Nobelium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

102 mendelevium ← nobelium → lawrencium Yb ↑ No ↓ (Upb) Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	nobelium, No, 102
Chemical series	actinides
Group, Period, Block	n/a, 7, f
Appearance	unknown, probably silvery white or metallic gray
Standard atomic weight	[259]  g·mol−1
Electron configuration	[Rn] 5f14 7s2
Electrons per shell	2, 8, 18, 32, 32, 8, 2
Physical properties
Phase	solid
Atomic properties
Oxidation states	2, 3
Electronegativity	(Pauling scale)
Ionization energies	1st: 641.6 kJ/mol
	2nd: 1254.3 kJ/mol
	3rd: 2605.1 kJ/mol
Miscellaneous
CAS registry number	10028-14-5
Selected isotopes
Main article: Isotopes of nobelium iso NA half-life DM DE ( MeV) DP 262No syn 5 ms SF 260No syn 106 ms SF 259No syn 58m 75% α 7.69,7.61,7.53.... 255Fm 25% ε 259Md 258No syn 1.2 ms SF 257No syn 25 s α 8.32,8.22 253Fm 256No syn 2.91 s 99.5% α 8.45,8.40 252Fm 0.5% f 255No syn 3.1 m 61% α 8.12,8.08,7.93 251Fm 39% ε 2.012 255Md 254Nom2 syn 198 µs γ 254Nom1 254Nom1 syn 275 ms γ 250Nog 254Nog syn 51 s 253Nom syn 43.5 µs γ 253Nog 253No syn 1.62 m α 8.14,8.06,8.04,8.01 249Fm 252Nom syn 110 ms 252Nog syn 2.44 s 75% α 8.42,8.37 248Fm 25% SF 251No syn 0.76 s α 8.62,8.58 247Fm 250Nom syn 43 µs SF 250Nog syn 3.7 µs SF
References

Nobelium (pronounced /noʊˈbɛliəm/ or /noʊˈbiːliəm/) is a synthetic element with the symbol No and atomic number 102.

It was first correctly identified in 1966 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.

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.

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 (/juːˈnɪlbiəm/, symbol Unb) 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 1^st, 2^nd and 3^rd 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.

History of synthesis of isotopes by cold fusion

²⁰⁸Pb(⁴⁸Ca,xn)^256-xNo (x=1,2,3,4)

This cold fusion reaction was first studied in 1979 at the FLNR. Further work in 1988 at the GSI measured EC and SF branchings in ²⁵⁴No. In 1989, the FLNR used the reaction to measure SF decay characteristics for the two isomers of ²⁵⁴No. The measurement of the 2n excitation function was reported in 2001 by Yuri Oganessian at the FLNR.

Patin et al. at the LBNL reported in 2002 the synthesis of ^255-251No in the 1-4n exit channels and measured further decay data for these isotopes.

The reaction has recently been used at the Jyvaskylan Yliopisto Fysiikan Laitos (JYFL) using the RITU set-up to study K-isomerism in ²⁵⁴No. The scientists were able to measure two K-isomers with half-lives of 275 ms and 198 µs, respectively. They were assigned to 8^- and 16⁺ K-isomeric levels.

The reaction was used in 2004-5 at the FLNR to study the spectroscopy of ^255-253No. The team were able to confirm an isomeric level in ²⁵³No with a half-life of 43.5 µs.

²⁰⁸Pb(⁴⁴Ca,xn)^252-xNo (x=2)

This reaction was studied in 2003 at the FLNR in a study of the spectroscopy of ²⁵⁰No.

²⁰⁷Pb(⁴⁸Ca,xn)^255-xNo (x=2)

The measurement of the 2n excitation function for this reaction was reported in 2001 by Yuri Oganessian and co-workers at the FLNR. The reaction was used in 2004-5 to study the spectroscopy of ²⁵³No.

²⁰⁶Pb(⁴⁸Ca,xn)^254-xNo (x=1,2,3,4)

The measurement of the 1-4n excitation functions for this reaction were reported in 2001 by Yuri Oganessian and co-workers at the FLNR. The 2n channel was further studied by the GSI to provide a spectroscopic determination of K-isomerism in ²⁵²No. A K-isomer with spin and parity 8^- was detected with a half-life of 110 ms.

