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Ununennium
Ununennium, also known as eka-francium or simply element 119, is the hypothetical chemical element with atomic number 119 and symbol Uue. ''Ununennium'' and ''Uue'' are the temporary systematic IUPAC name and symbol, until a permanent name is decided upon. In the periodic table of the elements, it is expected to be an s-block element, an alkali metal, and the first element in the eighth period.
Ununennium is the element with the lowest atomic number that has not yet been synthesized. Multiple attempts have been made by American, German, and Russian teams to synthesize this element: they have all been unsuccessful, as experimental evidence has shown that the synthesis of ununennium will likely be far more difficult than that of the previous elements, and may even be the penultimate element that can be synthesized with current technology. Its position as the seventh alkali metal suggests that it would have similar properties to the alkali metals, lithium, sodium, potassium, rubidium, caesium, and francium; however, relativistic effects may cause some of its properties to differ from those expected from a straight application of periodic trends. For example, ununennium is expected to be less reactive than caesium and francium and to be closer in behavior to potassium or rubidium, and while it should show the characteristic +1 oxidation state of the alkali metals, it is also predicted to show the +3 oxidation state unknown in any other alkali metal.
==History==
Superheavy elements are produced by nuclear fusion. These fusion reactions can be divided into "hot" and "cold" fusion, depending on the excitation energy of the compound nucleus produced. In hot fusion reactions, very light, high-energy projectiles are accelerated toward very heavy targets (actinides), giving rise to compound nuclei at high excitation energy (~40–50 MeV) that may fission, or alternatively evaporate several (3 to 5) neutrons. In cold fusion reactions (which use heavier projectiles, typically from the fourth period, and lighter targets, usually lead and bismuth), the fused nuclei produced have a relatively low excitation energy (~10–20 MeV), which decreases the probability that these products will undergo fission reactions. As the fused nuclei cool to the ground state, they require emission of only one or two neutrons. However, hot fusion reactions tend to produce more neutron-rich products because the actinides have the highest neutron-to-proton ratios of any elements that can presently be made in macroscopic quantities.
Ununennium and unbinilium (elements 119 and 120) are the lightest elements that have not yet been synthesized, and attempts to synthesize them would push the limits of current technology, due to the decreasing cross sections of the production reactions and their probably short half-lives, expected to be on the order of microseconds.〔〔 Heavier elements would likely be too short-lived to be detected with current technology.〔 Previously, important help (characterized as "silver bullets") in the synthesis of superheavy elements came from the deformed nuclear shells around hassium-270 which increased the stability of surrounding nuclei, and the existence of the quasi-stable neutron-rich isotope calcium-48 which could be used as a projectile to produce more neutron-rich isotopes of superheavy elements.〔 The more neutron-rich a superheavy nuclide is, the closer it is expected to be to the sought-after island of stability. Even so, the synthesized isotopes still have fewer neutrons than those expected to be in the island of stability.〔 〕 Furthermore, using calcium-48 to synthesize ununennium would require a target of einsteinium-253 or −254, which is very difficult to produce in sufficiently large quantities. More practical production of further superheavy elements would require projectiles heavier than 48Ca.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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