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Roentgenium (pronounced /rɛntˈɡɛniəm/ rent-GEN-ee-əm or /rʌntˈɡɛniəm/ ( listen) runt-GEN-ee-əm) is a synthetic radioactive chemical element with the symbol Rg and atomic number 111. It is placed as the heaviest member of the group 11 (IB) elements, although a sufficiently stable isotope is not known at this time that would allow its position as a heavier homologue of gold to be confirmed.

Roentgenium was called unununium before it was formally discovered.

Roentgenium was first observed in 1994 and several isotopes have been synthesized since its first discovery. The most stable known isotope is 281Rg with a half-life of ~20 seconds, which decays by spontaneous fission, like many other N=170 isotones.

Official discovery

Roentgenium was officially discovered by Peter Armbruster, Gottfried Münzenberg, and their team working at the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany on December 8, 1994.[1] Only three atoms of it were observed (all 272Rg), by the cold fusion between nickel ions and a bismuth target in a linear accelerator:

20983Bi + 6428Ni → 272111Rg + 10n

In 2001, the IUPAC/IUPAP Joint Working Party (JWP) concluded that there was insufficient evidence for the discovery at that time.[2] The GSI team repeated their experiment in 2000 and detected a further 3 atoms.[3][4] In their 2003 report, the JWP decided that the GSI team should be acknowledged as the discoverers.[5]


The name roentgenium (Rg) was proposed by the GSI team[6] in honor of the German physicist Wilhelm Conrad Röntgen, and was accepted as a permanent name on November 1, 2004.[7] Previously the element was known under the temporary IUPAC systematic element name unununium, Uuu.
Isotopes and nuclear properties

Target-projectile combinations leading to Z=111 compound nuclei

The below table contains various combinations of targets and projectiles (both at max no. of neutrons) which could be used to form compound nuclei with Z=111.
Target Projectile CN Attempt result
208Pb 65Cu 273Rg Successful reaction
209Bi 64Ni 273Rg Successful reaction
232Th 45Sc 277Rg Reaction yet to be attempted
231Pa 48Ca 279Rg Reaction yet to be attempted
238U 41K 280Rg Reaction yet to be attempted
237Np 40Ar 277Rg Reaction yet to be attempted
244Pu 37Cl 281Rg Reaction yet to be attempted
243Am 36S 279Rg Reaction yet to be attempted
248Cm 31P 279Rg Reaction yet to be attempted
249Bk 30Si 279Rg Reaction yet to be attempted
249Cf 27Al 276Rg Reaction yet to be attempted
Cold fusion

This section deals with the synthesis of nuclei of roentgenium by so-called "cold" fusion reactions. These are processes which create compound nuclei at low excitation energy (~10-20 MeV, hence "cold"), leading to a higher probability of survival from fission. The excited nucleus then decays to the ground state via the emission of one or two neutrons only.
209Bi(64Ni,xn)273−xRg (x=1)

First experiments to synthesize element 111 were performed by the Dubna team in 1986 using this cold fusion reaction. No atoms were identified that could be assigned to atoms of element 111 and a production cross-section limit of 4 pb was determined. After an upgrade of their facilities, the team at GSI successfully detected 3 atoms of 272Rg in their discovery experiment.[1] A further 3 atoms were synthesized in 2000.[3] The discovery of roentgenium was confirmed in 2003 when a team at RIKEN measured the decays of 14 atoms of 272Rg during the measurement of the 1n excitation function.[8]
208Pb(65Cu,xn)273−xRg (x=1)

In 2004, as part of their study of odd-Z projectiles in cold fusion reactions, the team at LBNL detected a single atom of 272Rg in this new reaction.[9][10]
As a decay product

Isotopes of roentgenium have also been observed in the decay of heavier elements. Observations to date are outlined in the table below:
Evaporation residue Observed Rg isotope
288Uup 280Rg [11]
287Uup 279Rg [11]
282Uut 278Rg [12]
278Uut 274Rg [12]
Chronology of isotope discovery
Isotope Year discovered Discovery reaction
272Rg 1994 209Bi(64Ni,n)
273Rg unknown
274Rg 2004 209Bi(70Zn,n) [12]
275Rg unknown
276Rg unknown
277Rg unknown
278Rg 2006 237Np(48Ca,3n) [12]
279Rg 2003 243Am(48Ca,4n) [11]
280Rg 2003 243Am(48Ca,3n) [11]
281Rg 2009 249Bk(48Ca,4n)
282Rg 2009 249Bk(48Ca,3n)

Nuclear isomerism

Two atoms of 274Rg have been observed in the decay chains starting with 278Uut. The two events occur with different energies and with different lifetimes. In addition, the two entire decay chains appear to be different. This suggests the presence of two isomeric levels but further research is required.

