Definitions

flerovium

Nobelium

[noh-bel-ee-uhm, -bee-lee-]
Nobelium (or /noʊˈbiːliəm/) is a synthetic element with the symbol No and atomic number 102. It was first correctly identified in 1956 by scientists at the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. Little is known about the element but limited chemical experiments have shown that it forms a stable divalent ion in solution as well as the predicted trivalent ion that is associated with its presence as one of the actinoids.

Discovery profile

The discovery of element 102 was first announced by physicists at the Nobel Institute in Sweden in 1957. The team reported that they created an isotope with a half-life of 10 minutes, decaying by emission of an 8.5 MeV alpha particle, after bombarding 244Cm with 13C nuclei. The activity was assigned to 251102 or 253102. The scientists proposed the name nobelium (No) for the new element. Later they retracted their claim and associated the activity to background effects.

The synthesis of element 102 was then claimed in April 1958 at the University of California, Berkeley by Albert Ghiorso, Glenn T. Seaborg, John R. Walton and Torbjørn Sikkeland. The team used the new heavy-ion linear accelerator (HILAC) to bombard a curium target (95% 244Cm and 5% 246Cm) with 13C and 12C ions. They were unable to confirm the 8.5 MeV activity claimed by the Swedes but were instead able to detect decays from 250Fm, supposedly the daughter of 254102, which had an apparent half-life of ~3 s. In 1959 the team continued their studies and claimed that they were able to produce an isotope that decayed predominantly by emission of an 8.3 MeV alpha particle, with a half-life of 3 s with an associated 30% spontaneous fission branch. The activity was initially assigned to 254No but later changed to 252No. The Berkeley team decided to adopt the name nobelium for the element.

, ^{244}_{96}mathrm{Cm} + , ^{12}_{6}mathrm{C} to , ^{256}_{102}mathrm{No}^{*}to ,^{252}_{102}mathrm{No} + 4 ,^{1}_{0}mathrm{n}

Further work in 1961 on the attempted synthesis of element 103 (see lawrencium) produced evidence for a Z=102 alpha activity decaying by emission of an 8.2 MeV particle with a half-life of 15 s, and assigned to 255No.

Following initial work between 1958-1964, in 1966, a team at the Flerov Laboratory of Nuclear Reactions (FLNR) reported that they had been able to detect 250Fm from the decay of a parent nucleus (254No) with a half-life of ~50s, in contradiction to the Berkeley claim. Furthermore, they were able to show that the parent decayed by emission of 8.1 MeV alpha particles with a half-life of ~35 s.

, ^{238}_{92}mathrm{U} + , ^{22}_{10}mathrm{Ne} to , ^{260}_{102}mathrm{No}^{*}to ,^{254}_{102}mathrm{No} + 6 ,^{1}_{0}mathrm{n}

In 1969, the Dubna team carried out chemical experiments on element 102 and concluded that it behaved as the heavier homologue of Ytterbium. The Russian scientists proposed the name joliotium (Jo) for the new element.

Later work in 1967 at Berkeley and 1971 at Oak Ridge fully confirmed the discovery of element 102 and clarified earlier observations.

In 1992, the IUPAC-IUPAP Transfermium Working Group (TWG) assessed the claims of discovery and concluded that only the Dubna work from 1966 correctly detected and assigned decays to Z=102 nuclei at the time. The Dubna team are therefore officially recognised as the discoverers of nobelium although it is possible that it was detected at Berkeley in 1959.

Naming

Element 102 was first named nobelium (No) by its claimed discoverers in 1957 by scientists at the Nobel Institute in Sweden. The name was later adopted by Berkeley scientists who claimed its discovery in 1959.

The International Union of Pure and Applied Chemistry (IUPAC) officially recognised the name nobelium following the Berkeley results.

In 1969, Russian scientists working in Dubna disputed the claims of these groups and suggested the name joliotium (Jo), in recognition of the work of Frédéric Joliot-Curie.

In 1992, the TWG recognised the Dubna scientists as the official discoverers and acknowledged that the adoption of nobelium as the official name had been made prematurely.

Subsequently, there are indications that the IUPAC suggested the name flerovium (Fl) for the element in recognition of the Dubna laboratory and the name has been used in the literature in reference to the element.

However, in 1994, and subsequently in 1997, the IUPAC ratified the name nobelium (No) for the element on the basis that it had become entrenched in the literature over the course of 30 years and that Alfred Nobel should be commemorated in this fashion.

Contrary to some suggestions, at no time has element 102 been referred to as unnilbium due to the above circumstances.

Electronic structure

Nobelium is element 102 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 8, 2

Quantum mechanical model: 1s22s22p63s23p64s23d10 4p65s24d105p66s24f145d10 6p67s25f14

Physical properties

The appearance of this element is unknown, however it is most likely silvery-white or gray and metallic. If sufficient amounts of nobelium were produced, it would pose a radiation hazard. Some sources quote a melting point of 827oC for nobelium but this cannot be substantiated from an official source and seems implausible regarding the requirements of such a measurement. However, the 1st, 2nd and 3rd ionization energies have been measured. In addition, an electronegativity value of 1.3 is also sometimes quoted. This is most definitely only an estimate since a true value can only be determined using a chemical compound of the element and no such compounds exist for nobelium.

