Flerovium is a superheavy artificial chemical element with 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 (Флёров in Cyrillic, hence the transliteration of "yo" to "e"). The name was adopted by IUPAC on 30 May 2012.

In the periodic table of the elements, it is a transactinide element in the p-block. It is a member of the 7th period and is the heaviest known member of the carbon group; it is also the heaviest element whose chemistry has been investigated. Initial chemical studies performed in 2007–2008 indicated that flerovium was unexpectedly volatile for a group 14 element;[17] in preliminary results it even seemed to exhibit properties similar to those of the noble gases.[18] More recent results show that flerovium's reaction with gold is similar to that of copernicium, showing that it is a very volatile element that may even be gaseous at standard temperature and pressure, that it would show metallic properties, consistent with it being the heavier homologue of lead, and that it would be the least reactive metal in group 14. The question of whether flerovium behaves more like a metal or a noble gas is still unresolved as of 2018.

About 90 atoms of flerovium have been observed: 58 were synthesized directly, and the rest were made from the radioactive decay of heavier elements. All of these flerovium atoms have been shown to have mass numbers from 284 to 290. The most stable known flerovium isotope, flerovium-289, has a half-life of around 2.6 seconds, but it is possible that the unconfirmed flerovium-290 with one extra neutron may have a longer half-life of 19 seconds; this would be one of the longest half-lives of any isotope of any element at these farthest reaches of the periodic table. Flerovium is predicted to be near the centre of the theorized island of stability, and it is expected that heavier flerovium isotopes, especially the possibly doubly magic flerovium-298, may have even longer half-lives.

Flerovium,  114Fl
Pronunciation/flɪˈroʊviəm/[1] (flə-ROH-vee-əm)
Mass number289 (most stable isotope) (unconfirmed: 290)
Flerovium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)114
Groupgroup 14 (carbon group)
Periodperiod 7
Element category  unknown chemical properties, but probably a post-transition metal
Electron configuration[Rn] 5f14 6d10 7s2 7p2 (predicted)[2]
Electrons per shell
2, 8, 18, 32, 32, 18, 4 (predicted)
Physical properties
Phase at STPunknown phase (predicted)[2]
Boiling point~ 210 K ​(~ −60 °C, ​~ −80 °F) [3][4]
Density when liquid (at m.p.)14 g/cm3 (predicted)[5]
Heat of vaporization38 kJ/mol (predicted)[5]
Atomic properties
Oxidation states(0), (+1), (+2), (+4), (+6) (predicted)[2][5][6]
Ionization energies
  • 1st: 832.2 kJ/mol (predicted)[7]
  • 2nd: 1600 kJ/mol (predicted)[5]
  • 3rd: 3370 kJ/mol (predicted)[5]
  • (more)
Atomic radiusempirical: 180 pm (predicted)[2][5]
Covalent radius171–177 pm (extrapolated)[8]
Other properties
Natural occurrencesynthetic
Crystal structureface-centred cubic (fcc)
Face-centred cubic crystal structure for flerovium

CAS Number54085-16-4
Namingafter Flerov Laboratory of Nuclear Reactions (itself named after Georgy Flyorov)[10]
DiscoveryJoint Institute for Nuclear Research (JINR) and Lawrence Livermore National Laboratory (LLNL) (1999)
Main isotopes of flerovium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
284Fl[11][12] syn 2.5 ms SF
285Fl[13] syn 0.10 s α 281Cn
286Fl syn 0.12 s 40% α 282Cn
60% SF
287Fl[14] syn 0.48 s α 283Cn
EC? 287Nh
288Fl syn 0.66 s α 284Cn
289Fl syn 1.9 s α 285Cn
290Fl[15][16] syn 19 s? EC 290Nh
α 286Cn



From the late 1940s to the early 1960s, the early days of the synthesis of heavier and heavier transuranium elements, it was predicted that since such heavy elements did not occur naturally, they would have shorter and shorter half-lives to spontaneous fission, until they stopped existing altogether at around element 108 (now known as hassium). Initial work in the synthesis of the actinides appeared to confirm this.[19] The nuclear shell model, introduced in the late 1960s, stated that the protons and neutrons formed shells within a nucleus, somewhat analogous to electrons forming electron shells within an atom. The noble gases are unreactive due to their having full electron shells; thus it was theorized that elements with full nuclear shells – having so-called "magic" numbers of protons or neutrons – would be stabilized against radioactive decay. A doubly magic isotope, having magic numbers of both protons and neutrons, would be especially stabilized, and it was calculated that the next doubly magic isotope after lead-208 would be flerovium-298 with 114 protons and 184 neutrons, which would form the centre of a so-called "island of stability".[19] This island of stability, supposedly ranging from copernicium (element 112) to oganesson (118), would come after a long "sea of instability" from elements 101 (mendelevium) to 111 (roentgenium),[19] and the flerovium isotopes in it were speculated in 1966 to have half-lives in excess of a hundred million years.[20] These early predictions fascinated researchers, and led to the first attempted synthesis of flerovium in 1968 using the reaction 248Cm(40Ar,xn). No isotopes of flerovium were found in this reaction. This was thought to occur because the compound nucleus 288Fl only has 174 neutrons instead of the hypothesized magic 184, and this would have a significant impact on the half-life and cross section of such a reaction.[21][22] It then took thirty more years for the first isotopes of flerovium to be synthesized.[19] More recent work suggests that the local islands of stability around hassium and flerovium are due to these nuclei being respectively deformed and oblate, which make them resistant to spontaneous fission, and that the true island of stability for spherical nuclei occurs at around unbibium-306 (with 122 protons and 184 neutrons).[23]


Flerovium was first synthesized in December 1998 by a team of scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, led by Yuri Oganessian, who bombarded a target of plutonium-244 with accelerated nuclei of calcium-48:

