Rutherfordium

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Rutherfordium, 104Rf
Rutherfordium
Pronunciation /ˌrʌðərˈfɔːrdiəm/ ( Loudspeaker.svg listen )(RUDH-ər-FOR-dee-əm)
Mass number [267]
Rutherfordium 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
Hf

Rf

(Upo)
lawrenciumrutherfordiumdubnium
Atomic number (Z)104
Group group 4
Period period 7
Block d-block
Element category   Transition metal
Electron configuration [ Rn ] 5f14 6d2 7s2 [1] [2]
Electrons per shell
2, 8, 18, 32, 32, 10, 2
Physical properties
Phase at  STP solid (predicted) [1] [2]
Melting point 2400  K (2100 °C,3800 °F)(predicted) [1] [2]
Boiling point 5800 K(5500 °C,9900 °F)(predicted) [1] [2]
Density (near r.t.)23.2 g/cm3(predicted) [1] [2] [3]
Atomic properties
Oxidation states (+2), (+3), +4 [1] [2] [3] (parenthesized: prediction)
Ionization energies
  • 1st: 580 kJ/mol
  • 2nd: 1390 kJ/mol
  • 3rd: 2300 kJ/mol
  • (more)(all but first estimated) [2]
Atomic radius empirical:150  pm (estimated) [2]
Covalent radius 157 pm(estimated) [1]
Other properties
Natural occurrence synthetic
Crystal structure hexagonal close-packed (hcp)
Hexagonal close packed.svg

(predicted) [4]
CAS Number 53850-36-5
History
Namingafter Ernest Rutherford
Discovery Joint Institute for Nuclear Research and Lawrence Berkeley National Laboratory (1964, 1969)
Main isotopes of rutherfordium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
261Rf syn 70 s [5] >80% α 257No
<15% ε 261Lr
<10% SF
263Rfsyn15 min [5] <100% SF
~30% α 259No
265Rfsyn1.1 min [6] SF
266Rfsyn23 s?SF
267Rfsyn1.3 h [5] SF
| references

Rutherfordium is a synthetic chemical element with the symbol Rf and atomic number 104, named after New Zealand physicist Ernest Rutherford. As a synthetic element, it is not found in nature and can only be created in a laboratory. It is radioactive; the most stable known isotope, 267Rf, has a half-life of approximately 1.3 hours.

Contents

In the periodic table of the elements, it is a d-block element and the second of the fourth-row transition elements. It is a member of the 7th period and belongs to the group 4 elements. Chemistry experiments have confirmed that rutherfordium behaves as the heavier homologue to hafnium in group 4. The chemical properties of rutherfordium are characterized only partly. They compare well with the chemistry of the other group 4 elements, even though some calculations had indicated that the element might show significantly different properties due to relativistic effects.

In the 1960s, small amounts of rutherfordium were produced in the Joint Institute for Nuclear Research in the former Soviet Union and at Lawrence Berkeley National Laboratory in California. [7] The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and it was not until 1997 that International Union of Pure and Applied Chemistry (IUPAC) established rutherfordium as the official name for the element.

History

Discovery

Rutherfordium was reportedly first detected in 1964 at the Joint Institute of Nuclear Research at Dubna (then in the Soviet Union). Researchers there bombarded a plutonium-242 target with neon-22 ions and separated the reaction products by gradient thermochromatography after conversion to chlorides by interaction with ZrCl4. The team identified spontaneous fission activity contained within a volatile chloride portraying eka-hafnium properties. Although a half-life was not accurately determined, later calculations indicated that the product was most likely rutherfordium-259 (abbreviated as 259Rf in standard notation): [8]

242
94
Pu
+ 22
10
Ne
264−x
104
Rf
264−x
104
Rf
Cl4

In 1969, researchers at the University of California, Berkeley conclusively synthesized the element by bombarding a californium-249 target with carbon-12 ions and measured the alpha decay of 257Rf, correlated with the daughter decay of nobelium-253: [9]

249
98
Cf
+ 12
6
C
257
104
Rf
+ 4
n

The American synthesis was independently confirmed in 1973 and secured the identification of rutherfordium as the parent by the observation of K-alpha X-rays in the elemental signature of the 257Rf decay product, nobelium-253. [10]

Naming controversy

Element 104 was eventually named after Ernest Rutherford Ernest Rutherford2.jpg
Element 104 was eventually named after Ernest Rutherford

The Russian scientists proposed the name kurchatovium and the American scientists suggested the name rutherfordium for the new element. [11] In 1992, the IUPAC/IUPAP Transfermium Working Group (TWG) assessed the claims of discovery and concluded that both teams provided contemporaneous evidence to the synthesis of element 104 and that credit should be shared between the two groups. [8]

