Ununseptium is a hypothetical chemical element which had not been successfully confirmed by 2008, although several scientific teams had plans for synthesizing it. Despite the fact that the existence of this element has not yet been verified, the scientific community can draw some conclusions about it, and it is safe to say that it really does exist; if it didn't, the entire periodic table would have to be reworked.
This element is among a group of elements known as transactinides. Transactinides are the heaviest elements known to man, and they share a number of chemical properties which ununseptium will probably possess. Transactinides are all extremely unstable, which makes them difficult to study, and they are also radioactive. These elements cannot be found in nature, because they exist for such brief periods of time; to study them, scientists must synthesize them with the assistance of a linear accelerator.
Elements like ununseptium are synthesized by bombarding more stable elements or their isotopes with isotopes of other elements. The collisions caused during this bombardment can cause heavier elements to emerge, albeit usually briefly. Scientists take advantage of the brief appearance of these elements to make as many observations about them as possible. Given that only a few atoms of a transactinide element are produced at any given time with this technique, you can imagine that the equipment involved is extremely precise and very expensive.
This element has been given the name “ununseptium” as a placeholder, in a reference to its atomic number, 117. Given that elements 116 and 118 have been discovered, the scientific community is fairly certain that ununseptium will be identified at some point; in 2001, scientists at the University of California, Berkeley thought that they had found ununseptium, but they were later forced to retract the claim. Researchers at Dubna in Russia have proposed bombarding calcium with berkelium to yield ununseptium.
“Ununseptium” is a systematic element name which follows a set of guidelines established by the International Union of Pure and Applied Chemistry (IUPAC). The IUPAC uses temporary systematic element names to identify elements until their discoveries are confirmed and the IUPAC can determine who deserves the credit of discovery and the honor of proposing a name. Systematic element names are derived from the element's atomic number, with the suffix “-ium” to make the element conform with the rest of the periodic table. Ununsept, as you might imagine, means “one one seven” in Latin; the temporary symbol for this element is Uus.