+ 48
* → 290
+ 2 1

This reaction had been attempted before, but without success; for this 1998 attempt, the JINR had upgraded all of its equipment to detect and separate the produced atoms better and bombard the target more intensely.[24] A single atom of flerovium, decaying by alpha emission with a lifetime of 30.4 seconds, was detected. The decay energy measured was 9.71 MeV, giving an expected half-life of 2–23 s.[25] This observation was assigned to the isotope flerovium-289 and was published in January 1999.[25] The experiment was later repeated, but an isotope with these decay properties was never found again and hence the exact identity of this activity is unknown. It is possible that it was due to the metastable isomer 289mFl,[26][27] but because the presence of a whole series of longer-lived isomers in its decay chain would be rather doubtful, the most likely assignment of this chain is to the 2n channel leading to 290Fl and electron capture to 290Nh, which fits well with the systematics and trends across flerovium isotopes, and is consistent with the low beam energy that was chosen for that experiment, although further confirmation would be desirable via the synthesis of 294Lv in the 248Cm(48Ca,2n) reaction, which would alpha decay to 290Fl.[15] The team at RIKEN reported a possible synthesis of the isotopes 294Lv and 290Fl in 2016 through the 248Cm(48Ca,2n) reaction, but the alpha decay of 294Lv was missed, alpha decay of 290Fl to 286Cn was observed instead of electron capture to 290Nh, and the assignment to 294Lv instead of 293Lv and decay to an isomer of 285Cn was not certain.[16]

Glenn T. Seaborg, a scientist at the Lawrence Berkeley National Laboratory who had been involved in work to synthesize such superheavy elements, had said in December 1997 that "one of his longest-lasting and most cherished dreams was to see one of these magic elements";[19] he was told of the synthesis of flerovium by his colleague Albert Ghiorso soon after its publication in 1999. Ghiorso later recalled:[28]

I wanted Glenn to know, so I went to his bedside and told him. I thought I saw a gleam in his eye, but the next day when I went to visit him he didn't remember seeing me. As a scientist, he had died when he had that stroke.[28]

— Albert Ghiorso

Seaborg died 2 months later, on 25 February 1999.[28]

Road to confirmation

In March 1999, the same team replaced the 244Pu target with a 242Pu one in order to produce other flerovium isotopes. This time two atoms of flerovium were produced, decaying via alpha emission with a half-life of 5.5 s. They were assigned as 287Fl.[29] This activity has not been seen again either, and it is unclear what nucleus was produced. It is possible that it was the meta-stable isomer 287mFl[30] or the result of an electron capture branch of 287Fl leading to 287Nh and 283Rg.[14]

The now-confirmed discovery of flerovium was made in June 1999 when the Dubna team repeated the first reaction from 1998. This time, two atoms of flerovium were produced; they alpha decayed with a half-life of 2.6 s, different from the 1998 result.[26] This activity was initially assigned to 288Fl in error, due to the confusion regarding the previous observations that were assumed to come from 289Fl. Further work in December 2002 finally allowed a positive reassignment of the June 1999 atoms to 289Fl.[30]

In May 2009, the Joint Working Party (JWP) of IUPAC published a report on the discovery of copernicium in which they acknowledged the discovery of the isotope 283Cn.[31] This implied the discovery of flerovium, from the acknowledgement of the data for the synthesis of 287Fl and 291Lv, which decay to 283Cn. The discovery of the isotopes flerovium-286 and -287 was confirmed in January 2009 at Berkeley. This was followed by confirmation of flerovium-288 and -289 in July 2009 at the Gesellschaft für Schwerionenforschung (GSI) in Germany. In 2011, IUPAC evaluated the Dubna team experiments of 1999–2007. They found the early data inconclusive, but accepted the results of 2004–2007 as flerovium, and the element was officially recognized as having been discovered.[32]

While the method of chemical characterisation of a daughter was successful in the cases of flerovium and livermorium, and the simpler structure of even–even nuclei made the confirmation of oganesson (element 118) straightforward, there have been difficulties in establishing the congruence of decay chains from isotopes with odd protons, odd neutrons, or both.[33][34] To get around this problem with hot fusion, the decay chains from which terminate in spontaneous fission instead of connecting to known nuclei as cold fusion allows, experiments were performed at Dubna in 2015 to produce lighter isotopes of flerovium in the reactions of 48Ca with 239Pu and 240Pu, particularly 283Fl, 284Fl, and 285Fl; the last had previously been characterised in the 242Pu(48Ca,5n)285Fl reaction at the Lawrence Berkeley National Laboratory in 2010. The isotope 285Fl was more clearly characterised, while the new isotope 284Fl was found to undergo immediate spontaneous fission instead of alpha decay to known nuclides around the N = 162 shell closure, and 283Fl was not found.[12] This lightest isotope may yet conceivably be produced in the cold fusion reaction 208Pb(76Ge,n)283Fl,[15] which the team at RIKEN in Japan has considered investigating:[35][36] this reaction is expected to have a higher cross-section of 200 fb than the "world record" low of 30 fb for 209Bi(70Zn,n)278Nh, the reaction which RIKEN used for the official discovery of element 113, now named nihonium.[15][37][38] The Dubna team repeated their investigation of the 240Pu+48Ca reaction in 2017, observing three new consistent decay chains of 285Fl, an additional decay chain from this nuclide that may pass through some isomeric states in its daughters, a chain that could be assigned to 287Fl (likely stemming from 242Pu impurities in the target), and some spontaneous fission events of which some could be from 284Fl, though other interpretations including side reactions involving the evaporation of charged particles are also possible.[13]


Stamp of Russia, issued in 2013, dedicated to Georgy Flyorov and flerovium

Using Mendeleev's nomenclature for unnamed and undiscovered elements, flerovium is sometimes called eka-lead. In 1979, IUPAC published recommendations according to which the element was to be called ununquadium (with the corresponding symbol of Uuq),[39] a systematic element name as a placeholder, until the discovery of the element is confirmed and a permanent name is decided on. Most scientists in the field called it "element 114", with the symbol of E114, (114) or 114.[2]