The American group wrote a scathing response to the findings of the TWG, stating that they had given too much emphasis on the results from the Dubna group. In particular they pointed out that the Russian group had altered the details of their claims several times over a period of 20 years, a fact that the Russian team does not deny. They also stressed that the TWG had given too much credence to the chemistry experiments performed by the Russians and accused the TWG of not having appropriately qualified personnel on the committee. The TWG responded by saying that this was not the case and having assessed each point raised by the American group said that they found no reason to alter their conclusion regarding priority of discovery. [12] The IUPAC finally used the name suggested by the American team (rutherfordium) which may in some way reflect a change of opinion. [13]

As a consequence of the initial competing claims of discovery, an element naming controversy arose. Since the Soviets claimed to have first detected the new element they suggested the name kurchatovium (Ku) in honor of Igor Kurchatov (1903–1960), former head of Soviet nuclear research. This name had been used in books of the Soviet Bloc as the official name of the element. The Americans, however, proposed rutherfordium (Rf) for the new element to honor Ernest Rutherford, who is known as the "father" of nuclear physics. The International Union of Pure and Applied Chemistry (IUPAC) adopted unnilquadium (Unq) as a temporary, systematic element name, derived from the Latin names for digits 1, 0, and 4. In 1994, IUPAC suggested the name dubnium (Db) to be used since rutherfordium was suggested for element 106 and IUPAC felt that the Dubna team should be recognized for their contributions. However, there was still a dispute over the names of elements 104–107. In 1997 the teams involved resolved the dispute and adopted the current name rutherfordium. The name dubnium was given to element 105 at the same time. [13]

Isotopes

Isotope half-lives and discovery years
Isotope
Half-life
[5]
Decay
mode [5]
Discovery
year
Reaction
253Rf48 μsα, SF1994204Pb(50Ti,n) [14]
254Rf23 μsSF1994206Pb(50Ti,2n) [14]
255Rf2.3 sε?, α, SF1974207Pb(50Ti,2n) [15]
256Rf6.4 msα, SF1974208Pb(50Ti,2n) [15]
257Rf4.7 sε, α, SF1969249Cf(12C,4n) [9]
257mRf4.1 sε, α, SF1969249Cf(12C,4n) [9]
258Rf14.7 msα, SF1969249Cf(13C,4n) [9]
259Rf3.2 sα, SF1969249Cf(13C,3n) [9]
259mRf2.5 sε1969249Cf(13C,3n) [9]
260Rf21 msα, SF1969248Cm(16O,4n) [8]
261Rf78 sα, SF1970248Cm(18O,5n) [16]
261mRf4 sε, α, SF2001244Pu(22Ne,5n) [17]
262Rf2.3 sα, SF1996244Pu(22Ne,4n) [18]
263Rf15 minα, SF1999263Db(
e
,
ν
e
) [19]
263mRf ?8 sα, SF1999263Db(
e
,
ν
e
) [19]
265Rf1.1 min [6] SF2010269Sg(—,α) [20]
266Rf23 s?SF2007?266Db(
e
,
ν
e
)? [21] [22]
267Rf1.3 hSF2004271Sg(—,α) [23]
268Rf1.4 s?SF2004?268Db(
e
,
ν
e
)? [22] [24]
270Rf20 ms? [25] SF2010?270Db(
e
,
ν
e
)? [26]

Rutherfordium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Sixteen different isotopes have been reported with atomic masses from 253 to 270 (with the exceptions of 264 and 269). Most of these decay predominantly through spontaneous fission pathways. [5] [27]

Stability and half-lives

Out of isotopes whose half-lives are known, the lighter isotopes usually have shorter half-lives; half-lives of under 50 μs for 253Rf and 254Rf were observed. 256Rf, 258Rf, 260Rf are more stable at around 10 ms, 255Rf, 257Rf, 259Rf, and 262Rf live between 1 and 5 seconds, and 261Rf, 265Rf, and 263Rf are more stable, at around 1.1, 1.5, and 10 minutes respectively. The heaviest isotopes are the most stable, with 267Rf having a measured half-life of about 1.3 hours. [5]

The lightest isotopes were synthesized by direct fusion between two lighter nuclei and as decay products. The heaviest isotope produced by direct fusion is 262Rf; heavier isotopes have only been observed as decay products of elements with larger atomic numbers, of which only 267Rf has been confirmed. The heavy isotopes 266Rf and 268Rf have also been observed as electron capture daughters of the dubnium isotopes 266Db and 268Db, but have short half-lives to spontaneous fission. It seems likely that the same is true of 270Rf, a likely daughter of 270Db. [26]

