Francium ions

Taking francium as an example, it was assumed that the minute traces of francium ion Fr could be separated from other ions in solution by co-precipitation with insoluble caesium chlorate (VII) (perchlorate) because francium lies next to caesium in Group lA. This assumption proved to be correct and francium was separated by this method. Similarly, separation of astatine as the astatide ion At was achieved by co-precipitation on silver iodide because silver astatide AgAt was also expected to be insoluble. 

It is thought that the degree of association between the rubidium, cesium or francium ions and the hydroxide ion is such that they would always be fully dissociated. This may be partly because that any association that did occur would be difficult to detect experimentally. Undoubtedly, due to their larger ionic size, it would be expected that the association between these ions and the hydroxide ion would be... 

All of these elements have only one electron in their outer energy shells.. Even francium, with 87 electrons, has only one in the outer shell. The other 86 are in inner shells. It is easy for the alkali metals to lose that one electron, as hydrogen does, and become positively charged ions. 

All of the alkali metals are electropositive and have an oxidation state of 1 and form cations (positively charged ions) by either giving up or sharing their single valence electron. The other elements of group 1 are lithium (jLi), sodium (jjNa), potassium (j K), rubidium (j Rb), cesium (jjCs), and francium (g Fr). Following are some characteristics of the group 1 alkali metals ... 

Francium has many more isotopes (33) than compounds. However, knowing how the other alkali metals form compounds, one may speculate on several possibilities. Its metal ion most likely is Fr, which means it has a very low level of electronegativity and would combine vigorously with anions of nonmetals that have a very high electronegativity. For example, if it reacted with chlorine, it would form FrCl and if a chunk of metallic francium (which would be hard to find) were dropped in water, it would explode and form francium hydroxide (2Fr + 2Up 2FrOH + H t). 

The heavy isotopes or francium can be formed by irradiation of uranium or thorium by protons of high energy the lighter isotopes can be obtained by nuclear reactions induced in gold, tellurium, or lead targets by heavy ions. 

The element francium is formed in the natural radioactive decay series and in nuclear reactions. All its isotopes are radioactive with short half-lives. The ion behaves as would be expected from its position in the group. 

The Group 1 elements—lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr)—are called the alkali metals. The alkali elements are soft, silvery-white metals and good conductors of heat and electricity. Their chemistry is relatively uncomplicated they lose their s valence electron and form a 1 + ion with the stable electron configuration of the noble gas in the preceding period. 

The Group lA elements (Li, Na, K, Rb, Gs, and Fr) are called the alkali metals. The name alkali derives from an old word meaning ashes of burned plants. All the alkali metals are soft enough to be cut with a knife. None are found in nature as free elements, because all combine rapidly and completely with virtually all the nonmetals and, as illustrated in Figure 3.14, with water. These elements form positive ions (cations) with a +1 charge. Francium, the last member of Group lA, is found only in trace amounts in nature, and all its 21 isotopes are naturally radioactive. 

The most significant chemical property of most members of the chains is that each element is carrier-free — there are no inactive atoms to compete with the radioactive ones for chemical sites, such as ion-exchange sites on the inner surface of a container. In extreme cases, such as polonium in the Th chain, there will be few if any atoms at a given time. The specific activity of Th is 4,070 Bq/g. If 1 g of thorium is in equilibrium with its chain, the activities of 0.15 s Po and 0.3 ps Po will be 4,070 Bq and 2,609 Bq (64.1%), respectively. On average there will be 881 atoms of Po present at any given time. Only 0.1% of the time is even one atom of Po present. Francium is even more rare. It occurs only in the chain (and the extinct 4n + 1), and then only in a 1.4% branch. There are only a few grams of Fr in the entire crust of the Earth. 

The chemical properties span a range similar to the representative elements in the first few rows of the periodic table. Francium and radium are certainly characteristic of alkah and alkaline earth elements. Both Fr and Ra have only one oxidation state in chemical comhina-tions and have little tendency to form complexes. Thallium in the 1+ oxidation state has alkah-like properties, but it does form complexes and has extensive chemistry in its 3+ state. Similarly, lead can have alkaline earth characteristics, hut differs from Ra in forming complexes and having a second, 4+, oxidation state. Bismuth and actinium form 3+ ions in solution and are similar to the lanthanides and heavy (Z > 94) actinides. Thorium also has a relatively simple chemistry, with similarities to zirconium and hafiuum. Protactinium is famous for difficult solution chemistry it tends to hydrolyze and deposit on surfaces unless stabilized (e.g., by > 6 M sulfuric acid). The chemistry of uranium as the uranyl ion is fairly simple, hut... 

Relativistic many-body perturbation theory has been applied to study the polarizabilities of the ions of the francium isoelectronic sequence.This approach, which adopts SOS expressions, decomposes the polarizability into an ionic core contribution, a counterterm compensating for excitations from the core to the valence shell, and a valence electron contribution. These calculations have presented benchmark results for comparison with experiment. A similar relativistic many-body perturbation theory study of the energies and oscillator strengths of the nsij2, npj, ndj, and nfj (n < 6) states of Li has been carried out and has enabled to evaluate the polarizabilities of its ground state. 

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