According to IUPAC recommendations, the discoverer(s) of a new element has the right to suggest a name.[40] After the discovery of flerovium and livermorium was recognized by IUPAC on 1 June 2011, IUPAC asked the discovery team at the JINR to suggest permanent names for those two elements. The Dubna team chose to name element 114 flerovium (symbol Fl),[41][42] after the Russian Flerov Laboratory of Nuclear Reactions (FLNR), named after the Soviet physicist Georgy Flyorov (also spelled Flerov); earlier reports claim the element name was directly proposed to honour Flyorov.[43] In accordance with the proposal received from the discoverers IUPAC officially named flerovium after the Flerov Laboratory of Nuclear Reactions (an older name for the JINR), not after Flyorov himself.[10] Flyorov is known for writing to Joseph Stalin in April 1942 and pointing out the silence in scientific journals in the field of nuclear fission in the United States, Great Britain, and Germany. Flyorov deduced that this research must have become classified information in those countries. Flyorov's work and urgings led to the development of the USSR's own atomic bomb project.[42] Flyorov is also known for the discovery of spontaneous fission with Konstantin Petrzhak. The naming ceremony for flerovium and livermorium was held on 24 October 2012 in Moscow.[44]

Predicted properties

Nuclear stability and isotopes

IBA nuclear shells
Regions of differently shaped nuclei, as predicted by the Interacting Boson Approximation[23]

The physical basis of the chemical periodicity governing the periodic table is the electron shell closures at each noble gas (atomic numbers 2, 10, 18, 36, 54, 86, and 118): as any further electrons must enter a new shell with higher energy, closed-shell electron configurations are markedly more stable, leading to the relative inertness of the noble gases.[5] Since protons and neutrons are also known to arrange themselves in closed nuclear shells, the same effect happens at nucleon shell closures, which happen at specific nucleon numbers often dubbed "magic numbers". The known magic numbers are 2, 8, 20, 28, 50, and 82 for protons and neutrons, and additionally 126 for neutrons.[5] Nucleons with magic proton and neutron numbers, such as helium-4, oxygen-16, calcium-48, and lead-208, are termed "doubly magic" and are very stable against decay. This property of increased nuclear stability is very important for superheavy elements: without any stabilization, their half-lives would be expected by exponential extrapolation to be in the range of nanoseconds (10−9 s) when element 110 (darmstadtium) is reached, because of the ever-increasing repulsive electrostatic forces between the positively charged protons that overcome the limited-range strong nuclear force that holds the nucleus together. The next closed nucleon shells and hence magic numbers are thought to denote the centre of the long-sought island of stability, where the half-lives to alpha decay and spontaneous fission lengthen again.[5]

Next proton shell
Orbitals with high azimuthal 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. This raises the next proton shell to the region around element 120.[23]

Initially, by analogy with the neutron magic number 126, the next proton shell was also expected to occur at element 126, too far away from the synthesis capabilities of the mid-20th century to achieve much theoretical attention. In 1966, new values for the potential and spin-orbit interaction in this region of the periodic table[45] contradicted this and predicted that the next proton shell would occur instead at element 114,[5] and that nuclides in this region would be as stable against spontaneous fission as many heavy nuclei such as lead-208.[5] The expected closed neutron shells in this region were at neutron number 184 or 196, thus making 298Fl and 310Fl candidates for being doubly magic.[5] 1972 estimates predicted a half-life of about a year for 298Fl, which was expected to be near a large island of stability with the longest half-life at 294Ds (1010 years, comparable to that of 232Th).[5] After the synthesis of the first isotopes of elements 112 through 118 at the turn of the 21st century, it was found that the synthesized neutron-deficient isotopes were stabilized against fission. In 2008 it was thus hypothesized that the stabilization against fission of these nuclides was due to their being oblate nuclei, and that a region of oblate nuclei was centred on 288Fl. Additionally, new theoretical models showed that the expected gap in energy between the proton orbitals 2f7/2 (filled at element 114) and 2f5/2 (filled at element 120) was smaller than expected, so that element 114 no longer appeared to be a stable spherical closed nuclear shell. The next doubly magic nucleus is now expected to be around 306Ubb, but the expected low half-life and low production cross section of this nuclide makes its synthesis challenging.[23] Nevertheless, the island of stability is still expected to exist in this region of the periodic table, and nearer its centre (which has not been approached closely enough yet) some nuclides, such as 291Mc and its alpha- and beta-decay daughters,[a] may be found to decay by positron emission or electron capture and thus move into the centre of the island.[37] Due to the expected high fission barriers, any nucleus within this island of stability decays exclusively by alpha decay and perhaps some electron capture and beta decay,[5] both of which would bring the nuclei closer to the beta stability line where the island is expected to be. Electron capture is needed to reach the island, which is problematic because it is not certain that electron capture becomes a major decay mode in this region of the chart of nuclides.[37]

Several experiments have been performed between 2000 and 2004 at the Flerov Laboratory of Nuclear Reactions in Dubna studying the fission characteristics of the compound nucleus 292Fl by bombarding a plutonium-244 target with accelerated calcium-48 ions.[46] A compound nucleus is a loose combination of nucleons that have not yet arranged themselves into nuclear shells. It has no internal structure and is held together only by the collision forces between the target and projectile nuclei.[47][b] The results revealed how nuclei such as this fission predominantly by expelling doubly magic or nearly doubly magic fragments such as calcium-40, tin-132, lead-208, or bismuth-209. It was also found that the yield for the fusion-fission pathway was similar between calcium-48 and iron-58 projectiles, indicating a possible future use of iron-58 projectiles in superheavy element formation.[46] It has also been suggested that a neutron-rich flerovium isotope can be formed by the quasifission (partial fusion followed by fission) of a massive nucleus.[48] Recently it has been shown that the multi-nucleon transfer reactions in collisions of actinide nuclei (such as uranium and curium) might be used to synthesize the neutron-rich superheavy nuclei located at the island of stability,[48] although production of neutron-rich nobelium or seaborgium nuclei is more likely.[37]

