Actinium and the actinides

There is only one single direct NMR observation of an actinide nucleus, viz., in neat UF at 380 K and 4 bar. The measured resonance frequency is 9.2098(40) MHz, the magnetogyric ratio for this spin-7/2 nucleus y = 492.6(2)rads- G , the linewidth Wi 2 20kHz. 2 has a large Q of 

1 X 10 m which renders its direct observation extremely difficult. Indirect observation on has been extracted from H, B, C, N, 0, F, Al, P, Cu, ° Rh, Sn, and I NMR and has recently been surveyed by Kannellakopulos. Glebov has analyzed H and 0 relaxation by NpO and PuOl with respect to the electronic structure of these ions. Seppelt and Bartlett observed an unstructured, broad (lFi/2 = 550Hz) resonance for F in UFg (96% enriched, 

The Ti- F coupling (33 Hz) has been estimated from the linewidth of the unresolved F resonance in [TiFg] , confirmed recently by the direct observation of well-resolved Ti and Ti septets (7=34.0 Hz). Tarasov and Buslaev obser- 

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Fig. 5a. Standard (or formal) reduction potentials of actinium and the actinide ions in acidic (pH 0) and basic (pH 14) aqueous solutions (values are in volts...

Related topics Actinium and the actinides (12) Origin and abundance of the elements (J1)... 

Actinium and the actinide elements (thorium, etc.) also are listed separately at the bottom. Each actinide element is somewhat similar to actinium and to the lanthanide element with which it is paired. The discovery of hafnium (Hf) in 1923 and rhenium (Re) in 1925 completed the Periodic Table through uranium except for four blank spaces. 

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

All nuclides with Z > 83 are unstable. Thus, the largest members of main groups 1A(1) through 8A(18), actinium and the actinides (Z = 89-103), and the other elements of the fourth (6d) transition series (Z = 104-112), are radioactive and (as discussed below) undergo a decay. 

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. 

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 additional electrons required by the next fourteen heavier elements are to be found in the inner, 5f orbit in most cases. By the time we come to the seventh element beyond actinium, which is element 96,7 electrons have been added to this orbit when we come to the fourteenth element, the undiscovered element 103, the 5f orbit has its full complement of 14 electrons and the actinide series of elements is completed. 

Periodic table of the elements. The lanthanide series ( rare earths ), beginning with lanthanum (57), and the actinide series, which begins with actinium (89) and includes thorium (90) and uranium (92), are chemically similar. Other families of elements read vertically down the table—at the far right, for example, the noble gases helium, neon, argon, krypton, xenon, radon. 

Americium and curium were placed after actinium in the actinide series in the Periodic Table because their chemical properties were similar. Since that time, elements with atomic numbers to 118 have been reported by scientists around the world. 

The elements from actinium onwards (the actinides and transactinides) can also be considered as transition elements. 

The kind of analysis outlined above can yield accurate assessments of the extent to which f electrons participate in the chemical bonding in the lighter actinides, but they are dependent upon accurate experimental data for actinium and the transplutonium elements. Both thermochemical and optical spectroscopic data are also useful for analysis of the factors determining the oxidation states of the actinide atom in compounds (Johansson 1977a, Brooks et al. 1984). For example, the stability of 450 different halides and oxides of the lanthanides were investigated, and the existence or non-existence of di-, tri- and tetravalent compounds was accounted for very well (Johansson 1977a). 

Inner transition metals The final electrons of the iimer transition metals enter an f sublevel. The inner transition metals are placed below the main body of the periodic table. They include the lanthanide series, which are in period 6 and follow the element lanthanum, and the actinide series, which are in period 7 and follow actinium. The lanthanides have very similar properties and are silvery metals with relatively high melting points. They are used in welder s glasses, television screens, and lasers. The actinides are all radioactive, and most are synthetic elements. They include the transuranium elements, which are elements that have an atomic number greater than 92. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

URANIUM compounds), Pb from the thorium series, and Pb from the actinium series (see Actinides and transactinides). The crystal stmcture of lead is face-centered cubic the length of the edge of the cell is 0.49389 nm the number of atoms per unit cell is four. Other properties are Hsted in Table 1. 

The actinides ( actinons or actinoids ) are the fourteen elements from thorium to lawren-cium inclusive, which follow actinium in the periodic table. They are analogous to the lanthanides and result from the filling of the 5f orbitals, as the lanthanides result from the filling of the 4f. The position of actinium, like that of lanthanum, is somewhat equivocal and, although not itself an actinide, it is often included with them for comparative purposes. 

The actinoid elements (or actinides An) constitute a series of 14 elements which are formed by the progressive filling of the 5/ electron shell and follow actinium in the periodic table (atomic numbers 90-103). All of the isotopes of the actinide elements are radioactive and only four of the primordial isotopes, Th, and " " Pu, have a sufficient long half-life for there to be any of these left in nature. 

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