Francium

Francium was discovered in 1939 by the French physicist Marguerite Perey, working at the Curie Institute in Paris, who found it as a decay product of actinium; it was the last element to be discovered in nature rather than synthesised. She named it after France, her homeland. Francium is an intensely radioactive alkali metal, the least stable of the first hundred-odd elements, existing in nature only in trace amounts that vanish almost as soon as they form. Because it decays within minutes, francium has no practical uses and cannot be gathered in bulk; it exists only as a handful of atoms at a time, made in accelerators and studied by physicists probing the fine structure of the atom.

Element 87 attracted several false claims before Perey's genuine discovery, including virginium, announced by American chemists in the 1930s, and moldavium and russium, claimed by other researchers, none of which survived independent verification; the pattern of premature, ultimately mistaken announcements recurred across several of the last naturally occurring elements to be pinned down, astatine and francium alike, as physicists pushed spectroscopy and radiochemistry to their practical limits. Francium is estimated to be, at any given moment, the second least abundant element in the Earth's crust after astatine, the two rarest natural elements sitting almost side by side on the periodic table.

Francium closed the era in which new elements were still being found occurring naturally; every element discovered afterwards was made in the laboratory. Perey, who had begun as Marie Curie's laboratory assistant and rose to become a distinguished scientist and the first woman elected to the French Academy of Sciences, named the element in patriotic tribute to France. So unstable is francium that no more than a few tens of grams are thought to exist in the entire crust of the Earth at any instant, and a visible sample has never been gathered.

The element has no ancient, mythological or alchemical association, being a twentieth-century discovery; its human interest lies in its discoverer's remarkable career and in its distinction as nature's final gift to the periodic table. Perey did not receive a doctorate for the very discovery that made her famous until 1946, seven years after her initial 1939 identification of francium, a delay that reflected the limited institutional recognition then available to a laboratory assistant without a formal science degree, and her election to the Academie des Sciences in 1962 came only after decades further of published research on francium's properties and on radioactivity more broadly.