Theoretical estimation of the alpha decay half-lives of the isotopes of the flerovium supports the experimental data.[49][50] The fission-survived isotope 298Fl, long expected to be doubly magic, is predicted to have alpha decay half-life around 17 days.[51][52] The direct synthesis of the nucleus 298Fl by a fusion–evaporation pathway is currently impossible since no known combination of target and stable projectile can provide 184 neutrons in the compound nucleus, and radioactive projectiles such as calcium-50 (half-life fourteen seconds) cannot yet be used in the needed quantity and intensity.[48] Currently, one possibility for the synthesis of the expected long-lived nuclei of copernicium (291Cn and 293Cn) and flerovium near the middle of the island include using even heavier targets such as curium-250, berkelium-249, californium-251, and einsteinium-254, that when fused with calcium-48 would produce nuclei such as 291Mc and 291Fl (as decay products of 299Uue, 295Ts, and 295Lv), with just enough neutrons to alpha decay to nuclides close enough to the centre of the island to possibly undergo electron capture and move inwards to the centre, though the cross sections would be small and little is yet known about the decay properties of superheavy nuclides near the beta stability line. This may be the best hope currently to synthesize nuclei on the island of stability, but it is speculative and may or may not work in practice.[37] Another possibility is to use controlled nuclear explosions to achieve the high neutron flux necessary to create macroscopic amounts of such isotopes.[37] This would mimic the r-process in which the actinides were first produced in nature and the gap of instability after polonium bypassed, as it would bypass the gaps of instability at 258–260Fm and at mass number 275 (atomic numbers 104 to 108).[37] Some such isotopes (especially 291Cn and 293Cn) may even have been synthesized in nature, but would have decayed away far too quickly (with half-lives of only thousands of years) and be produced in far too small quantities (about 10−12 the abundance of lead) to be detectable as primordial nuclides today outside cosmic rays.[37]

Atomic and physical

Flerovium is a member of group 14 in the periodic table, below carbon, silicon, germanium, tin, and lead. Every previous group 14 element has four electrons in its valence shell, forming a valence electron configuration of ns2np2. In flerovium's case, the trend will be continued and the valence electron configuration is predicted to be 7s27p2;[2] flerovium will behave similarly to its lighter congeners in many respects. Differences are likely to arise; a largely contributing effect is the spin–orbit (SO) interaction—the mutual interaction between the electrons' motion and spin. It is especially strong for the superheavy elements, because their electrons move faster than in lighter atoms, at velocities comparable to the speed of light.[53] In relation to flerovium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four.[54] The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to ​12 and ​32 for the more stabilized and less stabilized parts of the 7p subshell, respectively.[55][c] For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s2
.[2] These effects cause flerovium's chemistry to be somewhat different from that of its lighter neighbours.

Due to the spin-orbit splitting of the 7p subshell being very large in flerovium, and the fact that both flerovium's filled orbitals in the seventh shell are stabilized relativistically, the valence electron configuration of flerovium may be considered to have a completely filled shell, making flerovium a very noble metal. Its first ionization energy of 8.539 eV (823.9 kJ/mol) should be the highest in group 14.[2] The 6d electron levels are also destabilized, leading to some early speculations that they may be chemically active, although newer work suggests that this is unlikely.[5]

The closed-shell electron configuration of flerovium results in the metallic bonding in metallic flerovium being weaker than in the preceding and following elements; thus, flerovium is expected to have a low boiling point,[2] and has recently been suggested to be possibly a gaseous metal, similar to the predictions for copernicium, which also has a closed-shell electron configuration.[23] The melting and boiling points of flerovium were predicted in the 1970s to be around 70 °C and 150 °C,[2] significantly lower than the values for the lighter group 14 elements (those of lead are 327 °C and 1749 °C respectively), and continuing the trend of decreasing boiling points down the group. Although earlier studies predicted a boiling point of ~1000 °C or 2840 °C,[5] this is now considered unlikely because of the expected weak metallic bonding in flerovium and that group trends would expect flerovium to have a low sublimation enthalpy.[2] Recent experimental indications have suggested that the pseudo-closed shell configuration of flerovium results in very weak metallic bonding and hence that flerovium is probably a gas at room temperature with a boiling point of around −60 °C.[3] Like mercury, radon, and copernicium, but not lead and oganesson (eka-radon), flerovium is calculated to have no electron affinity.[56]

In the solid state, flerovium is expected to be a dense metal due to its high atomic weight, with a density variously predicted to be either 22 g/cm3 or 14 g/cm3.[2] Flerovium is expected to crystallize in the face-centred cubic crystal structure like that of its lighter congener lead,[9] although earlier calculations predicted a hexagonal close-packed crystal structure due to spin-orbit coupling effects.[57] The electron of the hydrogen-like flerovium ion (oxidized so that it only has one electron, Fl113+) is expected to move so fast that it has a mass 1.79 times that of a stationary electron, due to relativistic effects. For comparison, the figures for hydrogen-like lead and tin are expected to be 1.25 and 1.073 respectively.[58] Flerovium would form weaker metal–metal bonds than lead and would be adsorbed less on surfaces.[58]


Flerovium is the heaviest known member of group 14 in the periodic table, below lead, and is projected to be the second member of the 7p series of chemical elements. Nihonium and flerovium are expected to form a very short subperiod, coming between the filling of the 6d5/2 and 7p1/2 subshells. Their chemical behaviour is expected to be very distinctive: nihonium's homology to thallium has been called "doubtful" by computational chemists, while flerovium's to lead has been called only "formal".[59]

