![]() Francium has a slightly higher ionization energy than caesium, 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from relativistic effects, and this would imply that caesium is the less electronegative of the two. Linus Pauling estimated the electronegativity of francium at 0.7 on the Pauling scale, the same as caesium the value for caesium has since been refined to 0.79, but there are no experimental data to allow a refinement of the value for francium. The density of francium is expected to be around 2.48 g/cm 3 (Mendeleev's method extrapolates 2.4 g/cm 3). ![]() ![]() ![]() The estimated boiling point of 620 ☌ (1,148 ☏) is also uncertain the estimates 598 ☌ (1,108 ☏) and 677 ☌ (1,251 ☏), as well as the extrapolation from Mendeleev's method of 640 ☌ (1,184 ☏), have also been suggested. A calculation based on the melting temperatures of binary ionic crystals gives 24.861 ± 0.517 ☌ (76.750 ± 0.931 ☏). The melting point is uncertain because of the element's extreme rarity and radioactivity a different extrapolation based on Dmitri Mendeleev's method gave 20 ± 1.5 ☌ (68.0 ± 2.7 ☏). Francium's melting point was estimated to be around 8.0 ☌ (46.4 ☏) a value of 27 ☌ (81 ☏) is also often encountered. Liquid francium-if created-should have a surface tension of 0.05092 N/m at its melting point. A heavy element with a single valence electron, it has the highest equivalent weight of any element. įrancium is an alkali metal whose chemical properties mostly resemble those of caesium. Francium-223 also has a shorter half-life than the longest-lived isotope of each synthetic element up to and including element 105, dubnium. All isotopes of francium decay into astatine, radium, or radon. The only comparable element is astatine, whose most stable natural isotope, astatine-219 (the alpha daughter of francium-223), has a half-life of 56 seconds, although synthetic astatine-210 is much longer-lived with a half-life of 8.1 hours. Characteristics įrancium is one of the most unstable of the naturally occurring elements: its longest-lived isotope, francium-223, has a half-life of only 22 minutes. The largest amount produced in the laboratory was a cluster of more than 300,000 atoms. As little as 200–500 g exists at any given time throughout the Earth's crust aside from francium-223 and francium-221, its other isotopes are entirely synthetic. Outside the laboratory, francium is extremely rare, with trace amounts found in uranium ores, where the isotope francium-223 (in the family of uranium-235) continually forms and decays. It was the last element first discovered in nature, rather than by synthesis. Before its discovery, francium was referred to as eka- caesium or ekacaesium because of its conjectured existence below caesium in the periodic table. Obtaining such a sample is highly improbable since the extreme heat of decay resulting from its short half-life would immediately vaporize any viewable quantity of the element.įrancium was discovered by Marguerite Perey in France (from which the element takes its name) in 1939. Because of the general appearance of the other elements in its periodic table column, it is presumed that francium would appear as a highly reactive metal if enough could be collected together to be viewed as a bulk solid or liquid. The electronic structure of a francium atom is 7s 1 thus, the element is classed as an alkali metal.īulk francium has never been seen. ![]() Francium's isotopes decay quickly into astatine, radium, and radon. It is the second-most electropositive element, behind only caesium, and is the second rarest naturally occurring element (after astatine). It is extremely radioactive its most stable isotope, francium-223 (originally called actinium K after the natural decay chain in which it appears), has a half-life of only 22 minutes. Francium is a chemical element with the symbol Fr and atomic number 87. ![]()
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