In 1999, American scientists at the University of California, Berkeley, announced that they had succeeded in synthesizing three atoms of 293Og. [28] These parent nuclei were reported to have successively emitted seven alpha particles to form 265Rf nuclei, but their claim was retracted in 2001. [29] This isotope was later discovered in 2010 as the final product in the decay chain of 285Fl. [6] [20]

Predicted properties

Chemical

Rutherfordium is the first transactinide element and the second member of the 6d series of transition metals. Calculations on its ionization potentials, atomic radius, as well as radii, orbital energies, and ground levels of its ionized states are similar to that of hafnium and very different from that of lead. Therefore, it was concluded that rutherfordium's basic properties will resemble those of other group 4 elements, below titanium, zirconium, and hafnium. [19] [30] Some of its properties were determined by gas-phase experiments and aqueous chemistry. The oxidation state +4 is the only stable state for the latter two elements and therefore rutherfordium should also exhibit a stable +4 state. [30] In addition, rutherfordium is also expected to be able to form a less stable +3 state. [2] The standard reduction potential of the Rf4+/Rf couple is predicted to be higher than −1.7 V. [3]

Initial predictions of the chemical properties of rutherfordium were based on calculations which indicated that the relativistic effects on the electron shell might be strong enough that the 7p orbitals would have a lower energy level than the 6d orbitals, giving it a valence electron configuration of 6d1 7s2 7p1 or even 7s2 7p2, therefore making the element behave more like lead than hafnium. With better calculation methods and experimental studies of the chemical properties of rutherfordium compounds it could be shown that this does not happen and that rutherfordium instead behaves like the rest of the group 4 elements. [2] [30] Later it was shown in ab initio calculations with the high level of accuracy [31] [32] [33] that the Rf atom has the ground state with the 6d2 7s2 valence configuration and the low-lying excited 6d1 7s2 7p1 state with the excitation energy of only 0.3÷0.5 eV.

In an analogous manner to zirconium and hafnium, rutherfordium is projected to form a very stable, refractory oxide, RfO2. It reacts with halogens to form tetrahalides, RfX4, which hydrolyze on contact with water to form oxyhalides RfOX2. The tetrahalides are volatile solids existing as monomeric tetrahedral molecules in the vapor phase. [30]

In the aqueous phase, the Rf4+ ion hydrolyzes less than titanium(IV) and to a similar extent as zirconium and hafnium, thus resulting in the RfO2+ ion. Treatment of the halides with halide ions promotes the formation of complex ions. The use of chloride and bromide ions produces the hexahalide complexes RfCl2−
6
and RfBr2−
6
. For the fluoride complexes, zirconium and hafnium tend to form hepta- and octa- complexes. Thus, for the larger rutherfordium ion, the complexes RfF2−
6
, RfF3−
7
and RfF4−
8
are possible. [30]

Physical and atomic

Rutherfordium is expected to be a solid under normal conditions and assume a hexagonal close-packed crystal structure (c/a = 1.61), similar to its lighter congener hafnium. [4] It should be a very heavy metal with a density of around 23.2 g/cm3; in comparison, the densest known element that has had its density measured, osmium, has a density of 22.61 g/cm3. This results from rutherfordium's high atomic weight, the lanthanide and actinide contractions, and relativistic effects, although production of enough rutherfordium to measure this quantity would be impractical, and the sample would quickly decay. The atomic radius for rutherfordium is expected to be around 150  pm. Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Rf+ and Rf2+ ions are predicted to give up 6d electrons instead of 7s electrons, which is the opposite of the behavior of its lighter homologues. [2] When under high pressure (variously calculated as 72 or ~50 GPa), rutherfordium is expected to transition to a body-centered cubic crystal structure; hafnium transforms to this structure at 71±1 GPa, but has an intermediate ω structure that it transforms to at 38±8 GPa that is lacking for rutherfordium. [34]

Experimental chemistry

Summary of compounds and complex ions
FormulaNames
RfCl4rutherfordium tetrachloride, rutherfordium(IV) chloride
RfBr4rutherfordium tetrabromide, rutherfordium(IV) bromide
RfOCl2rutherfordium oxychloride, rutherfordyl(IV) chloride,
rutherfordium(IV) dichloride oxide
[RfCl6]2−hexachlororutherfordate(IV)
[RfF6]2−hexafluororutherfordate(IV)
K2[RfCl6]potassium hexachlororutherfordate(IV)

Gas phase

The tetrahedral structure of the RfCl4 molecule RfCl4.png
The tetrahedral structure of the RfCl4 molecule

