 120 would be feasible.)[71] First, the244Pu+50Ti reaction was tested, successfully creating two atoms of290Lv in 2024. Since this was successful, an attempt to make element 120 in the249Cf+50Ti reaction was planned to begin in late 2025.[72][73][74][75] TheLawrence Livermore National Laboratory (LLNL), which previously collaborated with the JINR, will collaborate with the LBNL on this project.[71] By June 2025, updates were underway at the LBNL in preparation for the search for element 120,[76][77] and by September, the search had begun.[78]
The JINR's plans to investigate the249Cf+50Ti reaction in their new facility were disrupted by the 2022 Russian invasion of Ukraine, after which collaboration between the JINR and other institutes completely ceased due to sanctions. Thus,249Cf could no longer be used as a target, as it would have to be produced at theOak Ridge National Laboratory (ORNL) in the United States.[79][80][81] Instead, the248Cm+54Cr reaction will be used.[82] In 2023, the director of the JINR,Grigory Trubnikov, stated that he hoped that the experiments to synthesise element 120 will begin in 2025.[83] In preparation for this, the JINR reported success in the238U+54Cr reaction in late 2023, making a new isotope of livermorium,288Lv. This was an unexpectedly good result; the aim had been to experimentally determine the cross-section of a reaction with54Cr projectiles and prepare for the synthesis of element 120. It is the first successful reaction producing a superheavy element using an actinide target and a projectile heavier than48Ca.[84]
The team at the Heavy Ion Research Facility inLanzhou, which is operated by theInstitute of Modern Physics (IMP) of theChinese Academy of Sciences, also plans to synthesise elements 119 and 120. The reactions used will involve actinide targets (e.g.243Am,248Cm) and first-row transition metal projectiles (e.g.50Ti,51V,54Cr,55Mn).[85]
Mendeleev's nomenclature for unnamed and undiscovered elements would call unbiniliumeka-radium.[86] The 1979 IUPACrecommendationstemporarily call itunbinilium (symbolUbn) until it is discovered, the discovery is confirmed and a permanent name chosen.[87] Although the IUPAC systematic names are widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, scientists who work theoretically or experimentally on superheavy elements typically call it "element 120", with the symbolE120,(120) or120.[1]
A chart of nuclide stability as used by the Dubna team in 2010. Characterized isotopes are shown with borders. Beyond element 118 (oganesson, the last known element), the line of known nuclides is expected to rapidly enter a region of instability. The elliptical region encloses the predicted location of the island of stability, centered on element 112,copernicium.[55]Orbitals with highazimuthal quantum number are raised in energy, eliminating what would otherwise be a gap in orbital energy corresponding to a closed proton shell at element 114, as shown in the left diagram which does not take this effect into account. This raises the next proton shell to the region around element 120, as shown in the right diagram, potentially increasing the half-lives of element 119 and 120 isotopes.[88]
The stability of nuclei decreases greatly with the increase in atomic number aftercurium, element 96, whose half-life is four orders of magnitude longer than that of any currently known higher-numbered element. All isotopes with an atomic number above101 undergoradioactive decay with half-lives of less than 30 hours. No elements with atomic numbers above 82 (afterlead) have stable isotopes.[89] Nevertheless, because of reasons not yet well understood, there is a slight increase of nuclear stability around atomic numbers110–114, which leads to the appearance of what is known in nuclear physics as the "island of stability". This concept, proposed byUniversity of California professorGlenn Seaborg, explains why superheavy elements last longer than predicted.[90]
