Chemistry of Actinium

Hageman, F. The Chemistry of Actinium , in G.T. Seaboig and J.J. Katz (editors), The Actinide Elements, National Nuclear Energy Series, IV-14A, p. 14, McGraw-Hill, New York, NY, 1954. 

Since the chemistry of actinium is confined to the Ac + ion, it can readily be separated from thorium (and the lanthanides, for that matter) by processes like solvent extraction with thenoyltrifluoroacetone (TTFA) and by cation-exchange chromatography. The latter is an excellent means of purification, as the Ac + ion is much more strongly bound by the resin than its decay products. 

In 1945 Glenn Seaborg proposed that actinium was the first member of a family of fifteen elements (the actinides ), characterized by the possession of the 5/orbitals. His proposal was based on the similarity of the chemistry of actinium to that of lanthanum (atomic number 57), which is the first member of the fifteen elements of the trivalent lanthanide family. Actinium is somewhat more basic than lanthanum but, like lanthanum, forms compounds that have strongly ionic bonds. Many actinium compounds are... 

The chemistry of actinium has not been extensively studied due to its scarcity, radioactivity and the difficult nature of its decay products. Its chemistry should be very similar to that of lanthanium and therefore its white-colored sesquioxide is expected to be hexagonal (A-type see table 25) (Weigel and Hauske 1977). 

As the parent of actinium in this series it was named protoactinium, shortened in 1949 to protactinium. Because of its low natural abundance its chemistry was obscure until 1960 when A. G. Maddock and co-workers at the UK Atomic Energy Authority worked up about 130g from 60 tons of sludge which had accumulated during the extraction of uranium from UO2 ores. It is from this sample, distributed to numerous laboratories throughout the world, that the bulk of our knowledge of the element s chemistry was gleaned. 

The chemistry of neptunium (jjNp) is somewhat similar to that of uranium (gjU) and plutonium (g4Pu), which immediately precede and follow it in the actinide series on the periodic table. The discovery of neptunium provided a solution to a puzzle as to the missing decay products of the thorium decay series, in which all the elements have mass numbers evenly divisible by four the elements in the uranium series have mass numbers divisible by four with a remainder of two. The actinium series elements have mass numbers divisible by four with a remainder of three. It was not until the neptunium series was discovered that a decay series with a mass number divisible by four and a remainder of one was found. The neptunium decay series proceeds as follows, starting with the isotope plutonium-241 Pu-24l—> Am-24l Np-237 Pa-233 U-233 Th-229 Ra-225 Ac-225 Fr-221 At-217 Bi-213 Ti-209 Pb-209 Bi-209. 

The aqueous chemistry of the two rows of f-block elements, the lanthanides (lanthanum to lutetium) and the actinides (actinium to lawrencium), are sufficiently different from each other to be dealt with in separate sections. Similarities between the two sets of elements are described in the actinide section. 

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. 

A tiny amount of a very unstable species (half-life, 21 minutes) has been detected among the decay products of actinium tracer experiments by Mile. M. Perey showed that this species has the same chemistry as that of cesium and is presumably the heaviest alkali metal. It is named francium after Mile. Perey s homeland. 

Moseley then played with a problem concerning the life of an emanation of actinium, one of the radioactive elements. This period was so short that special, delicate devices had to be constructed to detect it. Together with the Polish scientist, K. Fajans, Professor of Chemistry at the University of Munich, he solved the question. The average life of the emanation was less than one five-hundredth of a second. 

The general chemistry of Ac3 in both solid compounds and solution, where known, is very similar to that of lanthanum, as would be expected from the similarity in position in the Periodic Table and in radii (Ac3, 1.10 La3, 1.06 A) together with the noble gas structure of the ion. Thus actinium is a true member of Group 3, the only difference from lanthanum being in the expected increased basicity. The increased basic character is shown by the stronger absorption of the hydrated ion on cation-exchange resins, the poorer extraction of the ion from concentrated nitric acid solutions by tributyl phosphate, and the hydrolysis of the trihalides with water vapor at 1000°C to the oxohalides AcOX the lanthanum halides are hydrolyzed to oxide by water vapor at 1000°C. 

