Francium

{ syn. }

In traces

Francium [ frantsiʊm ] is a radioactive chemical element with the element symbol Fr and atomic number 87, the element is a metal and is in the 7th period, s- block.

Francium has all elements up to atomic number 104, the most unstable isotopes. Even the longest-lived isotope of francium 223Fr has a half -life of only 21.8 minutes. Because of this property and the lack of an efficient nuclear reaction for the production of francium ( 223Fr occurs in 1% of the decay of 227Ac ), it can not be produced in quantity. Francium can be studied as amalgam only as a salt in dilute solutions and highly diluted.

Experiments show that Francium is a typical alkali metal and is very similar to its lighter homologue cesium. So it is positive in aqueous solution monovalent and can be similar to cesium in the form of sparingly soluble salts, eg as perchlorate, tetraphenylborate and hexachloroplatinate, failures.

History

In 1871 the existence of an element was predicted by Dmitri Ivanovich Mendeleev, which would occupy the empty place at this time in his periodic table. He described it as an alkali metal, and gave him the name eka- cesium.

Prior to the actual discovery of francium there were three misleadingly named as a discovery of this element events:

In 1925 Dmitri Dobroserdow published a theory study in which he made predictions about the atomic weight and chemical and physical properties. He named the element Russium.

A year later, in 1926, observed two English chemists, the spectral lines of the element in studies of manganese sulfate. They named the element Virginium.

1937 again went Horia Hulubei the Romanian expect to have discovered the element and gave him the name Moldavium. However, could not find confirmation in other scientists, none of these discoveries.

Only in 1939 was Marguerite Perey prove the element as an isotope 223Fr as a decay product of actinium 227Ac doubt. It was initially called actinium -K and 1946 in francium ( from the French France " France," the homeland of the discoverer ) renamed. The name was accepted in 1949 by the International Association of Chemists.

Physical Properties

The physical properties are essentially estimates, which are determined by extrapolation of the properties of the alkali metals or by modeling. They should therefore be treated with great caution. Measurements on solids are due to the small producible quantities (a few attogram, ~ 10,000 atoms) and the high radioactivity ( activity is about 2 - million -fold higher than of 238Pu: visible amounts would evaporate immediately ) usually with today's means of technology impossible.

Safety

Classifications according to the Hazardous Substances Ordinance are not available because they only include the chemical danger and play a very minor role compared to the risks based on the radioactivity. Even the latter applies only when there is a relevant matter for that amount.