Isotopes of unbinilium are predicted to have alpha decay half-lives of the order ofmicroseconds.[91][92] In aquantum tunneling model with mass estimates from a macroscopic-microscopic model, thealpha-decay half-lives of several unbiniliumisotopes (292–304Ubn) have been predicted to be around 1–20 microseconds.[91][93][94][92] Some heavier isotopes may be more stable; Fricke and Waber predicted320Ubn to be the most stable unbinilium isotope in 1971.[3] Since unbinilium is expected to decay via a cascade of alpha decays leading tospontaneous fission aroundcopernicium, the total half-lives of unbinilium isotopes are also predicted to be measured in microseconds.[1][56] This has consequences for the synthesis of unbinilium, as isotopes with half-lives below one microsecond would decay before reaching the detector.[1][56] Nevertheless, new theoretical models show that the expected gap in energy between theproton orbitals 2f7/2 (filled at element 114) and 2f5/2 (filled at element 120) is smaller than expected, so that element 114 no longer appears to be a stable spherical closed nuclear shell, and this energy gap may increase the stability of elements 119 and 120. The nextdoubly magic nucleus is now expected to be around the spherical306Ubb (element 122), but the expected low half-life and low productioncross section of this nuclide makes its synthesis challenging.[88]
Given that element 120 fills the 2f5/2 proton orbital, much attention has been given to the compound nucleus302Ubn* and its properties. Several experiments have been performed between 2000 and 2008 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus302Ubn*. Two nuclear reactions have been used, namely244Pu+58Fe and238U+64Ni. The results have revealed how nuclei such as this fission predominantly by expelling closed shell nuclei such as132Sn (Z = 50,N = 82). It was also found that the yield for the fusion-fission pathway was similar between48Ca and58Fe projectiles, suggesting a possible future use of58Fe projectiles in superheavy element formation.[95]
In 2008, the team atGANIL, France, described the results from a new technique which attempts to measure the fissionhalf-life of a compound nucleus at high excitation energy, since the yields are significantly higher than from neutron evaporation channels. It is also a useful method for probing the effects of shell closures on the survivability of compound nuclei in the super-heavy region, which can indicate the exact position of the next proton shell (Z = 114, 120, 124, or 126). The team studied the nuclear fusion reaction between uranium ions and a target of natural nickel:[96][97]
The results indicated that nuclei of unbinilium were produced at high (≈70 MeV) excitation energy which underwent fission with measurable half-lives just over 10−18 s.[96][97] Although very short (indeed insufficient for the element to be considered byIUPAC to exist, because a compound nucleus has no internal structure and its nucleons have not been arranged into shells until it has survived for 10−14 s, when it forms an electronic cloud),[98] the ability to measure such a process indicates a strong shell effect atZ = 120. At lower excitation energy (see neutron evaporation), the effect of the shell will be enhanced and ground-state nuclei can be expected to have relatively long half-lives. This result could partially explain the relatively long half-life of294Og measured in experiments at Dubna. Similar experiments have indicated a similar phenomenon atelement 124 but not forflerovium, suggesting that the next proton shell does in fact lie beyond element 120.[96][97] In September 2007, the team at RIKEN began a program utilizing248Cm targets and have indicated future experiments to probe the possibility of 120 being the next proton magic number (and 184 being the next neutron magic number) using the aforementioned nuclear reactions to form302Ubn*, as well as248Cm+54Cr. They also planned to further chart the region by investigating the nearby compound nuclei296Og*,298Og*,306Ubb*, and308Ubb*.[99]
The most likely isotopes of unbinilium to be synthesised in the near future are295Ubn through299Ubn, because they can be produced in the 3n and 4n channels of the249–251Cf+50Ti,245Cm+54Cr, and248Cm+54Cr reactions.[100]
Being the secondperiod 8 element, unbinilium is predicted to be an alkaline earth metal, belowberyllium,magnesium,calcium,strontium,barium, andradium. Each of these elements has twovalence electrons in the outermost s-orbital (valence electron configurationns2), which is easily lost in chemical reactions to form the +2oxidation state: thus the alkaline earth metals are ratherreactive elements, with the exception of beryllium due to its small size. Unbinilium is predicted to continue the trend and have a valence electron configuration of 8s2. It is therefore expected to behave much like its lightercongeners; however, it is also predicted to differ from the lighter alkaline earth metals in some properties.[1]
