Posters in chemistry labs are in need of an update. The periodic table now has four new elements, completing its seventh row.
The International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Pure and Applied Physics (IUPAP) have recognised the discoveries of elements 113, 115, 117 and 118. They were created by teams of researchers in Japan, Russia and the US, who smashed lighter nuclei into each other. The resulting superheavy elements, like others of their kind, exist for only a fraction of a second before decaying into lighter atoms.
Their discoverers will be invited to propose names for these elements, which must derive from mythology or the names of minerals, places, properties of the element, or scientists. For now, the new elements have been assigned placeholder names and symbols: ununtrium (Uut), ununpentium (Uup), ununseptium (Uus) and ununoctium (Uuo).
The last time new elements were recognised was in 2011, when the periodic table gained flerovium (114) and livermorium (116).
For new elements to be accepted, there must be multiple detections in different experiments, and ruling on who made the discovery can be controversial.
A collaboration at RIKEN in Wako, Japan, has been credited with finding element 113. A team at the Joint Institute for Nuclear Research in Dubna, Russia, had claimed to have found it in 2003, but their result was ruled inconclusive.
The discovery of the other three new elements has been credited to teams in Russia and the US, working collaboratively.
“The chemistry community is eager to see its most cherished table finally being completed down to the seventh row,” said Jan Reedijk, president of IUPAC’s inorganic chemistry division.
Apart from helping to flesh out the periodic table, the creation of superheavy elements puts theories of atomic structure to the test, and might one day yield stable new elements with strange properties.
Protons and neutrons are thought to occupy shells within the nucleus, and atoms are more likely to be stable if the outer shell is full. Lead (atomic number 82) has a full outer shell, and so most elements heavier than it are unstable.
But heavier elements should include “islands of stability” where the outer shell of the nucleus is once again full. Their huge nuclei would accelerate electrons close to the speed of light, almost certainly resulting in weird chemistry.
Kosuke Morita (pictured above), who led the Japanese group, has his sights set on that goal. “Now that we have conclusively demonstrated the existence of element 113, we plan to look to the uncharted territory of element 119 and beyond, aiming to examine the chemical properties of the elements in the seventh and eighth rows of the periodic table, and someday to discover the island of stability,” he said.