Four new elements added to periodic table

The periodic table of elements has four new entries, meaning its seventh row has finally been completed. The new elements were discovered by chemists in Japan and a joint US-Russian mission.

The four additions - which have the atomic numbers 113, 115, 117 and 118 - have been temporarily named ununtrium, ununpentium, ununseptium and ununoctium. The scientists will now be allowed to come up with something more poetic.

The discoveries mean that textbooks around the world were rendered out of date on 30 December 2015, when they were verified by the International Union of Pure and Applied Chemistry (IUPAC), The Guardian says.

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They are the first elements to be added to the periodic table, which lists all known chemical elements by atomic number (the number of protons each has in its nucleus), since 2011, when 114 and 116 were included.

The man-made elements were created in the lab by a highly technical process of colliding nuclei and monitoring the subsequent radiation. Super-heavy, they exist only briefly.

Elements 115, 117 and 118 were identified by a US-Russian team from the Joint Institute for Nuclear Research in Dubna, Russia, and the Lawrence Livermore National Laboratory in California.

That team also claimed to have found element 113 - but IUPAC has credited its discovery to a group of scientists at the Riken institute in Japan. It will be the first element to have its name chosen in Asia.

There are strict guidelines about the naming of elements: they must be called after a mythological concept, a mineral, a place or country, a property or a scientist.

Kosuke Morita, who led the research at Riken, said the team now planned to "look to the uncharted territory of element 119 and beyond", according to The Guardian.