The first five members of group 14 show the group oxidation state of +4 and the latter members have an increasingly prominent +2 chemistry due to the onset of the inert pair effect. Tin represents the point at which the stability of the +2 and +4 states are similar, and lead(II) is the most stable of all the chemically well-understood group 14 elements in the +2 oxidation state.[2] The 7s orbitals are very highly stabilized in flerovium and thus a very large sp3 orbital hybridization is required to achieve the +4 oxidation state, so flerovium is expected to be even more stable than lead in its strongly predominant +2 oxidation state and its +4 oxidation state should be highly unstable.[2] For example, flerovium dioxide (FlO2) is expected to be highly unstable to decomposition into its constituent elements (and would not be formed from the direct reaction of flerovium with oxygen),[2][60] and flerovane (FlH4), which should have Fl–H bond lengths of 1.787 Å,[6] is predicted to be more thermodynamically unstable than plumbane, spontaneously decomposing into flerovium(II) hydride (FlH2) and hydrogen gas.[61] Flerovium tetrafluoride (FlF4)[62] would have bonding mostly due to sd hybridizations rather than sp3 hybridizations,[63] and its decomposition to the difluoride and fluorine gas would be exothermic.[6] The gross destabilization of all the tetrahalides (for example, FlCl4 is destabilized by about 400 kJ/mol) is unfortunate because otherwise these compounds would be very useful in gas-phase chemical studies of flerovium.[6] The corresponding polyfluoride anion FlF2−
should be unstable to hydrolysis in aqueous solution, and flerovium(II) polyhalide anions such as FlBr
and FlI
are predicted to form preferentially in flerovium-containing solutions.[2] The sd hybridizations were suggested in early calculations as the 7s and 6d electrons in flerovium share approximately the same energy, which would allow a volatile hexafluoride to form, but later calculations do not confirm this possibility.[5] In general, the spin-orbit contraction of the 7p1/2 orbital should lead to smaller bond lengths and larger bond angles: this has been theoretically confirmed in FlH2.[6] Nevertheless, even FlH2 should be relativistically destabilized by 2.6 eV to below Fl+H2; the large spin–orbit effects also break down the usual singlet–triplet divide in the group 14 dihydrides. FlF2 and FlCl2 are predicted to be more stable than FlH2.[64]

Due to the relativistic stabilization of flerovium's 7s27p2
valence electron configuration, the 0 oxidation state should also be more stable for flerovium than for lead, as the 7p1/2 electrons begin to also exhibit a mild inert pair effect:[2] this stabilization of the neutral state may bring about some similarities between the behaviour of flerovium and the noble gas radon.[18] Due to the expected relative inertness of flerovium, its diatomic compounds FlH and FlF should have lower energies of dissociation than the corresponding lead compounds PbH and PbF.[6] Flerovium(IV) should be even more electronegative than lead(IV);[62] lead(IV) has electronegativity 2.33 on the Pauling scale; the lead(II) value is only 1.87.

Flerovium(II) should be more stable than lead(II), and polyhalide ions and compounds of types FlX+, FlX2, FlX
, and FlX2−
(X = Cl, Br, I) are expected to form readily. The fluorides would undergo strong hydrolysis in aqueous solution.[2] All the flerovium dihalides are expected to be stable,[2] with the difluoride being water-soluble.[65] Spin-orbit effects would destabilize flerovium dihydride (FlH2) by almost 2.6 eV (250 kJ/mol).[60] In solution, flerovium would also form the oxoanion flerovite (FlO2−
) in aqueous solution, analogous to plumbite. Flerovium(II) sulfate (FlSO4) and sulfide (FlS) should be very insoluble in water, and flerovium(II) acetate (FlC2H3O2) and nitrate (Fl(NO3)2) should be quite water-soluble.[5] The standard electrode potential for the reduction of Fl2+ ions to metallic flerovium is estimated to be around +0.9 V, confirming the increased stability of flerovium in the neutral state.[2] In general, due to the relativistic stabilization of the 7p1/2 spinor, Fl2+ is expected to have properties intermediate between those of Hg2+ or Cd2+ and its lighter congener Pb2+.[2]

Experimental chemistry

Flerovium is currently the heaviest element to have had its chemistry experimentally investigated, although the chemical investigations have so far not led to a conclusive result. Two experiments were performed in April–May 2007 in a joint FLNR-PSI collaboration aiming to study the chemistry of copernicium. The first experiment involved the reaction 242Pu(48Ca,3n)287Fl and the second the reaction 244Pu(48Ca,4n)288Fl: these reactions produce short-lived flerovium isotopes whose copernicium daughters would then be studied.[66] The adsorption properties of the resultant atoms on a gold surface were compared with those of radon, as it was then expected that copernicium's full-shell electron configuration would lead to noble-gas like behaviour.[66] Noble gases interact with metal surfaces very weakly, which is uncharacteristic of metals.[66]

The first experiment allowed detection of three atoms of 283Cn but also seemingly detected 1 atom of 287Fl. This result was a surprise given the transport time of the product atoms is ~2 s, so the flerovium atoms produced should have decayed to copernicium before adsorption. In the second reaction, 2 atoms of 288Fl and possibly 1 atom of 289Fl were detected. Two of the three atoms displayed adsorption characteristics associated with a volatile, noble-gas-like element, which has been suggested but is not predicted by more recent calculations. These experiments provided independent confirmation for the discovery of copernicium, flerovium, and livermorium via comparison with published decay data. Further experiments in 2008 to confirm this important result detected a single atom of 289Fl, and supported previous data showing flerovium having a noble-gas-like interaction with gold.[66]

The experimental support for a noble-gas-like flerovium soon weakened. In 2009 and 2010, the FLNR-PSI collaboration synthesized further atoms of flerovium to follow up their 2007 and 2008 studies. In particular, the first three flerovium atoms synthesized in the 2010 study suggested again a noble-gas-like character, but the complete set taken together resulted in a more ambiguous interpretation, unusual for a metal in the carbon group but not fully like a noble gas in character.[67] In their paper, the scientists refrained from calling flerovium's chemical properties "close to those of noble gases", as had previously been done in the 2008 study.[67] Flerovium's volatility was again measured through interactions with a gold surface, and provided indications that the volatility of flerovium was comparable to that of mercury, astatine, and the simultaneously investigated copernicium, which had been shown in the study to be a very volatile noble metal, conforming to its being the heaviest group 12 element known.[67] Nevertheless, it was pointed out that this volatile behaviour was not expected for a usual group 14 metal.[67]

