Tennessine (formerly Ununseptium meaning "one-one-seven-ium" in Latin) is a radioactive superheavy man-made chemical element. It has a symbol Ts and atomic number of 117. It is the second heaviest element of all, and is the second to last element. It is in group 17 in the periodic table, where the halogens are. Its properties are not yet fully known but it is probably a metalloid.  The discovery of tennessine was announced in 2010 by scientists in Russia and the United States. They collaborated and it is the most recently discovered element as of 2019. It is named after the state of Tennessee and it has no uses except research.

History

Before discovery
In 2004, the Joint Institute for Nuclear Research (JINR) team in Dubna, Moscow Oblast, Russia planned an experiment to create element 117. To do this, they needed to fuse the elements berkelium (element 97) and calcium (element 20). However, the American team at Oak Ridge National Laboratory, the only producer of berkelium in the world, had stopped making berkelium for a while. So, they created the element 118 first using californium (element 98) and calcium.

The Russian team wanted to use berkelium because the isotope of calcium used in the experiment, calcium-48, has 20 protons and 28 neutrons. This is the lightest stable or almost stable nucleus (the center of an atom) with much more neutrons than protons. Zinc-68 is the second-lightest nucleus of this kind, but it is heavier than calcium-48. Since tennessine has 117 protons, they need another atom with 97 protons to be combined with the calcium atom, and berkelium has 97 protons.

In the experiment, the berkelium is made into a target and the calcium is fired in the form of a beam to the berkelium target. The calcium beam is created in Russia by removing the small amount of calcium-48 from natural calcium using chemical means. The nuclei that is made after the experiment will be heavier and is nearer to the island of stability. This is the idea that some very heavy atoms can be quite stable.

Discovery of Tennessine

In 2008, the American team started again to create berkelium, and they told the Russian team about it. The program made 22 milligrams of berkelium, and this is enough for the experiment. Soon after, the berkelium was cooled in 90 days and was made more pure by chemical means in 90 more days. The berkelium target had to be taken to Russia quickly because the half-life of the isotope of berkelium used, berkelium-249, is only 330 days. In other words, after 330 days, half of all the berkelium will no longer be berkelium. Actually, if the experiment did not start six months after the target was made, it would have been cancelled because they did not have enough berkelium for the experiment. In summer 2009, the target was packed into five lead containers and was sent by a commercial flight from New York to Moscow.

Both teams had to face the bureaucratic obstacle between America and Russia before they send the berkelium target to allow it to arrive in Russia on time. However, there were still problems: Russian customs did not let the berkelium target get into the country twice due to missing or incomplete paperwork. Even though the target went over the Atlantic Ocean five times, the whole journey only took a few days. When the target finally got into Moscow, it was sent to Dimitrovgrad, Ulyanovsk Oblask. Here, the target was placed on a thin titanium film (layer). This film was then sent to Dubna where it was placed inside the JINR particle accelerator. This particle accelerator is the most powerful particle accelerator in the world for the creation of superheavy elements.

The experiment began in June 2009. In January 2010, the scientists at the Flerov Laboratory of Nuclear Reactions announced within the laboratory that they had found the decay of a new element with atomic number 117 through two decay chains. The odd-odd isotope does 6 alpha decays before doing a spontaneous (sudden) fission. The odd-even isotope does 3 alpha decays before fission. On 9 April 2010, an official report was released in the Physical Review Letters journal. It showed that the isotopes that were mentioned in the decay chains were 294Ts and 293Ts. The isotopes were made as follows:

249Bk + 48Ca → 297Ts* → 294Ts + 3 n (1 event)
249Bk + 48Ca → 297Ts* → 293Ts + 4 n (5 events)

Chemistry 
The chemistry of Tennessine is currently unknown. However, chemists can predict how the element would be like using chemistry from the other halogens. Tennessine is most likely supposed to be a member of group 17 in the periodic table, below the five halogens: fluorine, chlorine, bromine, iodine, and astatine. Each of them has seven valence electrons. For tennessine, being in the seventh period (row) of the periodic table, going down the halogen group would predict a valence electron configuration of 7s27p5, and it would therefore be expected to behave kind of like to the halogens in many ways.

Uses 
There are no uses for Tennessine because of how short lived it is and its radioactivity.

References

Other websites 

WebElements.com - Uus
Apsidium - Tennessine
Theory of atomic-mass calculation

Chemical elements
Nonmetals
Halogens