Roentgenium

Roentgenium is a chemical element from group 11 of the periodic table whose symbol is Rg and its atomic number is 111.

It was discovered in 1994 by German scientists in Darmstadt. In November 2004, it received the name of roentgenium in honor of Wilhelm Conrad Röntgen (1845-1923), Nobel Prize in Physics, discoverer of X-rays. Roentgenium is obtained by bombarding bismuth (Bi) sheets with ions of nickel (Ni), decaying in 15 milliseconds.

Isotopes

Roentgenium has no stable or natural isotopes. Various radioactive isotopes have been synthesized in the laboratory, either by fusing the nuclei of lighter elements or as decay intermediates of heavier elements. Nine different isotopes of roentgenium with atomic masses 272, 274, 278-283, and 286 (283 and 286 unconfirmed) have been reported, and for two of which, roentgenium-272 and roentgenium-274, have known but unconfirmed metastable states.. All of these decay via alpha decay or spontaneous fission, although ²⁸⁰Rg can also have an electron capture branch.

Stability and half-life periods

All isotopes of roentgenium are extremely unstable and radioactive; in general, heavier isotopes are more stable than lighter ones. The most stable known roentgenium isotope, ²⁸²Rg, is also the heaviest known roentgenium isotope; it has a half-life of 100 seconds. The unconfirmed ²⁸⁶Rg is even heavier and appears to have an even longer half-life of about 10.7 minutes, which would make it one of the longest-lived superheavy nuclides known; similarly, the unconfirmed ²⁸³Rg appears to have a long half-life of approximately 5.1 minutes. The isotopes ²⁸⁰Rg and ²⁸¹Rg have also been reported to have half-lives greater than one second. The remaining isotopes have half-lives in the millisecond range.

Estimated Properties

Apart from the properties of the nucleus, no properties of roentgenium or its compounds have been determined; this is due to its extremely limited and expensive production and the fact that roentgenium (and its predecessors) decay very quickly. The properties of the metal roentgenium remain unknown and only predictions are available.

Chemical Properties

Roentgenium is the ninth member of the 6d series of transition metals. Estimates of its ionization potential, atomic radius, and ionic radius are similar to those of its lighter counterpart gold, implying that the properties The basic elements of roentgenium will resemble those of the other group 11 elements, that is, copper, silver, and gold; however, it is also expected to display several differences from its lighter counterparts.

Roentgenium is predicted to be a noble metal. The drop potential of 1.9 V for the Rg³⁺/Rg pair is greater than the 1.5 V for the Au³⁺/Au pair. Roentgenium's first predicted ionization energy of 1020 kJ/mol nearly matches that of the noble gas radon at 1037 kJ/mol. Based on the more stable oxidation states of the lightest group 11 elements, roentgenium is predicted to show stable +5 and +3 oxidation states, with a less stable +1 state. The +3 state is expected to be the most stable. Roentgenium(III) is expected to have comparable reactivity to gold(III), but it should be more stable and form a greater variety of compounds. Gold also forms a somewhat stable −1 state due to relativistic effects, and it has been suggested that roentgenium might as well: however, the electron affinity of roentgenium is expected to be around 1.6 eV, significantly lower than that of gold. gold value of 2.3 eV, so roentgenids may not be stable or even possible. The 6d orbitals are destabilized by relativistic effects and spin-orbit interaction near the end of the fourth transition metal series, making the high oxidation state roentgenium (V) more stable than its lighter counterpart, gold. (V) (known only in gold pentafluoride, Au₂F₁₀) since 6d electrons participate in bonding to a greater extent. Spin-orbit interactions stabilize molecular roentgenium compounds with more 6d bonding electrons; for example, RgF₆^- is expected to be more stable than RgF₄ ^-, which is expected to be more stable than RgF ₂ ^-. The stability of RgF ₆ ^- is homologous to that of AuF ₆ ^-; the silver analogue AgF ₆ ^- is unknown and is expected to be only marginally stable to decay in AgF₄ ^- and F₂. Furthermore, Rg₂F₁₀ is expected to be stable to decay, exactly analogous to Au₂F₁₀ while Ag₂F₁₀ should be unstable to decomposition into Ag₂F₆ and F ₂ . Gold heptafluoride, AuF₇, is known as a gold(V) difluoride complex AuF₅ F₂, which is more low in energy than would be a true gold(VII) heptafluoride; Instead, RgF₇ is calculated to be more stable as true roentgenium(VII) heptafluoride, although its decomposition to Rg₂F_{10 and F2 releasing a small amount of energy at room temperature. Roentgenium(I) is expected to be difficult to obtain. Gold readily forms the complex cyanide Au(CN)−
2, which is used in the extraction of ore through the gold cyanidation process; Roentgenium is expected to do the same and form Rg(CN)−
2.}