²⁰⁴Pb(⁴⁸Ca,xn)^252-xNo (x=2)

The measurement of the 2n excitation function for this reaction was reported in 2001 by Yuri Oganessian at the FLNR. They reported a new isotope ²⁵⁰No with a half-life of 36µs. The reaction was used in 2003 to study the spectroscopy of ²⁵⁰No.They were able to observe two spontaneous fission activities with half-lives of 5.6µs and 54µs and assigned to ²⁵⁰No and ²⁴⁹No, respectively. The latter activity was later assigned to a K-isomer in ²⁵⁰No. The reaction was reported in 2006 by Peterson et al. at the Argonne National Laboratory (ANL) in a study of SF in ²⁵⁰No. They detected two activities with half-lives of 3.7µs and 43µs and both assigned to ²⁵⁰No, the latter associated with a K-isomer.

History of synthesis of isotopes by hot fusion

²³²Th(²⁶Mg,xn)^258-xNo (x=4,5,6)

The cross sections for the 4-6n exit channels have been measured for this reaction at the FLNR.

²³⁸U(²²Ne,xn)^260-xNo (x=4,5,6)

This reaction was first studied in 1964 at the FLNR. The team were able to detect decays from ²⁵²Fm and ²⁵⁰Fm. The ²⁵²Fm activity was associated with an ~8 s half-life and assigned to ²⁵⁶102 from the 4n channel, with a yield of 45 nb. They were also able to detect a 10 s spontaneous fission activity also tentatively assigned to ²⁵⁶102. Further work in 1966 on the reaction examined the detection of ²⁵⁰Fm decay using chemical separation and a parent activity with a half-life of ~50 s was reported and correctly assigned to ²⁵⁴102. They also detected a 10 s spontaneous fission activity tentatively assigned to ²⁵⁶102. The reaction was used in 1969 to study some initial chemistry of nobelium at the FLNR. They determined eka-ytterbium properties, consistent with nobelium as the heavier homologue. In 1970, they were able to study the SF properties of ²⁵⁶No. In 2002, Patin et al. reported the synthesis of ²⁵⁶No from the 4n channel but were unable to detect ²⁵⁷No.

The cross section values for the 4-6n channels have also been studied at the FLNR.

²³⁸U(²⁰Ne,xn)^258-xNo

This reaction was studied in 1964 at the FLNR. No spontaneous fission activities were observed.

²³⁶U(²²Ne,xn)^258-xNo (x=4,5,6)

The cross sections for the 4-6n exit channels have been measured for this reaction at the FLNR.

²³⁵U(²²Ne,xn)^257-xNo (x=5)

This reaction was studied in 1970 at the FLNR. It was used to study the SF decay properties of ²⁵²No.

²³³U(²²Ne,xn)^255-xNo

The synthesis of neutron deficient nobelium isotopes was studied in 1975 at the FLNR. In their experiments they observed a 250 µs SF activity which they tentatively assigned to ²⁵⁰No in the 5n exit channel. Later results have not been able to confirm this activity and it is currently unidentified.

²⁴²Pu(¹⁸O,xn)^260-xNo (x=4?)

This reaction was studied in 1966 at the FLNR. The team identified an 8.2 s SF activity tentatively assigned to ²⁵⁶102.

²⁴¹Pu(¹⁶O,xn)^257-xNo

This reaction was first studied in 1958 at the FLNR. The team measured ~8.8 MeV alpha particles with a half-life of 30 s and assigned to ^253,252,251102. A repeat in 1960 produced 8.9 MeV alpha particles with a half-life of 2-40 s and assigned to ²⁵³102 from the 4n channel. Confidence in these results was later diminished.

²³⁹Pu(¹⁸O,xn)^257-xNo (x=5)

This reaction was studied in 1970 at the FLNR in an effort to study the SF decay properties of ²⁵²No.

²³⁹Pu(¹⁶O,xn)^255-xNo

This reaction was first studied in 1958 at the FLNR. The team were able to measure ~8.8 MeV alpha particles with a half-life of 30 s and assigned to ^253,252,251102. A repeat in 1960 was unsuccessful and it was concluded the first results were probably associated with background effects.

²⁴³Am(¹⁵N,xn)^258-xNo (x=4)

This reaction was studied in 1966 at the FLNR. The team were able to detect ²⁵⁰Fm using chemical techniques and determined an associated half-life significantly higher than the reported 3 s by Berkeley for the supposed parent ²⁵⁴No. Further work later the same year measured 8.1 MeV alpha particles with a half-life of 30-40 s.

²⁴³Am(¹⁴N,xn)^257-xNo

This reaction was studied in 1966 at the FLNR. They were unable to detect the 8.1 MeV alpha particles detected when using a N-15 beam.

²⁴¹Am(¹⁵N,xn)^256-xNo (x=4)

The decay properties of ²⁵²No were examined in 1977 at Oak Ridge. The team calculated a half-life of 2.3 s and measured a 27% SF branching.