In even later experiments from 2012 at the GSI, the chemical properties of flerovium were found to be more metallic than noble-gas-like. Jens Volker Kratz and Christoph Düllmann specifically named copernicium and flerovium as belonging to a new category of "volatile metals"; Kratz even speculated that they might be gaseous at standard temperature and pressure.[23][68] These "volatile metals", as a category, were expected to fall between normal metals and noble gases in terms of adsorption properties.[23] Contrary to the 2009 and 2010 results, it was shown in the 2012 experiments that the interactions of flerovium and copernicium respectively with gold were about equal.[69] Further studies showed that flerovium was more reactive than copernicium, in contradiction to previous experiments and predictions.[23]

In a 2014 paper detailing the experimental results of the chemical characterisation of flerovium, the GSI group wrote: "[flerovium] is the least reactive element in the group, but still a metal."[70] Nevertheless, in a 2016 conference about the chemistry and physics of heavy and superheavy elements, Alexander Yakushev and Robert Eichler, two scientists who had been active at GSI and FLNR in determining the chemistry of flerovium, still urged caution based on the inconsistencies of the various experiments previously listed, noting that the question of whether flerovium was a metal or a noble gas was still open with the available evidence: one study suggested a weak noble-gas-like interaction between flerovium and gold, while the other suggested a stronger metallic interaction. The same year, new experiments aimed at probing the chemistry of copernicium and flerovium were conducted at GSI's TASCA facility, and the data from these experiments is currently being analysed. As such, unambiguous determination of the chemical characteristics of flerovium has yet to have been established,[71] although the experiments to date have allowed the first experimental estimation of flerovium's boiling point: around −60 °C, so that it is probably a gas at standard conditions.[3] The longer-lived flerovium isotope 289Fl has been considered of interest for future radiochemical studies.[72]

See also


  1. ^ Specifically, 291Mc, 291Fl, 291Nh, 287Nh, 287Cn, 287Rg, 283Rg, and 283Ds, which are expected to decay to the relatively longer-lived nuclei 279Mt, 283Mt, 287Ds, and 291Cn.[37]
  2. ^ It is estimated that it requires around 10−14 s for the nucleons to arrange themselves into nuclear shells, at which point the compound nucleus becomes a nuclide, and this number is used by IUPAC as the minimum half-life a claimed isotope must have to be recognized as a nuclide.[47]
  3. ^ The quantum number corresponds to the letter in the electron orbital name: 0 to s, 1 to p, 2 to d, etc. See azimuthal quantum number for more information.


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External links


Calcium-48 is a scarce isotope of calcium containing 20 protons and 28 neutrons. It makes up 0.187% of natural calcium by mole fraction. Although it is unusually neutron-rich for such a light nucleus, its beta decay is extremely hindered, and so the only radioactive decay pathway that it has been observed to undergo is the extremely rare process of double beta decay. Its half-life is about 6.4×1019 years, so for all practical purposes it can be treated as stable. One factor contributing to this unusual stability is that 20 and 28 are both magic numbers, making 48Ca a "doubly magic" nucleus.

Since 48Ca is both practically stable and neutron-rich, it is a valuable starting material for the production of new nuclei in particle accelerators, both by fragmentation and by fusion reactions with other nuclei, for example in the discoveries of the heaviest five elements on the periodic table, from flerovium to oganesson. Heavier nuclei generally require a greater fraction of neutrons for maximum stability, so neutron-rich starting materials are necessary.

48Ca is the lightest nucleus known to undergo double beta decay and the only one simple enough to be analyzed with the sd nuclear shell model. It also releases more energy (4.27 MeV) than any other double beta decay candidate. These properties make it an interesting probe of nuclear structure models and a promising candidate in the ongoing search for neutrinoless double beta decay.

Carbon group

The carbon group is a periodic table group consisting of carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb), and flerovium (Fl).

In modern IUPAC notation, it is called Group 14. In the field of semiconductor physics, it is still universally called Group IV. The group was once also known as the tetrels (from the Greek word tetra, which means four), stemming from the Roman numeral IV in the group names, or (not coincidentally) from the fact that these elements have four valence electrons (see below).


Copernicium is a synthetic chemical element with symbol Cn and atomic number 112. It is an extremely radioactive element, and can only be created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 29 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.

In the periodic table of the elements, copernicium is a d-block transactinide element and a group 12 element. During reactions with gold, it has been shown to be an extremely volatile metal, so much so that it is probably a gas at standard temperature and pressure.

Copernicium is calculated to have several properties that differ from its lighter homologues in group 12, zinc, cadmium and mercury; due to relativistic effects, it may even give up its 6d electrons instead of its 7s ones. Copernicium has also been calculated to possibly show the oxidation state +4, while mercury shows it in only one compound of disputed existence and zinc and cadmium do not show it at all. It has also been predicted to be more difficult to oxidize copernicium from its neutral state than the other group 12 elements.

Extended periodic table

An extended periodic table theorizes 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.

If further elements with higher atomic numbers than this are discovered, they will be placed in additional periods, laid out (as with the existing periods) to illustrate periodically recurring trends in the properties of the elements concerned. Any additional periods are expected to contain a larger number of elements than the seventh period, as they are calculated to have an additional so-called g-block, containing at least 18 elements with partially filled g-orbitals in each period.An eight-period table containing this block was suggested by Glenn T. Seaborg in 1969. The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Despite many searches, no elements in this region have been synthesized or discovered in nature.According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals, but spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number. While Seaborg's version of the extended period had the heavier elements following the pattern set by lighter elements, as it did not take into account relativistic effects, models that take relativistic effects into account do not. Pekka Pyykkö and Burkhard Fricke used computer modeling to calculate the positions of elements up to Z = 172, and found that several were displaced from the Madelung rule. As a result of uncertainty and variability in predictions of chemical and physical properties of elements beyond 120, there is currently no consensus on their placement in the extended periodic table.