The main reason for the predicted differences between unbinilium and the other alkaline earth metals is thespin–orbit (SO) interaction—the mutual interaction between the electrons' motion andspin. The SO interaction is especially strong for the superheavy elements because their electrons move faster—at velocities comparable to thespeed of light—than those in lighter atoms.[4] In unbinilium atoms, it lowers the 7p and 8s electron energy levels, stabilizing the corresponding electrons, but two of the 7p electron energy levels are more stabilized than the other four.[101] The effect is called subshell splitting, as it splits the 7p subshell into more-stabilized and the less-stabilized parts. Computational chemists understand the split as a change of the second (azimuthal)quantum numberl from 1 to 1/2 and 3/2 for the more-stabilized and less-stabilized parts of the 7p subshell, respectively.[4][l] Thus, the outer 8s electrons of unbinilium are stabilized and become harder to remove than expected, while the 7p3/2 electrons are correspondingly destabilized, perhaps allowing them to participate in chemical reactions.[1] This stabilization of the outermost s-orbital (already significant in radium) is the key factor affecting unbinilium's chemistry, and causes all the trends for atomic and molecular properties of alkaline earth metals to reverse direction after barium.[102]
Empirical (Na–Cs, Mg–Ra) and predicted (Fr–Uhp, Ubn–Uhh) atomic radii of the alkali and alkaline earth metals from thethird to theninth period, measured inangstroms[1][103]
Empirical (Na–Fr, Mg–Ra) and predicted (Uue–Uhp, Ubn–Uhh) ionization energy of the alkali and alkaline earth metals from the third to the ninth period, measured in electron volts[1][103]
Due to the stabilization of its outer 8s electrons, unbinilium's firstionization energy—the energy required to remove an electron from a neutral atom—is predicted to be 6.0 eV, comparable to that of calcium.[1] The electron of thehydrogen-like unbinilium atom—oxidized so it has only one electron, Ubn119+—is predicted to move so quickly that its mass is 2.05 times that of a non-moving electron, a feature coming from therelativistic effects. For comparison, the figure for hydrogen-like radium is 1.30 and the figure for hydrogen-like barium is 1.095.[4] According to simple extrapolations of relativity laws, that indirectly indicates the contraction of theatomic radius[4] to around 200 pm,[1] very close to that of strontium (215 pm); theionic radius of the Ubn2+ ion is also correspondingly lowered to 160 pm.[1] The trend in electron affinity is also expected to reverse direction similarly at radium and unbinilium.[102]
Unbinilium should be asolid at room temperature, with melting point 680 °C:[104] this continues the downward trend down the group, being lower than the value 700 °C for radium.[105] The boiling point of unbinilium is expected to be around 1700 °C, which is lower than that of all the previous elements in the group (in particular, radium boils at 1737 °C), following the downward periodic trend.[3] The density of unbinilium has been predicted to be 7 g/cm3, continuing the trend of increasing density down the group: the value for radium is 5.5 g/cm3.[3][2]
Bond lengths and bond-dissociation energies of alkaline earth metal dimers. Data for Ba2, Ra2 and Ubn2 is predicted.[102]
Compound
Bond length (Å)
Bond-dissociation energy (eV)
Ca2
4.277
0.14
Sr2
4.498
0.13
Ba2
4.831
0.23
Ra2
5.19
0.11
Ubn2
5.65
0.02
The chemistry of unbinilium is predicted to be similar to that of the alkaline earth metals,[1] but it would probably behave more like calcium or strontium[1] than barium or radium. Like strontium, unbinilium should react vigorously with air to form an oxide (UbnO) and with water to form the hydroxide (Ubn(OH)2), which would be a strongbase, and releasinghydrogen gas. It should also react with thehalogens to form salts such as UbnCl2.[106] While these reactions would be expected fromperiodic trends, their lowered intensity is somewhat unusual, as ignoring relativistic effects, periodic trends would predict unbinilium to be even more reactive than barium or radium. This loweredreactivity is due to the relativistic stabilization of unbinilium's valence electron, increasing unbinilium's first ionization energy and decreasing themetallic andionic radii;[107] this effect is already seen for radium.[1] On the other hand, the ionic radius of the Ubn2+ ion is predicted to be larger than that of Sr2+, because the 7p orbitals are destabilized and are thus larger than the p-orbitals of the lower shells.[4]
