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Francium
Francium is an extremely rare and highly unstable element in Group 1 and Period 7 of the Periodic Table. As a radioactive alkali metal, it was the last naturally occurring element discovered. Represented by the symbol ‘Fr’ and assigned atomic number 87, francium is a soft, low-melting, silvery-white metal. In terms of electropositivity, it is second only to cesium (Cs), and is also the second-rarest naturally occurring element, after astatine. The Earth's crust is estimated to contain no more than 15 grams of francium at any given time.
1.0Introduction
Francium is notable because it was the last element to be identified naturally; it was discovered by Marguerite Perey in 1939. It is incredibly rare, with an estimated 15 grams present in the Earth's crust at any given time. Found in trace amounts in uranium and thorium ores, francium is produced as actinium decays. Because of its radioactive nature and scarcity, francium is still one of the least understood and least common elements in nature.
2.0Physical Properties of Francium
Due to its rarity and high radioactivity, some of these values, especially the melting and boiling points, are estimates based on extrapolation from related elements like caesium.
3.0Chemical Properties of Francium
- Reactivity: Francium is highly reactive, much like other alkali metals, and would react vigorously and potentially explosively with water to form francium hydroxide (FrOH) and hydrogen gas.
- Oxidation State: Francium typically exhibits an oxidation state of +1, consistent with alkali metals.
- Compounds: Francium can form francium chloride (FrCl) and francium hydroxide (FrOH). However, knowledge about these compounds is scarce due to francium's extreme instability and brief half-life.
4.0Francium Decay
The isotopes of francium that have mass numbers between 200 and 232 decay primarily as alpha or beta particles.
Examples of the decay pathways for francium are :
- Francium-223: This isotope has the most extended half-life at 22 minutes. It can emit an alpha particle (a helium nucleus) to transform into astatine-219 or a beta particle (an electron) to become radium-223. The beta particle is released when a neutron in the nucleus converts to a proton.
- Francium-221: With a half-life of 5 minutes, this isotope can emit an alpha particle to form astatine-217 or a beta particle to change into radium-221.
- Francium-216: This isotope has a very short half-life of 0.7 microseconds. It can emit an alpha particle to produce astatine-212 or a positron to form radon-216.
- Francium-212: This isotope has a half-life of 19 minutes. It can emit an alpha particle to create astatine-208 or capture an orbital electron to produce radon-212. During this electron capture process, the nucleus captures one of the atom's electrons and emits a neutrino.
5.0Uses of Francium
- Due to its volatility and scarcity, francium has no commercial applications. It does, however, have restricted use in a few areas:
- Research: Using francium in chemical studies advances our knowledge of atomic structure and reactions.
- Spectroscopy: It is used to examine its properties in a variety of spectroscopic investigations.
- Medical Diagnostics: Research has been done on applying francium to diagnosing ailments like cancer.