Early work on the study of the chemistry of rutherfordium focused on gas thermochromatography and measurement of relative deposition temperature adsorption curves. The initial work was carried out at Dubna in an attempt to reaffirm their discovery of the element. Recent work is more reliable regarding the identification of the parent rutherfordium radioisotopes. The isotope 261mRf has been used for these studies, [30] though the long-lived isotope 267Rf (produced in the decay chains of 291Lv, 287Fl, and 283Cn) may be advantageous for future experiments. [35] The experiments relied on the expectation that rutherfordium would begin the new 6d series of elements and should therefore form a volatile tetrachloride due to the tetrahedral nature of the molecule. [30] [36] [37] Rutherfordium(IV) chloride is more volatile than its lighter homologue hafnium(IV) chloride (HfCl4) because its bonds are more covalent. [2]

A series of experiments confirmed that rutherfordium behaves as a typical member of group 4, forming a tetravalent chloride (RfCl4) and bromide (RfBr4) as well as an oxychloride (RfOCl2). A decreased volatility was observed for RfCl
4
when potassium chloride is provided as the solid phase instead of gas, highly indicative of the formation of nonvolatile K
2
RfCl
6
mixed salt. [19] [30] [38]

Aqueous phase

Rutherfordium is expected to have the electron configuration [Rn]5f14 6d2 7s2 and therefore behave as the heavier homologue of hafnium in group 4 of the periodic table. It should therefore readily form a hydrated Rf4+ ion in strong acid solution and should readily form complexes in hydrochloric acid, hydrobromic or hydrofluoric acid solutions. [30]

The most conclusive aqueous chemistry studies of rutherfordium have been performed by the Japanese team at Japan Atomic Energy Research Institute using the isotope 261mRf. Extraction experiments from hydrochloric acid solutions using isotopes of rutherfordium, hafnium, zirconium, as well as the pseudo-group 4 element thorium have proved a non-actinide behavior for rutherfordium. A comparison with its lighter homologues placed rutherfordium firmly in group 4 and indicated the formation of a hexachlororutherfordate complex in chloride solutions, in a manner similar to hafnium and zirconium. [30] [39]

261m
Rf4+
+ 6 Cl
[261mRfCl
6
]2−

Very similar results were observed in hydrofluoric acid solutions. Differences in the extraction curves were interpreted as a weaker affinity for fluoride ion and the formation of the hexafluororutherfordate ion, whereas hafnium and zirconium ions complex seven or eight fluoride ions at the concentrations used: [30]

261m
Rf4+
+ 6 F
[261mRfF
6
]2−

See also

Related Research Articles

Bohrium Chemical element with atomic number 107

Bohrium is a synthetic chemical element with the symbol Bh and atomic number 107. It is named after Danish physicist Niels Bohr. As a synthetic element, it can be created in a laboratory but is not found in nature. All known isotopes of bohrium are extremely radioactive; the most stable known isotope is 270Bh with a half-life of approximately 61 seconds, though the unconfirmed 278Bh may have a longer half-life of about 690 seconds.

Dubnium Chemical element with atomic number 105

Dubnium is a synthetic chemical element with the symbol Db and atomic number 105. Dubnium is highly radioactive: the most stable known isotope, dubnium-268, has a half-life of about 28 hours. This greatly limits the extent of research on dubnium.

Hafnium Chemical element with atomic number 72

Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1923, by Coster and Hevesy, making it the last stable element to be discovered. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.

Hassium Chemical element with atomic number 108

Hassium is a chemical element with the symbol Hs and the atomic number 108. It is not known to occur in nature and has been made only in laboratories in minuscule quantities. Hassium is highly radioactive; the most stable known isotope, 269Hs, has a half-life of approximately 16 seconds.

Lawrencium Chemical element with atomic number 103

Lawrencium is a synthetic chemical element with the symbol Lr and atomic number 103. It is named in honor of Ernest Lawrence, inventor of the cyclotron, a device that was used to discover many artificial radioactive elements. A radioactive metal, lawrencium is the eleventh transuranic element and is also the final member of the actinide series. Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles. Twelve isotopes of lawrencium are currently known; the most stable is 266Lr with a half-life of 11 hours, but the shorter-lived 260Lr is most commonly used in chemistry because it can be produced on a larger scale.

Meitnerium Chemical element with atomic number 109

Meitnerium is a synthetic chemical element with the symbol Mt and atomic number 109. It is an extremely radioactive synthetic element. The most stable known isotope, meitnerium-278, has a half-life of 4.5 seconds, although the unconfirmed meitnerium-282 may have a longer half-life of 67 seconds. The GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany, first created this element in 1982. It is named after Lise Meitner.

