Eka-actinium

Beyond element 121, eka-actinium, a series of 6f elements may occur, in analogy to the 5/ actinidc elements following actinium. But the 5g orbital -the first g orbital at all - may be filled in competition. Consequently, a series of 32 superactinide elements [20] may exist in which inner electron shells are filled whereas the configuration of the valence electrons remains unchanged. The chemistry of such elements [14,15] would be most exciting. 

Eka-actinium (E121) —- when is the Breit term important ... 

Eliav, E., Shmulyian, S., Kaldor, U., Ishikawa, Y. Transition energies of lanthanum, actinium, and eka-actinium (element 121). J. Chem. Phys. 109, 3954 (1998)... 

The next element, number 121, might be termed eka-actinium, or perhaps superactinium (because it is followed by 32 rather than 14 inner transition elements), and the following superactinide elements (numbers 122-153, inclusive) might have chemical properties somewhat similar to, but also different from, the actinide elements. 

Transition energies in eka-actinium and its ions are collected in Table 2.3. The higher nuclear charge leads to larger relativistic effects than in actinium. The most striking... 

The element "eka-cesium" had long been suspected. Was detected as a short-lived intermediate product in the decay series of actinium. 

Thus it is evident that there are three natural radioactive isotopes of thallium, seven of lead, four of bismuth, seven elements in the polonium pleiad, three inert radioactive gases, four isotopes of radium, two of actinium, six of thorium, three eka-tantalums, and three uraniums. 

The properties of this new element left no doubt that it was the missing alkali, eka-cesium, number 87. In 1946 Mile. Perey suggested that the name actinium K be kept for the naturally occurring isotope which resulted from the decay of actinium, but that element 87 in general... 

The element francium is named for the country of France and its most stable isotope is known as actinium K. Dimitri Mendeleev assigned it the name eka-cesium prior to its actual discovery, although at this time it was also known as russium, virginium, and moldavium. Marguerite Perey, a one-time assistant of Marie Curie, discovered francium in 1939. It is not found in its elemental state and less than one ounce is thought to exist in Earth s crust at any one time. 

Uranium Y is isotopic with uranium X, and is therefore tetravalent. Since it gi es off -rays, it is unlikely, according to the Group-displacement Law, that it will change directly into trivalent actinium there should be an intermediate a-ray product. This conclusion was cozi-firmed by the discovery of eka-tantalum or protoactiniuni, which is the immediate parent of actinium. ... 

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. 

All these new discoveries, of course, verified Seaborg s theory, and the transuranium elements, along with thorium, protactinium and uranium, are now called the actinide elements. They all fit in the Periodic Table between actinium and the element eka-hafnium. Eka-hafnium is the tentative name given to the undiscovered element with the atomic number 104 which lies directly below hafnium in the Periodic Table and which is expected to have chemical properties similar to those of hafnium. 

The immediate parent of actinium is protactinium or eka-tantalum, discovered independently by Hahn and by Soddy in 1917 it occupies the position between thorium and uranium left vacant by Mendel eff in his Periodic Table of 1869. loses an a-particle yielding actinium. At one time the actinium series was regarded as a branch of the uranium series. In old minerals the... 

Now let us turn back to the last decades of the 19th century. When Mendeleev developed the periodic system of elements it contained many empty slots corresponding to unknown elements between bismuth and uranium. These empty slots were rapidly filled after the discovery of radioactivity. Polonium, radium, radon, actinium, and finally protactinium took their places between uranium and thorium. Only eka-iodine and eka-cesium were late. This fact, however, did not particularly trouble scientists. These unknown elements had to be radioactive since there was not even a hint of doubt that radioactivity was the common feature of elements heavier than bismuth. Therefore, sooner or later radiometric methods would demonstrate the existence of elements 85 and 87. 

In 1913 the British scientist A. Cranston worked with the radioelement MsTh-II (an isotope of actinium-228). This isotope emits beta particles and converts into thorium-228. But Cranston thought that he detected a very weak alpha decay, too. If that was true the product of the decay had to be the long-expected eka-cesium. Indeed, the process is described by... 

But when Segre and his coworkers were preparing for irradiating a bismuth target with alpha particles the scientific community had known about the discovery of eka-cesium for more than a year. Transactions of the Paris Academy of Sciences published a paper headed Element 87 AcK formed from actinium and dated January 9, 1939. Its author was M. Perey, the assistant of the eminent radiochemist Debierne who had announced his discovery of actinium forty years earlier. 

Table 5.5 lists all of Mendeleev s firm predictions. It contains only the elements to which he gave provisional names. Thus, it does not include elements such as astatine and actinium, which he predicted successfully but did not name. Neither does it include predictions that were represented just by dashes in Mendeleev s periodic systems. Among some other failures, not included in the table, is an inert gas element between barium and tantalum, which would have been called eka-xenon, although Mendeleev did not refer to it as such. 

There were many chemical attempts to isolate the heaviest alkali metal, which was referred to by the Mendeleevian term eka-cesium for many years. It was found using radiochemical techniques by Marguerite Perey of France in 1939. Working at the Curie Institute in Paris, she found that about 1% of actinium-227 decays via alpha emission, as shown in Equation (12.4), to produce what she named francium, after her homeland ... 

Actinium is the first element of the actinide group. This element and its lighter homologue La have ndi/iin + 1) D /2 ground states, with n = 5 in La and 6 in Ac. The heavy eka-Ac (element 121) has been predicted [16] to have an 85 8p Pi/2 ground state, due to the sizable relativistic stabilization of the 8pi/2 electron. These three atoms were the subject of an early application of our RFSCC approach [16]. 

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