Period 7 element elements of the 7th period. Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K. It is one of the two least electronegative elements, the other being caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron. Francium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. It was the last element discovered in nature, rather than by synthesis. Outside the laboratory, francium is extremely rare, with trace amounts
Ida Noddack a predetermined result. According to Kenna and Kuroda technetium content expected in a typical pitchblende (50% uranium) is about 10 g/kg of ore. F. Habashi pointed out that uranium was never more than about 5% in Noddacks' columbite samples, and the amount of element 43 could not exceed 3 × 10 µg/kg of ore. Such a low quantity could not be weighed, nor give X-ray lines of element 43 clearly distinguishable from the background noise. The only way to detect its presence was to carry out radioactive measurements, a technique the Noddacks were not able to employ, but Segrè and