The f-block elements comprise two series of inner transition elements which appear, firstly after lanthanum and secondly after actinium, in the Periodic Table. The elements from cerium to lutetium are known as the lanthanides and, because of its chemical similarity to these elements, lanthanum is usually included with them. Scandium and yttrium also show strong chemical similarities to the lanthanides, so that the chemistry of these elements is also often considered in conjunction with that of the lanthanide series. The second series of f-block elements, from thorium to lawrencium, is known as the actinide series and again it is usual to consider actinium together with this series. 

K. W. Bagnall, Chemistry of the Rare Radioelements (Polonium, Actinium), Butterworths, London, 1957... 

Pure and Applied Chemistry (lUPAC), the governing body that officially confirms and names any new elements. The lUPAC lists the atomic weight in brackets when an element does not have any stable nuclides. For example, the atomic weight of actinium is listed as [227]. This represents the mass of its longest-lived isotope. 

Nobelium is a member of the actinide series of elements. The ground state electron configuration is assumed to be (Rn)5fl47s2, by analogy with the equivalent lanthanide element ytterbium ([Kr]4fl46s2) there has never been enough nobelium made to experimentally verify the electronic configuration. Unlike the other actinide elements and the lanthanide elements, nobelium is most stable in solution as the dipositive cation No ". Consequently its chemistry resembles that of the much less chemically stable dipositive lanthanide cations or the common chemistry of the alkaline earth elements. When oxidized to No, nobelium follows the well-estabhshed chemistry of the stable, tripositive rare earth elements and of the other tripositive actinide elements (e.g., americium and curium), see also Actinium Berkelium Einsteinium Fermium Lawrencium Mendele-vium Neptunium Plutonium Protactinium Ruthereordium Thorium Uranium. 

Review of actinium and the actinides Comprehensive In organic Chemistry voI, 5, J. C. Bailar, Jr. etal.. Eds. (Pergamon Press, Oxford, 1973) passim. 

The actinides are a row of radioactive elements from thorium to lawrencium. They were not always separated into their own row in the periodic table. Originally, the actinides were located within the d-block following actinium. In 1944, Glenn Seaborg proposed a reorganization of the periodic chart to reflect what he knew about the chemistry of the actinide elements. He placed the actinide series elements in their own row directly below the lanthanide series. Seaborg had played a major role in the discovery of plutonium in 1941. His reorganization of the periodic table made it possible for him and his coworkers to predict the properties of possible new elements and facilitated the synthesis of nine additional transuranium elements. 

Seaborg and Katz, The Actinide Elements 1954 The Chemistry of the Actinide Elements 1957 the name stems from the hypothesis that in the periodic table they form a series beginning with actinium, like the lanthanide series of the rare earths (see p. 957). 

In 1911 the outstanding British radiochemist F. Soddy published a book entitled Chemistry of Radioactive Elements where he described actinium as an almost unknown element. He wrote that its atomic weight was unknown, the mean life-... 

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... 

Uranium differs considerably from tungsten and molybdenum in the chemistry of the lower oxidation states. Uranium (III) has great similarity to the tripositive rare-earth elements and actinium, and uranium (IV) resembles thorium and cerium (IV). Thus uranium (III) and uranium (IV) are not acidic in character they do not tend, like tungsten... 

It was a mystery that actinium exists in nature. Its most long-lived isotope, Ac, has a half-life of 22 years. It must have a long-lived precursor, from which it is continuously formed. Otto Hahn and Use Meitner, working at the Kaiser-Wilhelm Institute for Chemistry, Berlin, were aware of that and started an examination of the siliceous residues of pitchblende. While Otto Hahn was absent due to service in the army, in 1918 Lise Meitner succeeded, by utilizing tantalum pentoxide as a carrier, in detecting a long-lived alpha emitter that could be the mother of actinium. Although she had not separated the element itself, she (and Otto Hahn) had discovered the new element number 91. 

The most interesting elements of the seventh row are those following actinium. For some of these elements a large amount of chemistry is known. The first four, actinium, thorium, protactinium, and uranium, used to be shown in the periodic... 

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