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Actinium, element 89, was discovered by French chemist André-Louis Debierne in 1899, a year after the Curies discovered radium. Debierne announced his discovery the following year, naming the new radioactive element after the Greek άκτις (actis), meaning beam or ray. In this way, it is the Greek equivalent of the Curies’ Latin radium.¹

¹Oxford English Dictionary, actinium, 2nd Edition, 1989, Oxford University Press, accessed 15 November 2009, http://dictionary.oed.com/cgi/entry/50002167. 

See radium.

See radium.

See radium.

Radium, element 88, was discovered by Marie and Pierre Curie in 1898. The Curies dubbed the new element so because of its radioactive properties. The rad- is from the Latin radius, or ray. The first known English appearance of the word is in a January 1899 article by the pair.¹ The chemical symbol for radium is Ra. The Curies were awarded the 1903 Nobel Prize in Physics for their work on radioactivity, and Marie was also awarded the 1911 Nobel Prize in Chemistry specifically for the discovery of radium, becoming the first person to be awarded two Nobel Prizes. (Pierre had died in 1906 and Nobels are not awarded posthumously.)

Francium, element 87, was discovered by French physicist Marguerite Perey in 1939. In 1946 she named the element after her native land. That same year the name of the element made its first appearance in English, in the December issue of the Journal of the Proceedings of the Royal Institute of Chemistry:

For element 87, [...] the name Francium (Fr) has been suggested.¹

There were several false claims of discovery prior to Perey’s. One of these, by a team at the Alabama Polytechnical Institute, now Auburn University, dubbed what they thought was element 85 virginium, after the home state of the team’s lead, Fred Allison.² (See also astatine.)

¹Oxford English Dictionary, francium, 2nd Edition, 1989, Oxford University Press, accessed 13 November 2009, http://dictionary.oed.com/cgi/entry/50089429.

²Oxford English Dictionary, virginium, 2nd Edition, 1989, Oxford University Press, accessed 13 November 2009, http://dictionary.oed.com/cgi/entry/50278010. 

Radon, element 86, was discovered in 1900 by German physicist Friedrich Ernst Dorn. The previous year the Curies had discovered that radium gave off a radioactive gas, and it was Dorn that identified this gas as an elemental decay product of radium. The name radon is originally German, from rad- for radium and -on, indicating that it is a noble gas, like argon or neon. The name was in English use by 1918. From the Journal of the Chemical Society of that year:

Radium emanation is given the name Radon, Ro, which at once indicates its origin and its relationship to the argon group.¹

Note that Ro is no longer used as the chemical symbol for the element. The current symbol for Radon is Rn.

Former names for the element include niton, from the Latin nitere, to shine, and emanation or radium-emanation. These names were in use into the middle of the 20th century and are occasionally found when perusing older chemical literature.

¹Oxford English Dictionary, radon, 3rd Edition, June 2008, Oxford University Press, accessed 12 November 2009, http://dictionary.oed.com/cgi/entry/50196252. 

Astatine, element 85, was first produced in 1940 by Dale Corson, Kenneth MacKenzie, and Emilio Segrè in the cyclotron at the University of California, Berkeley. Several years later, it was discovered in nature. It is named for its short half-life, as explained by Carson in the 4 January 1947 issue of Nature:

We propose to call element 85 “astatine” from the Greek αστατος, unstable. Astatine is in fact the only halogen without stable isotopes.

There were several earlier claims for discovery that were later disproven, but the names from those mistaken finds can sometimes be found in older chemical literature. One group at the Alabama Polytechnic Institute (now Auburn University) dubbed the element alabamine, and a British-Swiss team dubbed it anglo-helvetium.¹

The chemical symbol for astatine is At. (Arsenic is As.)

¹Oxford English Dictionary, astatine, 2nd Edition, 1989, Oxford University Press, accessed 11 November 2009, http://dictionary.oed.com/cgi/entry/50013636.

See polonium

See polonium