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ununseptium
Ununseptium is a superheavy artificial chemical element with an atomic number of 117 and a temporary symbol of Uus. Also known as eka-astatine or element 117, it is the second-heaviest known element and second-to-last element of the 7th period of the periodic table. , fifteen ununseptium atoms have been observed: six when it was first synthesized in 2010, seven in 2012, and two in 2014.
The discovery of ununseptium was announced in Dubna, Russia, by a Russian–American collaboration in 2010, which makes it the most recently discovered element . One of its daughter isotopes was created directly in 2011, partially confirming the results of the experiment. The experiment itself was repeated successfully by the same collaboration in 2012 and by a joint German–American team in 2014. The Joint Working Party (JWP) of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP), which is in charge of examining claims of discovery of superheavy elements, has made no comment on whether the element can be recognized as discovered. Once it is recognized, the discoverers will be invited to give the element an official name. "Ununseptium" is a temporary systematic element name that is intended to be used until a permanent one is assigned; the working name "element 117" is commonly used by researchers and in the literature.
Ununseptium may be located in the "island of stability", a concept that explains why some superheavy elements are more stable compared to an overall trend of decreasing stability for elements beyond lead on the periodic table. The synthesized ununseptium atoms have lasted tens and hundreds of microseconds. In the periodic table, ununseptium is expected to be a member of group 17, all other members of which are halogens. Some of its properties are likely to be significantly different from those of the halogens due to relativistic effects. Unlike the halogens, ununseptium is likely to neither commonly form anions nor achieve high oxidation states. A few key properties, such as its melting and boiling points and its first ionization energy, are nevertheless expected to follow the periodic trends of the halogens.
==History==
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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