Seaborgium Chemical element with atomic number 106

Seaborgium is a synthetic chemical element with the symbol Sg and atomic number 106. It is named after the American nuclear chemist Glenn T. Seaborg. As a synthetic element, it can be created in a laboratory but is not found in nature. It is also radioactive; the most stable known isotope, 269Sg, has a half-life of approximately 14 minutes.

Darmstadtium Chemical element with atomic number 110

Darmstadtium is a synthetic chemical element with the symbol Ds and atomic number 110. It is an extremely radioactive synthetic element. The most stable known isotope, darmstadtium-281, has a half-life of approximately 12.7 seconds. Darmstadtium was first created in 1994 by the GSI Helmholtz Centre for Heavy Ion Research near the city of Darmstadt, Germany, after which it was named.

Oganesson Chemical element with atomic number 118

Oganesson is a synthetic chemical element with the 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, and the only element whose namesake is alive today.

Moscovium is a synthetic chemical element with the symbol Mc and atomic number 115. It was first synthesized in 2003 by a joint team of Russian and American scientists at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. In December 2015, it was recognized as one of four new elements by the Joint Working Party of international scientific bodies IUPAC and IUPAP. On 28 November 2016, it was officially named after the Moscow Oblast, in which the JINR is situated.

Copernicium Chemical element with atomic number 112

Copernicium is a synthetic chemical element with the symbol Cn and atomic number 112. Its known isotopes are extremely radioactive, and have only been created in a laboratory. The most stable known isotope, copernicium-285, has a half-life of approximately 28 seconds. Copernicium was first created in 1996 by the GSI Helmholtz Centre for Heavy Ion Research near Darmstadt, Germany. It is named after the astronomer Nicolaus Copernicus.

Flerovium Chemical element with atomic number 114

Flerovium is a superheavy artificial chemical element with the symbol Fl and atomic number 114. It is an extremely radioactive synthetic element. The element is named after the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna, Russia, where the element was discovered in 1998. The name of the laboratory, in turn, honours the Russian physicist Georgy Flyorov. The name was adopted by IUPAC on 30 May 2012.

Group 4 element group of chemical elements

Group 4 is a group of elements in the periodic table. It contains the elements titanium (Ti), zirconium (Zr), hafnium (Hf) and rutherfordium (Rf). This group lies in the d-block of the periodic table. The group itself has not acquired a trivial name; it belongs to the broader grouping of the transition metals.

Rutherfordium (104Rf) is a synthetic element and thus has no stable isotopes. A standard atomic weight cannot be given. The first isotope to be synthesized was either 259Rf in 1966 or 257Rf in 1969. There are 16 known radioisotopes from 253Rf to 270Rf and 4 isomers. The longest-lived isotope is 267Rf with a half-life of 2.5 hours, and the longest-lived isomer is 261mRf with a half-life of 81 seconds.

Dubnium (105Db) is a synthetic element, thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 261Db in 1968. The 13 known radioisotopes are from 255Db to 270Db, and 1–3 isomers. The longest-lived known isotope is 268Db with a half-life of 29 hours.

Seaborgium (106Sg) is a synthetic element and so has no stable isotopes. A standard atomic weight cannot be given. The first isotope to be synthesized was 263mSg in 1974. There are 12 known radioisotopes from 258Sg to 271Sg and 2 known isomers. The longest-lived isotope is 269Sg with a half-life of 14 minutes.

Hassium (108Hs) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 265Hs in 1984. There are 12 known isotopes from 263Hs to 277Hs and 1–4 isomers. The longest-lived isotope is 269Hs with a half-life of 16 seconds.

Nihonium (113Nh) is a synthetic element. Being synthetic, a standard atomic weight cannot be given and like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 284Nh as a decay product of 288Mc in 2003. The first isotope to be directly synthesized was 278Nh in 2004. There are 6 known radioisotopes from 278Nh to 286Nh, along with the unconfirmed 287Nh and 290Nh. The longest-lived isotope is 286Nh with a half-life of 8 seconds.

Flerovium (114Fl) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was 289Fl in 1999. Flerovium has seven known isotopes, and possibly 2 nuclear isomers. The longest-lived isotope is 289Fl with a half-life of 1.9 seconds, but the unconfirmed 290Fl may have a longer half-life of 19 seconds.

Tennessine (117Ts) is the most-recently synthesized synthetic element, and much of the data is hypothetical. As for any synthetic element, a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotopes to be synthesized were 293Ts and 294Ts in 2009. The longer-lived isotope is 294Ts with a half-life of 51 ms.

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