History of Science
Alkali Metals

All of the alkali metals except francium had been discovered by 1860why did it take scientists nearly another 80 years to discover francium?



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Francium is a natural chemical element but the total quantity of francium in the earth crust is only approx. 30 g. Francium has ca. 40 isotopes and isomers but only two are natural: 221Fr (in the neptunium decay chain series) and 223Fr (in the actinium decay chain series). Artificially preparation of francium isotopes is also extremely difficult and expensive; and the chemistry and physics of isotopes was developed essentially after 1940. Supplementary, the most stable isotope of francium has a half life of only 21,8 minutes and is strongly radioactive; the half lives of the artificially prepared isotopes are more smaller.

This is sufficient reason to explain why francium was later discovered and why even today is only slightly studied.