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Francium-223 is the most stable isotope, with a half-life of 21.8 minutes, [8] and it is highly unlikely that an isotope of francium with a longer half-life will ever be discovered or synthesized. [22] Francium-223 is a fifth product of the uranium-235 decay series as a daughter isotope of actinium-227; thorium-227 is the more common daughter. [23]
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Of elements whose most stable isotopes have been identified with certainty, francium is the most unstable. All elements with atomic number of 106 ( seaborgium ) or greater have most-stable-known isotopes shorter than that of francium, but as those elements have only a relatively small number of isotopes discovered, the possibility remains that ...
Some nonmetals (black P, S, and Se) are brittle solids at room temperature (although each of these also have malleable, pliable or ductile allotropes). From left to right in the periodic table, the nonmetals can be divided into the reactive nonmetals and the noble gases. The reactive nonmetals near the metalloids show some incipient metallic ...
The CsFr molecule is polarised as Cs + Fr −, showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium. [86] Additionally, francium superoxide (FrO 2 ) is expected to have significant covalent character, unlike the other alkali metal superoxides, because of bonding ...
While nearly all elemental metals are malleable or ductile, a few—beryllium, chromium, manganese, gallium, and bismuth—are brittle. [40] Arsenic and antimony, if admitted as metals, are brittle. Low values of the ratio of bulk elastic modulus to shear modulus ( Pugh's criterion ) are indicative of intrinsic brittleness. [ 41 ]
Astatine is a chemical element; it has symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements.
It is lustrous, malleable and ductile, and has high electrical and thermal conductivity. Like most metals it has a close-packed crystalline structure, [422] and forms a cation in aqueous solution. [423] It has some properties that are unusual for a metal; taken together, [424] these are sometimes used as a basis to classify aluminium as a ...