Elements in this region are likely to be highly unstable with respect to radioactive decay and undergo alpha decay or spontaneous fission with extremely short half-lives, though element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. Other islands of stability beyond the known elements may also be possible, including one theorized around element 164, though the extent of stabilizing effects from closed nuclear shells is uncertain. It is not clear how many elements beyond the expected island of stability are physically possible, whether period 8 is complete, or if there is a period 9. The International Union of Pure and Applied Chemistry (IUPAC) defines an element to exist if its lifetime is longer than 10−14 seconds (0.01 picoseconds, or 10 femtoseconds), which is the time it takes for the nucleus to form an electron cloud.As early as 1940, it was noted that a simplistic interpretation of the relativistic Dirac equation runs into problems with electron orbitals at Z > 1/α ≈ 137, suggesting that neutral atoms cannot exist beyond element 137, and that a periodic table of elements based on electron orbitals therefore breaks down at this point. On the other hand, a more rigorous analysis calculates the analogous limit to be Z ≈ 173 where the 1s subshell dives into the Dirac sea, and that it is instead not neutral atoms that cannot exist beyond element 173, but bare nuclei, thus posing no obstacle to the further extension of the periodic system. Atoms beyond this critical atomic number are called supercritical atoms.

Georgy Flyorov

Georgy Nikolayevich Flyorov (Russian: Гео́ргий Никола́евич Флёров, IPA: [gʲɪˈorgʲɪj nʲɪkɐˈlajɪvʲɪtɕ ˈflʲɵrəf]; 2 March 1913 – 19 November 1990) was a Soviet nuclear physicist who is known for his discovery of spontaneous fission and his contribution towards the physics of thermal reactions. In addition, he is also known for his letter directed to Joseph Stalin, during the midst of World War II, to start the atomic bomb project in the Soviet Union.

In 2012, element 114 was named flerovium after the research laboratory at the Joint Institute for Nuclear Research bearing his name.

Island of stability

In nuclear physics, the island of stability is the prediction that a set of superheavy nuclides with magic numbers of protons and neutrons will temporarily reverse the trend of decreasing stability in elements heavier than uranium. Various predictions have been made regarding the exact location of the island of stability, though it is generally thought to center near copernicium and flerovium isotopes (such as 291Cn, 293Cn, and 298Fl) approaching the predicted closed shell at N = 184. It is thought that the closed shell will confer additional stability towards fission, while also leading to longer half-lives towards alpha decay. While these effects are expected to be greatest near Z = 114 and N = 184, the region of increased stability is expected to encompass several neighboring elements, and there may also be additional islands of stability around heavier doubly magic nuclei. Estimates of the stability of the elements on the island are usually around a half-life of minutes or days; however, some estimates predict half-lives of millions of years.Although the nuclear shell model predicting magic numbers has existed since the 1940s, the existence of long-lived superheavy nuclides has not been definitively demonstrated. Like the rest of the superheavy elements, the nuclides on the island of stability have never been found in nature; thus, they must be created artificially in a nuclear reaction to be studied. Scientists have not found a way to carry out such a reaction; it is likely that new types of reactions will be needed to populate nuclei near the center of the island. Nevertheless, the successful synthesis of superheavy elements up to oganesson in recent years demonstrates a slight stabilizing effect around elements 110–114 that may continue in unknown isotopes, supporting the existence of the island of stability.

Isotopes of copernicium

Copernicium (112Cn) 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 277Cn in 1996. There are 6 known radioisotopes (with one more unconfirmed); the longest-lived isotope is 285Cn with a half-life of 29 seconds.

Isotopes of flerovium

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 (or possibly 1998). 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.

Isotopes of roentgenium

Roentgenium (111Rg) 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 272Rg in 1994, which is also the only directly synthesized isotope; all others are decay products of nihonium, moscovium, and tennessine, and possibly copernicium, flerovium, and livermorium. There are 7 known radioisotopes from 272Rg to 282Rg. The longest-lived isotope is 282Rg with a half-life of 2.1 minutes, although the unconfirmed 283Rg and 286Rg may have a longer half-life of about 5.1 minutes and 10.7 minutes respectively.


Livermorium is a synthetic chemical element with 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. 4 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 the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 16 as the heaviest chalcogen, although it has not been confirmed to behave as the heavier homologue to the chalcogen polonium. Livermorium is calculated to have some similar properties to its lighter homologues (oxygen, sulfur, selenium, tellurium, and polonium), and be a post-transition metal, although it should also show several major differences from them.

Major actinide

Major actinides is a term used in the nuclear power industry that refers to the plutonium and uranium present in used nuclear fuel, as opposed to the minor actinides neptunium, americium, curium, berkelium, and californium.


Moscovium is a synthetic chemical element with 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.Moscovium is an extremely radioactive element: its most stable known isotope, moscovium-290, has a half-life of only 0.8 seconds. In the periodic table, it is a p-block transactinide element. It is a member of the 7th period and is placed in group 15 as the heaviest pnictogen, although it has not been confirmed to behave as a heavier homologue of the pnictogen bismuth. Moscovium is calculated to have some properties similar to its lighter homologues, nitrogen, phosphorus, arsenic, antimony, and bismuth, and to be a post-transition metal, although it should also show several major differences from them. In particular, moscovium should also have significant similarities to thallium, as both have one rather loosely bound electron outside a quasi-closed shell. About 100 atoms of moscovium have been observed to date, all of which have been shown to have mass numbers from 287 to 290.


