Neptunium is the last naturally occurring element, while plutonium, which is created in supernovae (and by irradiating uranium), has played a highly significant role in our history. From this point onwards, the elements become increasingly arcane – they can only be created on Earth by bombarding other elements with particles in a handful of high-tech laboratories around the world, and they are all highly unstable and rapidly decay back into uranium and other elements. So, rather than devote a whole section to each of them, here are a few key facts, with the chemical symbols and atomic numbers in brackets.
Americium
Americium (Am 95) was once present on Earth, having been formed in the natural nuclear reactions beneath Gabon, but the longest-lived isotope (americium-247) has a half-life of 7,370 years, meaning that supply has all decayed. It was first manufactured in 1944 at the University of Chicago by a team led by Glenn Seaborg.
Curium (Cm 96), which was named after the Curies, had also been discovered by a group led by Glenn Seaborg, this time at Berkeley earlier in 1944. Seaborg actually made the announcement when he appeared on a children’s radio show in November 1945. It has been used as a power source on missions to space.
Berkelium
Berkelium (Bk 97) was made by bombarding americium-241 with helium particles in 1949. It took nine years to make enough of the element to be seen with the naked eye. It was named after Berkeley, where it was created.
Californium
Californium (Cf 98) continued the theme, being named after the state where it was created by bombarding curium atoms with helium. It is used in detectors that identify gold and silver ores, and for detecting metal fatigue in aeroplanes.
Einsteinium and Fermium
Einsteinium (Es 99) and Fermium (Fm 100) were discovered in fall-out material from the nuclear test in November 1952 at Bikini Atoll. Both were initially kept secret and only announced as new elements in 1955. The elements with a higher atomic number than 100 are called the ‘transfermium elements’.
Mendelevium (Md 101) is rather splendidly named after the creator of the periodic table. When it was first created in the Berkeley cyclotron, just seventeen atoms were produced. Like most of the heavier elements, it is only used for research purposes.
Nobelium
Nobelium (No 102) was the cause of a scientific spat. It was discovered, but not announced, in 1956 by scientists at the Institute of Atomic Energy, Moscow. After it was subsequently made at the Nobel Institute in Stockholm (thus the name) and also in Berkeley, years of debate followed as to who the real discoverers were.
Lawrencium, Rutherfordium and Dubnium
Lawrencium (Lr 103), Rutherfordium (Rf 104), Dubnium (Db 105) – Russian and American teams also squabbled over who discovered elements 103, 104 and 105. Element 103 is named after Ernest Lawrence, who invented the cyclotron particle accelerator. The Russians first made the element now known as Rutherfordium (named after the physicist Ernest Rutherford) in 1964 by bombarding plutonium with neon. A similar technique led to the discovery of element 105, which the Russians called neilsbohrium, and the Americans hahnium. The IUPAC eventually ruled it should be called dubnium after Dubna, home of the Russian Joint Institute for Nuclear Research (JINR). Lawrencium is the last actinide: elements from 104 upwards can be called transactinides or super-heavy elements.
Seaborgium
Seaborgium (Sg 106), named after Glenn Seaborg, was first made in 1970 by bombarding californium with oxygen, and again in 1974 by bombarding lead with chromium. Only a small number of atoms have ever been produced.
Bohrium, Hassium, Meitnerium, Darmstadtium, Roentgenium and Copernicum
Bohrium (Bh 107) was probably first made at the JINR in 1975, but the first sighting production was at the German nuclear research institute (the Gesellschaft für Schwerionenforschung or GSI) after bismuth was bombarded with chromium in a cold fusion process (meaning it happened at or near to room temperature). The same team also produced the first tiny amounts of Hassium (Hs 108), Meitnerium (Mt 109), Darmstadtium (Ds 110), Roentgenium (Rg 111) and Copernicum (Cn 112).
Nihonium
Nihonium (Nh 113) was produced by scientists from RIKEN (the Institute of Physical and Chemical Research) in Japan in 2004, and very little is known about it to this day.
Flerovium, Moscovium, Livermorium, Tennessine and Oganesson
The last five elements were all created at the JINR by Yuri Oganessian and his team of scientists. They are Flerovium (Fl 114), Moscovium (Mc 115), Livermorium (Lv 116), Tennessine (Ts 117) and Oganesson (Og 118, named after the man himself). Tennessine was the last of the 118 elements to be synthesized, in 2010. All of these elements are highly unstable and have only been synthesized in tiny quantities, so we know relatively little about them.