Isotopes of francium

ISOTOPES There are no stable isotopes of francium found on Earth. All of its 33 isotopes (ranging from Fr-201 to Fr-232) are radioactive therefore, the one with the longest half-life of about 20 minutes (Fr-223) is the one used to determine its atomic weight. Fr-223 is the only radioisotope of francium that is found naturally as a decay product from other unstable elements. 

Only about one ounce of natural francium exists in the Earths crust. All the other isotopes of francium are artificially produced in very small amounts (just a few atoms at a time) that exist for a few seconds to minutes. 

Given that all isotopes of francium are radioactive with relatively short half-lives, there are few practical uses for it—except as a source of radiation to study the radioactive decay process. 

Studies indicate that no further isotopes of francium with half-lives longer lhan those already known should exist. Thus, among the lirsl 101 elements of the periodic chan, francium is ihe mosl unstable. The shun half-lives uf the isotopes explain the difficulties in isolating and confirming the element and of leuming more of the detailed chemistry of the element. 

The vertical profile of francium (Fr), markedly different from other Group 1 elements, is based on calculation rather than direct measurement. 223Fr, the longest-lived isotope of francium and a daughter of 227Ac, is formed with a branching ratio of approximately 1.4%. With a half-life of 22 min (compared to the 22-year half-life of 221 Ac) it should exist in seawater, in minute quantities, in direct proportion to the concentration of 227Ac. 

Several other isotopes of francium are also known as products of synthesis, but most of these isotopes are of very short half life. 

Although there are a number of isotopes of francium, most decay very rapidly to other elements. Most isotopes with masses of 223 AMU and lower emit tt-particles (consisting of two protons and two neutrons) to become astatine. Some low mass francium isotopes can also undergo electron capture (the conversion of a proton to a neutron through the absorption of an electron) to become radon. Francium isotopes with masses of 220 AMU and higher can undergo /3-decay (the conversion of a neutron to a proton through the emission of an electron) to become radium. Francium-223 is the most stable isotope and has a half-life of 21.8 minutes. 

Li, Rb and Cs are of lower abundance and are obtained from silicate minerals. Francium (Fr) is a radioactive element and occurs in very small quantities in uranium minerals. The longest-lived isotope of francium is 223Fr (ty2 = 22 min). 

Francium may be the rarest element found on Earth s surface. Some experts believe that no more than 15 grams (less than an ounce) of the element exist in Earth s crust. The element was discovered in 1939 by French chemist Marguerite Perey (1909—1975). All isotopes of francium are radioactive. 

Forty-one isotopes of francium have been produced artificially. The most stable is francium-223. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element s name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope. 

The element s name comes from the country France, and it was named in 1946 by Marguerite Perey (1909-1975), who discovered the element in 1939. Element 87 was predicted in 1871 by Mendeleev. He gave it the name eka-caesium. It was known first as actinium-K as a radioactive product of the decay of actinium, and it is the most unstable of the first 101 elements. Although francium occurs naturally, its short half-life means that there are only a few grams of the element at any time in the crust of the Earth. Because the longest lasting isotope of francium lasts only 22 minutes, it has no commercial uses. 

Francium, then, does occur in nature as a result of radioactive decay, but it is indeed rare. The longest-lived isotope of francium has a half-life of only twenty-one minutes. 

Note all isotopes of francium are radioactive with very short half-lives 2g)Fr is the most common isotope it has a half-life of 21 minutes. 

The alkali metals - lithium, sodium, potassium, rubidium, caesium and francium - are members of group 1 of the periodic table, and each has a ground state valence electronic conhguration ns. Discussions of these metals usually neglect the heaviest member of the group only artihcial isotopes of francium are known, the longest lived, Fr, having... 

Francium is formed only by radioactive decay and in nuclear reactions all the isotopes of francium have short half-lives, the longest of which is 21 minutes (francium-223). The few chemical studies which have been carried out indicate that it would have similar properties to those of the other alkali metals. 

None cf the natural radioactive elements had such a short half-life, even the artificially synthesized element 85 had a half-life measured in hours. There were hopes to find other natural isotopes of francium with longer half-lives. But in fact francium-223 proved to be the only francium isotope found on Earth. 

The chemistry of lithium, rubidium, and cesium is less important all isotopes of francium, the last member of the group, are radioactive. 

The second longest-lived isotope of francium is francium-222. It decays by beta-minus emission only. Write a nuclear equation for this process. 

Suppose that a fairly stable isotope of francium has been discovered. The chemist decides to determine its atomic weight by quantitatively converting a sample of francium chloride to silver chloride. Suppose she starts with 0.00476 g of francium chloride and finishes with 0.00263 g of silver chloride. Determine the atomic weight of francium, using these data. 

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