The actinoids

Of the actinoids, only uranium and thorium occur naturally in significant quantities. The naturally occurring isotopes of 

The isotopes Ac and Pa can be isolated from the decay products of in pitchblende, but are better synthesized by nuclear reactions 25.3 and 25.4. 

Cm are available on a 100 g scale, and multiple neutron capture followed by P -decay yields milligram amounts of Bk, Cf, Es and Es, plus microgram amounts of Fm. Synthesis of the heaviest actinoids was detailed in Section 3.6. Box 25.3 highlights an everyday use of Am. 

Commercial smoke detectors may function using a photoelectric detector or an ionization chamber. An ionization detector consists of two plates across which a voltage (supplied by a battery) is applied (see diagram). One plate has a hole in it, and under the hole lies a small quantity (t q)ically 2 x 10 g) of an a-particle emitter with 

When smoke enters the chamber, the current changes as ions interact with the smoke particles. The sensor is equipped with an alarm which is triggered when a change in current is detected. 

With the exception of Th and U, the actinoids are manmade, produced by nuclear reactions (see Chapter 2). Radiation hazards of all but Th and U lead to technical difficulties in studying actinoid compounds, and conventional experimental techniques are not generally applicable. 

Equation 2.17 showed the syntheses of Np and Pu lengthy irradiation of Pu in a nuclear pile leads to the 

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The lanthanoids also form metal-rich carbides of stoichiometry M3C in which individual C atoms occupy at random one-third of the octahedral Cl sites in a NaCl-like structure. Several of the actinoids (e.g. Th, U, Pu) form monocarbides, MC, in which all the octahedral Cl sites in the NaCl structure are occupied and this stoichiometry is also observed for several other carbides of the early transition elements, e.g. M = Ti, Zr, Hf V, Nb, Ta Mo, W. These... 

In some versions of the periodic table, the lanthanoids begin with cerium (element 58) and the actinoids begin with thorium (element 90). 

Difficulties in separating and isolating the lanthanoids delayed their widespread use in technology. However, today they are studied intensely, because superconducting materials often contain lanthanoids (Fig. 1.64). All the actinoids are radioactive. None of the elements following plutonium occurs naturally on Earth in any significant amount. Because they can be made only in nuclear reactors or particle accelerators, they are available only in small quantities. 

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. 

The rules above gave maximum and minimum oxidation numbers, but those might not be the only oxidation numbers or even the most important oxidation numbers for an element. Elements of the last six groups of the periodic table for example may have several oxidation numbers in their compounds, most of which vary from each other in steps of 2. For example, the major oxidation states of chlorine in its compounds are -1, +1, +3, +5, and +7. The transition metals have oxidation numbers that may vary from each other in steps of 1. The inner transition elements mostly form oxidation states of + 3, but the first part of the actinoid series acts more like transition elements and the elements have... 

The last chapter in the book treats the actinoid elements. The chemistry of Ac will be discussed there. 

Table 18.1 presents the electronic structures of the actinoids along with their major aqueous oxidation states. The structures of the M" ", and M" " ... 

Table 18.2 presents the predominant aqueous species and solid compounds of the actinoids along with their colors. Some of the AG° values are only estimates, and therefore the E-pH diagrams based upon them are subject to amendment. 

As one moves through the actinoids, the trend toward lanthanoid characteristics becomes more evident with Am as Figure 18.7 (at 10 M) illustrates. A much larger area in the figure is occupied by the An ion, but resemblance to U, Np, and Pu remains in the upper regions of the E-pH diagram. 

The members of the actinoids have a somewhat greater tendency to form complexes than those of the lanthanoids. They also show a wider variety of complexes due to their more numerous oxidation states. The cations of the actinoids display coordination numbers which are often greater than 6. Although not many data are available, M02+ and M02" " ions attach 5 or 6 HOH molecules giving the central atom a coordination number of 7 or 8, and the and ions attach 9 or 10 HOH molecules. The coordination numbers with ligands other than HOH are often of these magnitudes, but sometimes may be somewhat smaller. 