The probable chemistry of roentgenium has received more interest than that of the previous two elements, meitnerium and darmstadtium, as the s-valence subshells of group 11 elements are expected to contract relativistically more strongly in roentgenium. Calculations on the molecular compound RgH show that relativistic effects double the strength of the roentgenium-hydrogen bond, although spin-orbit interactions also weaken it by 0.7 eV (16 kcal/mol). The compounds AuX and RgX were also studied, where X = F, Cl, Br, O, Au or Rg.[2][62] Rg+ is predicted to be the softest metal ion, even softer than Au+, although there is disagreement as to whether it would behave as an acid or as a base.[63][64] In aqueous solution, Rg+ would form the water ion [Rg(H2O)2]+, with an Rg–O bond distance of 207.1 pm. It is also expected to complex Rg(I) with ammonia, phosphine, and hydrogen sulfide.

Physical properties and its atom

Roentgenium is expected to be solid under normal conditions and to crystallize in the body-centered cubic structure, unlike its lighter congeners which crystallize in the face-centered cubic structure, because it is expected to have electron charge densities different from theirs. It should be a very heavy metal with a density of around 22-24 g/cm³; for comparison, the densest known element whose density has been measured, osmium, has a density of 22.61 g/cm³.

The stable group 11 elements, copper, silver, and gold, all have an outer electron configuration (n−1)d¹⁰ns¹. For each of these elements, the first excited state of its atoms has a configuration (n−1)d⁹ns². Due to the spin-orbit coupling between the d electrons, this state is divided into a pair of energy levels. in the case of copper, the difference in energy between the ground state and the lowest excited state makes the metal appear reddish. in the case of silver, the energy gap widens and the color becomes silver. However, as the atomic number increases, the excited levels stabilize due to relativistic effects and in gold the energy gap decreases again and the color makes gold appear. In the case of roentgenium, calculations indicate that the 6d⁹7s² level stabilizes to such an extent that it becomes the ground state and the 6d^{10 level} 7s¹ becomes the first excited 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 have a silvery appearance. The atomic radius of roentgenium is expected to be around 138 pm.

Additional bibliography

• Audi, G.; Kondev, F. G.; Wang, M. et al. (2017). «The NUBASE2016 evaluation of nuclear properties». Chinese Physics C (in English) 41 (3): 30001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
• Beiser, A. (2003). Concepts of modern physics (in English) (6th edition). McGraw-Hill. ISBN 978-0-07-2448-1. OCLC 48965418.
• Hoffman, D.C.; Ghiorso, A.; Seaborg, G.T. (2000). The Transuranium People: The Inside Story (in English). World Scientific. ISBN 978-1-78-326244-1.
• Kragh, H. (2018). From Transuranic to Superheavy Elements: A Story of Dispute and Creation (in English). Springer. ISBN 978-319-75813-8.
• Zagrebaev, V.; Karpov, A.; Greiner, W. (2013). «Future of superheavy element research: Which nuclei could be synthesized within the next few years?». Journal of Physics: Conference Series (in English) 420 (1): 012001. Bibcode:2013JPhCS.420a2001Z. ISSN 1742-6588. S2CID 55434734. arXiv:1207.5700. doi:10.1088/1742-6596/420/1/012001.