Unbinilium may also show the +4oxidation state,[1] which is not seen in any other alkaline earth metal,[108] in addition to the +2 oxidation state that is characteristic of the other alkaline earth metals and is also the main oxidation state of all the known alkaline earth metals: this is because of the destabilization and expansion of the 7p3/2 spinor, causing its outermost electrons to have a lower ionization energy than what would otherwise be expected.[1][108] The +6 state involving all the 7p3/2 electrons has been suggested in ahexafluoride, UbnF6.[109] The +1 state may also be isolable.[4] Many unbinilium compounds are expected to have a largecovalent character, due to the involvement of the 7p3/2 electrons in the bonding: this effect is also seen to a lesser extent in radium, which shows some 6s and 6p3/2 contribution to the bonding inradium fluoride (RaF2) and astatide (RaAt2), resulting in these compounds having more covalent character.[4] Thestandard reduction potential of the Ubn2+/Ubn couple is predicted to be −2.9 V, which is almost exactly the same as that for the Sr2+/Sr couple of strontium (−2.899 V).[104]
Bond lengths and bond-dissociation energies of MAu (M = an alkaline earth metal). All data is predicted, except for CaAu.[102]
Compound
Bond length (Å)
Bond-dissociation energy (kJ/mol)
CaAu
2.67
2.55
SrAu
2.808
2.63
BaAu
2.869
3.01
RaAu
2.995
2.56
UbnAu
3.050
1.90
In the gas phase, the alkaline earth metals do not usually form covalently bonded diatomic molecules like the alkali metals do, since such molecules would have the same number of electrons in the bonding and antibonding orbitals and would have very lowdissociation energies.[110] Thus, the M–M bonding in these molecules is predominantly throughvan der Waals forces.[102] The metal–metalbond lengths in these M2 molecules increase down the group from Ca2 to Ubn2. On the other hand, their metal–metalbond-dissociation energies generally increase from Ca2 to Ba2 and then drop to Ubn2, which should be the most weakly bound of all the group 2 homodiatomic molecules. The cause of this trend is the increasing participation of the p3/2 and d electrons as well as the relativistically contracted s orbital.[102] From these M2 dissociation energies, theenthalpy of sublimation (ΔHsub) of unbinilium is predicted to be 150 kJ/mol.[102]
Bond lengths, harmonic frequency, vibrational anharmonicity and bond-dissociation energies of MH and MAu (M = an alkaline earth metal). Data for UbnH and UbnAu are predicted.[111] Data for BaH is taken from experiment,[112] except bond-dissociation energy.[111] Data for BaAu is taken from experiment,[113] except bond-dissociation energy and bond length.[111]
Compound
Bond length (Å)
Harmonic frequency, cm−1
Vibrational anharmonicity, cm−1
Bond-dissociation energy (eV)
UbnH
2.38
1070
20.1
1.00
BaH
2.23
1168
14.5
2.06
UbnAu
3.03
100
0.13
1.80
BaAu
2.91
129
0.18
2.84
The Ubn–Au bond should be the weakest of all bonds between gold and an alkaline earth metal, but should still be stable. This gives extrapolated medium-sized adsorption enthalpies (−ΔHads) of 172 kJ/mol on gold (the radium value should be 237 kJ/mol) and 50 kJ/mol onsilver, the smallest of all the alkaline earth metals, that demonstrate that it would be feasible to study thechromatographicadsorption of unbinilium onto surfaces made ofnoble metals.[102] The ΔHsub and −ΔHads values are correlated for the alkaline earth metals.[102]
^Innuclear physics, an element is calledheavy if its atomic number is high;lead (element 82) is one example of such a heavy element. The term "superheavy elements" typically refers to elements with atomic number greater than103 (although there are other definitions, such as atomic number greater than100[10] or112;[11] sometimes, the term is presented an equivalent to the term "transactinide", which puts an upper limit before the beginning of the hypotheticalsuperactinide series).[12] Terms "heavy isotopes" (of a given element) and "heavy nuclei" mean what could be understood in the common language—isotopes of high mass (for the given element) and nuclei of high mass, respectively.
