The global agency for chemistry has formally added two new elements to the periodic table but the substances are so unstable, they exist for less than a second before decaying.

The two elements, known only as 114 and 116 until they are officially named, are now the heaviest elements on the periodic table with atomic weights of 289 and 292 atomic mass units.

The previous heavyweight winner was copernicium, with an atomic weight of 285. The two new elements are much heavier than the heaviest naturally occurring element, uranium (238).

International Union of Pure and Applied Chemistry (IUPAC) said in a statement that it had confirmed the discovery of the new elements made by scientists from the Joint Institute for Nuclear Research in Dubna, Russia and from Lawrence Livermore, in California, the U.S.

The first reports of these elements were made in 2004 and it has taken IUPAC until now to confirm the discoveries.

The element 114 is made by crashing nuclei together from Calcium 48 and Plutonium 242, while 116 is made by collisions of nuclei from Calcium 48 and Curium 245.

“This is not something you can do in your average high school laboratory. To create these elements, you need huge equipment worth millions of dollars to collide two fairly heavy nuclei together and hope they might give you a new element,” said Professor Anthony Baker, Head of the School of Chemistry and Forensic Science at the University of Technology, Sydney.

“It’s worth remembering that they don’t discover large lumps of this stuff. These things that they discover, you can count the number of atoms on one hand,” he said.

The new substances are so radioactive and unstable, they last less than a second before breaking up into smaller atoms. No-one yet knows how they could be used in practice.

“It’s not something you can put in a bottle and sell in a shop,” said Professor Baker. “No-one’s actually discovered how they react chemically. They are a curiosity at this stage.”

The collaborative work between chemists in Russia and the U.S. was an interesting post-Cold War phenomenon, said Professor Baker.

“For a long time during the Cold War years you would have had the labs in the U.S. and Russia going at it hammer and tongs. But now in places like the Dubna centre, you now have the Russians and the Americans working together.”