²⁴⁸Cm(¹⁸O,αxn)^262-xNo (x=3)

The synthesis of the new isotope ²⁵⁹No was reported in 1973 from the LBNL using this reaction.

²⁴⁸Cm(¹³C,xn)^261-xNo (x=3?,4,5)

This reaction was first studied in 1967 at the LBNL. The new isotopes ²⁵⁸No,²⁵⁷No and ²⁵⁶No were detected in the 3-5n channels. The reaction was repeated in 1970 to provide further decay data for ²⁵⁷No.

²⁴⁸Cm(¹²C,xn)^260-xNo (4,5?)

This reaction was studied in 1967 at the LBNL in their seminal study of nobelium isotopes. The reaction was used in 1990 at the LBNL to study the SF of ²⁵⁶No.

²⁴⁶Cm(¹³C,xn)^259-xNo (4?,5?)

This reaction was studied in 1967 at the LBNL in their seminal study of nobelium isotopes.

²⁴⁶Cm(¹²C,xn)^258-xNo (4,5)

This reaction was studied in 1958 by scientists at the LBNL using a 5% ²⁴⁶Cm curium target. They were able to measure 7.43 MeV decays from ²⁵⁰Fm, associated with a 3 s ²⁵⁴No parent activity, resulting from the 4n channel. The 3 s activity was later reassigned to ²⁵²No, resulting from reaction with the predominant ²⁴⁴Cm component in the target. It could however not be proved that it was not due to the contaminant ^250mFm, unknown at the time. Later work in 1959 produced 8.3 MeV alpha particles with a half-life of 3 s and a 30% SF branch. This was initially assigned to ²⁵⁴No and later reassigned to ²⁵²No, resulting from reaction with the ²⁴⁴Cm component in the target. The reaction was restudied in 1967 and activities assigned to ²⁵⁴No and ²⁵³No were detected.

²⁴⁴Cm(¹³C,xn)^257-xNo (x=4)

This reaction was first studied in 1957 at the Nobel Institute in Stockholm. The scientists detected 8.5 MeV alpha particles with a half-life of 10 minutes. The activity was assigned to ²⁵¹No or ²⁵³No. The results were later dismissed as background. The reaction was repeated by scientists at the LBNL in 1958 but they were unable to confirm the 8.5 MeV alpha particles. The reaction was further studied in 1967 at the LBNL and an activity assigned to ²⁵³No was measured.

²⁴⁴Cm(¹²C,xn)^256-xNo (x=4,5)

This reaction was studied in 1958 by scientists at the LBNL using a 95% ²⁴⁴Cm curium target. They were able to measure 7.43 MeV decays from ²⁵⁰Fm, associated with a 3 s ²⁵⁴No parent activity, resulting from the reaction (²⁴⁶Cm,4n). The 3 s activity was later reassigned to ²⁵²No, resulting from reaction (²⁴⁴Cm,4n). It could however not be proved that it was not due to the contaminant ^250mFm, unknown at the time. Later work in 1959 produced 8.3 MeV alpha particles with a half-life of 3 s and a 30% SF branch. This was initially assigned to ²⁵⁴No and later reassigned to ²⁵²No, resulting from reaction with the ²⁴⁴Cm component in the target. The reaction was restudied in 1967 at the LBNL and an new activity assigned to ²⁵¹No was measured.

²⁵²Cf(¹²C,αxn)^260-xNo (x=3?)

This reaction was studied at the LBNL in 1961 as part of their search for element 104. They detected 8.2 MeV alpha particles with a half-life of 15 s. This activity was assigned to a Z=102 isotope. Later work suggests an assignment to ²⁵⁷No, resulting most likely from the α3n channel with the ²⁵²Cf component of the californium target.

²⁵²Cf(¹¹B,pxn)^262-xNo (x=5?)

This reaction was studied at the LBNL in 1961 as part of their search for element 103. They detected 8.2 MeV alpha particles with a half-life of 15 s. This activity was assigned to a Z=102 isotope. Later work suggests an assignment to ²⁵⁷No, resulting most likely from the p5n channel with the ²⁵²Cf component of the californium target.

²⁴⁹Cf(¹²C,αxn)^257-xNo (x=2)

This reaction was first studied in 1970 at the LBNL in a study of ²⁵⁵No. It was studied in 1971 at the Oak Ridge Laboratory. They were able to measure coincident Z=100 K X-rays from ²⁵⁵No, confirming the discovery of the element.

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

²⁴⁹No

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.

Popular culture

Nobelium was the most recent element "of which the news had come to Harvard" when Tom Lehrer wrote " The Elements Song" and was therefore the element with the highest atomic number to be included.