^In 2009, a team at the JINR led by Oganessian published results of their attempt to create hassium in a symmetric136Xe + 136Xe reaction. They failed to observe a single atom in such a reaction, putting the upper limit on the cross section, the measure of probability of a nuclear reaction, as 2.5 pb.[13] In comparison, the reaction that resulted in hassium discovery,208Pb +58Fe, had a cross section of ~20 pb (more specifically, 19+19 -11 pb), as estimated by the discoverers.[14]
^The amount of energy applied to the beam particle to accelerate it can also influence the value of cross section. For example, in the28 14Si +1 0n →28 13Al +1 1p reaction, cross section changes smoothly from 370 mb at 12.3 MeV to 160 mb at 18.3 MeV, with a broad peak at 13.5 MeV with the maximum value of 380 mb.[18]
^This figure also marks the generally accepted upper limit for lifetime of a compound nucleus.[23]
^This separation is based on that the resulting nuclei move past the target more slowly then the unreacted beam nuclei. The separator contains electric and magnetic fields whose effects on a moving particle cancel out for a specific velocity of a particle.[25] Such separation can also be aided by atime-of-flight measurement and a recoil energy measurement; a combination of the two may allow to estimate the mass of a nucleus.[26]
^It was already known by the 1960s that ground states of nuclei differed in energy and shape as well as that certain magic numbers of nucleons corresponded to greater stability of a nucleus. However, it was assumed that there was no nuclear structure in superheavy nuclei as they were too deformed to form one.[38]
^Since mass of a nucleus is not measured directly but is rather calculated from that of another nucleus, such measurement is called indirect. Direct measurements are also possible, but for the most part they have remained unavailable for superheavy nuclei.[43] The first direct measurement of mass of a superheavy nucleus was reported in 2018 at LBNL.[44] Mass was determined from the location of a nucleus after the transfer (the location helps determine its trajectory, which is linked to the mass-to-charge ratio of the nucleus, since the transfer was done in presence of a magnet).[45]
^If the decay occurred in a vacuum, then since total momentum of an isolated system before and after the decaymust be preserved, the daughter nucleus would also receive a small velocity. The ratio of the two velocities, and accordingly the ratio of the kinetic energies, would thus be inverse to the ratio of the two masses. The decay energy equals the sum of the known kinetic energy of the alpha particle and that of the daughter nucleus (an exact fraction of the former).[34] The calculations hold for an experiment as well, but the difference is that the nucleus does not move after the decay because it is tied to the detector.
^Spontaneous fission was discovered by Soviet physicistGeorgy Flerov,[46] a leading scientist at JINR, and thus it was a "hobbyhorse" for the facility.[47] In contrast, the LBL scientists believed fission information was not sufficient for a claim of synthesis of an element. They believed spontaneous fission had not been studied enough to use it for identification of a new element, since there was a difficulty of establishing that a compound nucleus had only ejected neutrons and not charged particles like protons or alpha particles.[23] They thus preferred to link new isotopes to the already known ones by successive alpha decays.[46]
^For instance, element 102 was mistakenly identified in 1957 at the Nobel Institute of Physics inStockholm,Stockholm County,Sweden.[48] There were no earlier definitive claims of creation of this element, and the element was assigned a name by its Swedish, American, and British discoverers,nobelium. It was later shown that the identification was incorrect.[49] The following year, RL was unable to reproduce the Swedish results and announced instead their synthesis of the element; that claim was also disproved later.[49] JINR insisted that they were the first to create the element and suggested a name of their own for the new element,joliotium;[50] the Soviet name was also not accepted (JINR later referred to the naming of the element 102 as "hasty").[51] This name was proposed to IUPAC in a written response to their ruling on priority of discovery claims of elements, signed 29 September 1992.[51] The name "nobelium" remained unchanged on account of its widespread usage.[52]
^The quantum number corresponds to the letter in the electron orbital name: 0 to s, 1 to p, 2 to d, etc. Seeazimuthal quantum number for more information.
^abcdefghijklmnopqrstuvHoffman, Darleane C.; Lee, Diana M.; Pershina, Valeria (2006). "Transactinides and the future elements". In Morss; Edelstein, Norman M.; Fuger, Jean (eds.).The Chemistry of the Actinide and Transactinide Elements (3rd ed.). Dordrecht, The Netherlands:Springer Science+Business Media.ISBN978-1-4020-3555-5.
^abcdefghThayer, John S. (2010). "Relativistic Effects and the Chemistry of the Heavier Main Group Elements".Relativistic Methods for Chemists. Challenges and Advances in Computational Chemistry and Physics. Vol. 10. p. 84.doi:10.1007/978-1-4020-9975-5_2.ISBN978-1-4020-9974-8.