Experimental chemistry

Aqueous phase chemistry

First experiments involving nobelium assumed that it predominantly formed a +III state like earlier actinoids. However, it was later found that nobelium forms a stable +II state in solution, although it can be oxidised to an oxidising +III state. A reduction potential of -1.78 V has been measured for the No3+ ion. The hexaaquanobelium(II) ion has been determined to have an ionic radius of 110 pm.

Summary of compounds and (complex) ions

Formula Names(s)
[No(H2O)6]3+ hexaaquanobelium(III)
[No(H2O)6]2+ hexaaquanobelium(II)

Isotopes

Seventeen radioisotopes of nobelium have been characterized, with the most stable being 259No with a half-life of 58 minutes. Longer half-lives are expected for the as-yet-unknown 261No and 263No. An isomeric level has been found in 253No and K-isomers have been found in 250No, 252No and 254No to date.

Synthesis of isotopes as decay products

Isotopes of nobelium have also been identified in the decay of heavier elements. Observations to date are summarised in the table below:

Evaporation Residue Observed No isotope
262Lr 262No
269Hs, 265Sg, 261Rf 257No
267Hs, 263Sg, 259Rf 255No
254Lr 254No
261Sg, 257Rf 253No
264Hs, 260Sg, 256Rf 252No
255Rf 251No

Chronology of isotope discovery

Isotope Year discovered Discovery reaction
250Nom 2001 204Pb(48Ca,2n)
250Nog 2006 204Pb(48Ca,2n)
251No 1967 244Cm(12C,5n)
252Nog 1959 244Cm(12C,4n)
252Nom ~2002 206Pb(48Ca,2n)
253Nog 1967 242Pu(16O,5n),239Pu(18O,4n)
253Nom 1971 249Cf(12C,4n)
254Nog 1966 243Am(15N,4n)
254Nom1 1967? 246Cm(13C,5n),246Cm(12C,4n)
254Nom2 ~2003 208Pb(48Ca,2n)
255No 1967 246Cm(13C,4n),248Cm(12C,5n)
256No 1967 248Cm(12C,4n),248Cm(13C,5n)
257No 1961? , 1967 248Cm(13C,4n)
258No 1967 248Cm(13C,3n)
259No 1973 248Cm(18O,α3n)
260No ? 254Es + 22Ne,18O,13C - transfer
261No unknown
262No 1988 254Es + 22Ne - transfer (EC of 262Lr)

Isomerism in nobelium nuclides

254No The study of K-isomerism was recently studied by physicists at the University of Jyvalkyla (JYFL). They were able to confirm a previously reported K-isomer and detected a second K-isomer. They assigned spins and parities of 8- and 16+ to the two K-isomers.

253No In 1971, Bemis et al. was able to determine an isomeric level decaying with a half-life of 31 µs from the decay of 257Rf. This was confirmed in 2003 at the GSI by also studying the decay of 257Rf. Further support in the same year from the FLNR appeared with a slightly higher half-life of 43.5 µs, decaying by M2 gamma emission to the ground state.

252No In a recent study by the GSI into K-isomerism in even-even isotopes, a K-isomer with a half-life of 110 ms was detected for 252No. A spin and parity of 8- was assigned to the isomer.

250No In 2003, scientists at the FLNR reported that they had been able to synthesise 249No which decayed by SF with a half-life of 54µs. Further work in 2006 by scientists at the ANL showed that the activity was actually due to a K-isomer in 250No. The ground state isomer was also detected with a very short half-life of 3.7µs.

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing nobelium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile Target CN 1n 2n 3n 4n
48Ca 208Pb 256No 254No: 2050 nb ; 22.3 MeV
48Ca 207Pb 255No 253No: 1310 nb ; 22.4 MeV
48Ca 206Pb 254No 253No: 58 nb ; 23.6 MeV 252No: 515 nb ; 23.3 MeV 251No: 30 nb ; 30.7 MeV 250No: 260 pb ; 43.9 MeV
48Ca 204Pb 252No 250No:13.2 nb ; 23.2 MeV

Hot fusion

The table below provides cross-sections and excitation energies for hot fusion reactions producing nobelium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Projectile Target CN 3n 4n 5n 6n
26Mg 232Th 258No 254No:1.6 nb 253No:9 nb 252No:8 nb
22Ne 238U 260No 256No:40 nb 255No:200 nb 254No:15 nb
22Ne 236U 258No 254No:7 nb 253No:25 nb 252No:15 nb

Retracted isotopes

In 2003, scientists at the FLNR claimed to have discovered the lightest known isotope of nobelium. However, subsequent work showed that the 54 µs activity was actually due to 250No and the isotope 249No was retracted.

References

Notes

External links

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