Oganesson is a synthetic chemical element with symbol Og and atomic number 118. It was first synthesized in 2002 at the Joint Institute for Nuclear Research (JINR) in Dubna, near Moscow in Russia, by a joint team of Russian and American scientists. In December 2015, it was recognized as one of four new elements by the Joint Working Party of the international scientific bodies IUPAC and IUPAP. It was formally named on 28 November 2016. The name is in line with the tradition of honoring a scientist, in this case the nuclear physicist Yuri Oganessian, who has played a leading role in the discovery of the heaviest elements in the periodic table. It is one of only two elements named after a person who was alive at the time of naming, the other being seaborgium; it is also the only element whose namesake is alive today.Oganesson has the highest atomic number and highest atomic mass of all known elements. The radioactive oganesson atom is very unstable, and since 2005, only five (possibly six) atoms of the nuclide 294Og have been detected. Although this allowed very little experimental characterization of its properties and possible compounds, theoretical calculations have resulted in many predictions, including some surprising ones. For example, although oganesson is a member of group 18 – the first synthetic element to be so – it may be significantly reactive, unlike all the other elements of that group (the noble gases). It was formerly thought to be a gas under normal conditions but is now predicted to be a solid due to relativistic effects. On the periodic table of the elements it is a p-block element and the last one of the 7th period.

Periodic table (crystal structure)

For elements that are solid at standard temperature and pressure the table gives the crystalline structure of the most thermodynamically stable form(s) in those conditions. In all other cases the structure given is for the element at its melting point. Data is presented only for the first 114 elements as well as the 118th (hydrogen through flerovium and oganesson), and predictions are given for elements that have never been produced in bulk (astatine, francium, and elements 100–114 and 118).

Transactinide element

In chemistry, transactinide elements (also transactinides, superheavy elements, or super-heavy elements) are the chemical elements with atomic numbers from 104 to 120. Their atomic numbers are immediately greater than those of the actinides, the heaviest of which is lawrencium (atomic number 103).

Glenn T. Seaborg first proposed the actinide concept, which led to the acceptance of the actinide series. He also proposed the transactinide series ranging from element 104 to 121 and the superactinide series approximately spanning elements 122 to 153. The transactinide seaborgium was named in his honor.By definition, transactinide elements are also transuranic elements, i.e. have an atomic number greater than uranium (92).

The transactinide elements all have electrons in the 6d subshell in their ground state. Except for rutherfordium and dubnium, even the longest-lasting isotopes of transactinide elements have extremely short half-lives of minutes or less. The element naming controversy involved the first five or six transactinide elements. These elements thus used systematic names for many years after their discovery had been confirmed. (Usually the systematic names are replaced with permanent names proposed by the discoverers relatively shortly after a discovery has been confirmed.)

Transactinides are radioactive and have only been obtained synthetically in laboratories. None of these elements have ever been collected in a macroscopic sample. Transactinide elements are all named after physicists and chemists or important locations involved in the synthesis of the elements.

IUPAC defines an element to exist if its lifetime is longer than 10−14 seconds, which is the time it takes for the nucleus to form an electron cloud.

Transuranium 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.


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, 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.

Early interest in possible increased stability led to the first attempted synthesis of unbihexium in 1971 and searches for it in nature in subsequent years. Despite several reported observations, more recent studies suggest that these experiments were insufficiently sensitive; hence, no unbihexium has been found naturally or artificially. The stability of unbihexium is also widely debated, as the island of stability may in fact lie at a lower atomic number, closer to copernicium and flerovium.

Unbihexium is predicted to be a chemically active superactinide, exhibiting a variety of oxidation states from +1 to +8, and possibly be a heavier congener of plutonium. It is predicted to be the second element with an electron in a g orbital, a consequence of relativistic effects seen only in heavy and superheavy elements. An overlap in energy levels of the 5g, 6f, 7d, and 8p orbitals is also expected, which complicates predictions of chemical properties for this element.


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, until 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.

Unbinilium has not yet been synthesized, despite multiple attempts from German and Russian teams. One 2011 attempt from the German team at the GSI Helmholtz Centre for Heavy Ion Research had a suggestive but not conclusive result suggesting the possible production of 299Ubn, but the data was incomplete and did not match theoretical expectations. Planned attempts from Russian, Japanese, and French teams are scheduled for 2017–2020. Experimental evidence from these attempts shows that the period 8 elements would likely be far more difficult to synthesise than the previous known elements, and that unbinilium may even be the last element that can be synthesized with current technology.

Unbinilium's position as the seventh alkaline earth metal suggests that it would have similar properties to its lighter congeners, beryllium, magnesium, calcium, strontium, barium, and radium; however, relativistic effects may cause some of its properties to differ from those expected from a straight application of periodic trends. For example, unbinilium is expected to be less reactive than barium and radium and be closer in behavior to strontium, and while it should show the characteristic +2 oxidation state of the alkaline earth metals, it is also predicted to show the +4 oxidation state, which is unknown in any other alkaline earth metals.


Unbiunium, also known as eka-actinium or simply element 121, is the hypothetical chemical element with symbol Ubu and atomic number 121. Unbiunium and Ubu are the temporary systematic IUPAC name and symbol respectively, until a permanent name is decided upon. In the periodic table of the elements, it is expected to be the first of the superactinides, and the third element in the eighth period: analogously to lanthanum and actinium, it could be considered the fifth member of group 3 and the first member of the fifth-row transition metals. 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.

Unbiunium has not yet been synthesized. Nevertheless, because it is only three elements away from the heaviest known element, oganesson (element 118), its synthesis may come in the near future; it is expected to be one of the last few reachable elements with current technology, and the limit may be anywhere between element 120 and 124. It will also likely be far more difficult to synthesize than the elements known so far up to 118, and still more difficult than elements 119 and 120. The team at RIKEN in Japan has plans to attempt the synthesis of element 121 in the future after its attempts on elements 119 and 120.

The position of unbiunium in the periodic table suggests that it would have similar properties to its lighter congeners, scandium, yttrium, lanthanum, and actinium; however, relativistic effects may cause some of its properties to differ from those expected from a straight application of periodic trends. For example, unbiunium is expected to have a s2p valence electron configuration instead of the s2d of its lighter congeners in group 3, but this is not expected to significantly affect its chemistry, which is predicted to be that of a normal group 3 element; it would on the other hand significantly lower its first ionisation energy beyond what would be expected from periodic trends.

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