^Pershina, V.; Borschevsky, A.; Anton, J. (2012). "Theoretical predictions of properties of group-2 elements including element 120 and their adsorption on noble metal surfaces".The Journal of Chemical Physics.136 (134317).Bibcode:2012JChPh.136m4317P.doi:10.1063/1.3699232. This article gives the Mulliken electronegativity as 2.862, which has been converted to the Pauling scale via χP = 1.35χM1/2 − 1.37.
^Pershina, Valeria. "Theoretical Chemistry of the Heaviest Elements". In Schädel, Matthias; Shaughnessy, Dawn (eds.).The Chemistry of Superheavy Elements (2nd ed.). Springer Science & Business Media. p. 154.ISBN9783642374661.
^"Популярная библиотека химических элементов. Сиборгий (экавольфрам)" [Popular library of chemical elements. Seaborgium (eka-tungsten)].n-t.ru (in Russian). Retrieved2020-01-07. Reprinted from"Экавольфрам" [Eka-tungsten].Популярная библиотека химических элементов. Серебро – Нильсборий и далее [Popular library of chemical elements. Silver through nielsbohrium and beyond] (in Russian).Nauka. 1977.
^Hofmann, S.; Heinz, S.; Mann, R.; et al. (2016). "Remarks on the Fission Barriers of SHN and Search for Element 120". In Peninozhkevich, Yu. E.; Sobolev, Yu. G. (eds.).Exotic Nuclei: EXON-2016 Proceedings of the International Symposium on Exotic Nuclei. Exotic Nuclei. pp. 155–164.ISBN978-981-322-655-5.
^Heßberger, F. P.; Ackermann, D. (2017). "Some critical remarks on a sequence of events interpreted to possibly originate from a decay chain of an element 120 isotope".The European Physical Journal A.53 (123): 123.Bibcode:2017EPJA...53..123H.doi:10.1140/epja/i2017-12307-5.S2CID125886824.
^Mayer, Anastasiya (31 May 2023).""Большинство наших партнеров гораздо мудрее политиков"" ["Most of our partners are much wiser than politicians"].Vedomosti (in Russian). Retrieved15 August 2023.В этом году мы фактически завершаем подготовительную серию экспериментов по отладке всех режимов ускорителя и масс-спектрометров для синтеза 120-го элемента. Научились получать высокие интенсивности ускоренного хрома и титана. Научились детектировать сверхтяжелые одиночные атомы в реакциях с минимальным сечением. Теперь ждем, когда закончится наработка материала для мишени на реакторах и сепараторах у наших партнеров в «Росатоме» и в США: кюрий, берклий, калифорний. Надеюсь, что в 2025 г. мы полноценно приступим к синтезу 120-го элемента.
^"В ЛЯР ОИЯИ впервые в мире синтезирован ливерморий-288" [Livermorium-288 was synthesized for the first time in the world at FLNR JINR] (in Russian). Joint Institute for Nuclear Research. 23 October 2023. Retrieved18 November 2023.
^Gan, Z. G.; Huang, W. X.; Zhang, Z. Y.; Zhou, X. H.; Xu, H. S. (2022). "Results and perspectives for study of heavy and super-heavy nuclei and elements at IMP/CAS".The European Physical Journal A.58 (158) 158.Bibcode:2022EPJA...58..158G.doi:10.1140/epja/s10050-022-00811-w.
^Lide, D. R., ed. (2005).CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton, Florida: CRC Press.ISBN0-8493-0486-5.
^Emsley, John (2011).Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. p. 586.ISBN978-0-19-960563-7.
^Knight, L. B.; Easley, W. C.; Weltner, W.; Wilson, M. (January 1971). "Hyperfine Interaction and Chemical Bonding in MgF, CaF, SrF, and BaF molecules".The Journal of Chemical Physics.54 (1):322–329.Bibcode:1971JChPh..54..322K.doi:10.1063/1.1674610.ISSN0021-9606.
^Constants of Diatomic Molecules. New York: Van Nostrand-Reinhold. 1979.
Visualization of unsuccessful nuclear fusion, based on calculations from theAustralian National University[19]