The direct production of 272Rg has provided four alpha lines at 11.37, 11.03, 10.82, and 10.40 MeV. The GSI measured a half-life of 1.6 ms whilst recent data from RIKEN hav given a half-life of 3.8 ms. The conflicting data may be due to isomeric levels but the current data are insufficient to come to any firm assignments.
Chemical yields of isotopes
Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing roentgenium isotopes directly. Data in bold represent maxima derived from excitation function measurements. + represents an observed exit channel.
Projectile Target CN 1n 2n 3n
64Ni 209Bi 273Rg 3.5 pb, 12.5 MeV
65Cu 208Pb 273Rg 1.7 pb, 13.2 MeV
Chemical properties
Electronic structure (relativistic)

The stable group 11 elements, copper, silver, and gold all have an outer electron configuration nd10(n+1)s1. For each of these elements, their first excited state has a configuration nd9(n+1)s2. Due to spin-orbit coupling between the s electrons, this state is split into a pair of energy levels. For copper, the difference in energy between the ground state and lowest excited state causes the metal to appear reddish. For silver, the energy gap widens and it becomes silvery. However, as Z increases, the excited levels are stabilised by relativistic effects and in gold the energy gap decreases again and it appears gold. For roentgenium, calculations indicate that the 6d97s2 level is stabilised to such an extent that it becomes the ground state. The resulting energy difference between the new ground state and the first excited state is similar to that of silver and roentgenium is expected to be silvery in appearance.[13]

Extrapolated chemical properties
Oxidation states

Element 111 is projected to be the ninth member of the 6d series of transition metals and the heaviest member of group 11 (IB) in the Periodic Table, below copper, silver, and gold. Each of the members of this group show different stable states. Copper forms a stable +2 state, whilst silver is predominantly found as silver(I) and gold as gold(III). Copper(I) and silver(II) are also relatively well-known. Roentgenium is therefore expected to predominantly form a stable +3 state.


The heavier members of this group are well known for their lack of reactivity or noble character. Silver and gold are both inert to oxygen, but are attacked by the halogens. In addition, silver is attacked by sulfur and hydrogen sulfide, highlighting its higher reactivity compared to gold. Roentgenium is expected to be even more noble than gold and can be expected to be inert to oxygen and halogens. The most-likely reaction is with fluorine to form a trifluoride, RgF3.

See also

* Island of stability


1. ^ a b Hofmann, S.; Ninov, V.; He�berger, F. P.; Armbruster, P.; Folger, H.; M�nzenberg, G.; Sch�tt, H. J.; Popeko, A. G. et al. (1995). "The new element 111". Zeitschrift für Physik a Hadrons and Nuclei 350: 281. doi:10.1007/BF01291182.
2. ^ Karol et al.; Nakahara, H.; Petley, B. W.; Vogt, E. (2001). "On the discovery of the elements 110–112". Pure Appl. Chem. 73 (6): 959–967. doi:10.1351/pac200173060959. http://iupac.org/publications/pac/2001/pdf/7306x0959.pdf.
3. ^ a b Hofmann, S.; Heßberger, F.P.; Ackermann, D.; Münzenberg, G.; Antalic, S.; Cagarda, P.; Kindler, B.; Kojouharova, J. et al. (2002). "New results on elements 111 and 112". The European Physical Journal A 14: 147. doi:10.1140/epja/i2001-10119-x.
4. ^ Hofmann et al.. "New results on element 111 and 112". GSI report 2000. http://www.gsi.de/informationen/wti/library/scientificreport2000/Nuc_St/7/ar-2000-z111-z112.pdf. Retrieved 2008-03-02.
5. ^ "Karol et al.". Pure Appl. Chem. 75 (10): 1601–1611. 2003. http://iupac.org/publications/pac/2003/pdf/7510x1601.pdf.
6. ^ Corish et al.. "Name and symbol of the element with atomic number 111". IUPAC Provisional Recommendations. http://iupac.org/reports/provisional/abstract04/Corish_pr111.pdf. Retrieved 2008-03-02.
7. ^ Corish et al.; Rosenblatt, G. M. (2004). "Name and symbol of the element with atomic number 111". Pure Appl. Chem. 76 (12): 2101–2103. doi:10.1351/pac200476122101. http://iupac.org/publications/pac/2004/pdf/7612x2101.pdf.
8. ^ Morita, K; Morimoto, K; Kaji, D; Goto, S; Haba, H; Ideguchi, E; Kanungo, R; Katori, K et al. (2004). "Status of heavy element research using GARIS at RIKEN". Nuclear Physics A 734: 101. doi:10.1016/j.nuclphysa.2004.01.019.
9. ^ Folden, C. M. (2004). "Development of an Odd-Z-Projectile Reaction for Heavy Element Synthesis: ^{208}Pb(^{64}Ni,n)^{271}Ds and ^{208}Pb(^{65}Cu,n)^{272}111". Physical Review Letters 93: 212702. doi:10.1103/PhysRevLett.93.212702.
10. ^ "Development of an Odd-Z-Projectile Reaction for Heavy Element Synthesis: 208Pb(64Ni,n)271Ds and 208Pb(65Cu,n)272111", Folden et al., LBNL repositories. Retrieved on 2008-03-02
11. ^ a b c d see ununpentium for details
12. ^ a b c d see ununtrium for details
13. ^ Turler, A. (2004). "Gas Phase Chemistry of Superheavy Elements". Journal of Nuclear and Radiochemical Sciences 5 (2): R19–R25. http://wwwsoc.nii.ac.jp/jnrs/paper/JN52/j052Turler.pdf.

External links

* WebElements.com: Roentgenium
* IUPAC: Proposal of name roentgenium for element 111
* IUPAC: Element 111 is named roentgenium
* Apsidium: Roentgenium 111

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