Another Step Toward the Completion of the Periodic Table

Another Step Toward the Completion of the Periodic Table

I wonder how many times students have been directed to complete a table for homework or on an exam. Chemists have an incomplete table that they are trying to complete: the Periodic Table of the Elements, or the Periodic Table, for short. Uranium, element number 92 is the last naturally occurring element in the Periodic Table. Elements beyond number 92, called the transuranium elements, have all been produced in laboratories. The first transuranium element, neptunium (#93) was produced in 1940 at the University of California, Berkeley, by Edwin McMillan and Phillip Abelson by exposing uranium oxide to neutrons from a cyclotron. The last one, copernicium (#112) was officially recognized in 2009.

On June 6, 2011, the Joint Working Party on the Discovery of Elements of the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) announced the addition of two new elements to the Periodic Table—element 114 and element 116. For now, element 114 is called ununquadium and element 116 is called ununhexium. These names are based on their atomic numbers. By officially acknowledging the collaboration between researchers from Lawrence-Livermore National Laboratory in California and Russia’s Joint Institute for Nuclear Research in Dubna, these researchers will get to suggest names for the new elements. The names will go through a review process before being adopted and the elements will be assigned a symbol by the IUPAC Council.

Scientists produced these elements by bombarding curium (#96) atoms with calcium (#20) nuclei. In a few milliseconds, element 116 decays into element 114 which lasts about half a second before decaying into copernicium (#112). In other experiments element 114 was produced by bombarding plutonium (#94) with calcium nuclei. Notice that 96 + 20 = 116 and 94 + 20 = 114.

There are three more elements waiting to be recognized: 113, 115, and 118. According to IUPAC, “Review of the claims associated with elements 113, 115, and 118 are at this time not conclusive and evidences have not met the criteria for discovery.” As soon as I hear anything more, I will let you know.