Nobelium

Nobelium is the second-to-last actinide, with the electron configuration 5f14 7s2. That completely filled 5f subshell gives it the most unusual chemistry in its series: while nearly every other actinide prefers the +3 oxidation state in water, nobelium prefers +2. Removing a third electron would mean breaking into the stable, filled 5f14 shell, so No3+ is a strong oxidizing agent that readily grabs an electron back.

This makes nobelium behave in solution more like the alkaline-earth ions, such as Ca2+ and Sr2+, than like its actinide neighbors. Only atom-at-a-time experiments are possible: the longest-lived isotope, nobelium-259, has a half-life of about 58 minutes, and production rates are a few atoms per minute at best. Even so, laser spectroscopy at GSI, beginning in 2016, has measured its atomic energy levels and the size of its nucleus, the heaviest element studied this way at the time.

Discovery

Nobelium's discovery is one of the most disputed in chemistry. A team at the Nobel Institute in Stockholm claimed it in 1957 and proposed the name nobelium after Alfred Nobel; that result could not be reproduced. Berkeley reported it in 1958, but its isotope assignments were wrong. Careful work at Dubna by Georgy Flerov's group between 1963 and 1966 was later judged the conclusive discovery. IUPAC nevertheless kept the established name, nobelium, in 1997.