For the heavier elements of the Periodic Table, say the third transition series and the actinoids, the approximation that spin—orbit coupling is so small it can be treated as a perturbation on free-ion terms fails. Spin-orbit coupling rises rapidly with nuclear charge while interelectronic repulsion terms decrease with the diffuseness of the valence electron density of larger atoms. 

For the actinoid complexes the approximation that the ligand field splittings are small compared with the spin-orbit coupling splittings of the free-ion terms is probably not very good. A proper treatment would involve the simultaneous operation by HER, HEF and HIS on the/ configurations. 

In the actinoid elements the approximation of cubic symmetry is probably sufficient to deal with the available experimental data, with some exceptions.85 93 In the chemistry of certain of the actinoid ions the linear 0=M=0 unit can play an important role, as exemplified by the unit U02 in complexes of the uranyl type, e.g. U02(0Ac)42-. This unit introduces a very strong axial component into the ligand field which may be even more important than the cubic one.49-85 However, information on the absolute magnitudes of such components seems difficult to obtain. 

For the lanthanoid elements, ligand field splittings are so small that quenching of orbital angular momentum is not important. This probability also applies in the actinoid elements. 

There remains the possibility of g-values which depart substantially from 2.00 but are isotropic because of cubic symmetry. In practice such conditions are rare for transition metal complexes, as the Jahn-Teller theorem ensures departure from cubic symmetry in the electronic structure. However, for the lanthanoid and actinoid elements, where the spin—orbit coupling constant is very much larger than kT, the Jahn—Teller theorem may not be relevant and effective cubic symmetry certain. For the lanthanoids, g-values often depart considerably from 2.00, although some anisotropy arising from ligand field splittings is common. For the actinoids, direct observation of ESR is less common but there is evidence of a similar situation. 

The elements in a column are known as a group, and groups are numbered from 1 to 18. Older numbering styles used roman numerals and letters. A row of the periodic table is known as a period, and periods of the known elements are numbered from 1 to 7. The lanthanoids are all in period 6, and the actinoids are all in period 7. 

The analytical chemistry of the transition elements see Transition Metals), that is, those with partly filled shells of d (see (f Configuration) or f electrons see f-Block Metals), should include that of the first transition period (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and that of the second transition series (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, and Ag). The third transition series embraces Hf, Ta, W, Re, Os, Ir, Pt, and An, and although it formally begins with lanthanum, for historical reasons this element is usually included with the lanthanoids (rare-earth elements) see Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry Rare Earth Elements). The actinoid elements see Actinides Inorganic Coordination Chemistry) are all radioactive see Radioactive Decay) and those with atomic number see Atomic Number) greater than uranium (Z = 92) are artificial the analytical chemistry of these elements is too specialized to consider here. 

Figure 10 Bond distance versus force constant data for intra-row bonding in all rows (n = 1-6) of the periodic table preceding the actinoids. The solid lines show the hts to an exponential decay function (see text)...

Figure 11 Bond distance versus force constant data for interrow bonding (a) for hydrogen (n = 1) bonding to all rows (n = 1 -6) of the periodic table preceding the actinoids and (b) for second-row elements (n = 2) bonding to all subsequent rows (n = 3-6) of the periodic table preceding the actinoids. The solid lines show the fits to the exponential decay function that we have proposed. The dashed lines in (b) are the fits to the intra-row bonding shown in Figure 10...

Americium is called an actinoid or transuranium element. It occurs in Row 7 of the periodic table, a chart that shows how the chemical elements are related to each other. The actinoids are named after element 89, actinium. The term transuranium means beyond uranium in the periodic table. Uranium has an atomic number of 92. Any element with an atomic number larger than 92, therefore, is called a transuranium element. 

Protactinium belongs in the actinoids series in the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. 

Thorium is a member of the actinoid family. The actinoid elements are located in Row 7 of the periodic table. They have atomic numbers between 89 and 103. The periodic table is a chart that shows how chemical elements are related to one another. The actinoid series is named for element 89, actinium, the first element in the actinoid family. 

Among the actinoid metals, Am, Cf, and Es have properties sufficiently similar to the volatile lanthanoids that they can be prepared according to reaction (d) . Substitution of less volatile Th for La allows this method to be used for the reduction of Ac, Pu, and Cm. 

The actinoid can thus be reduced with hydrogen to form an alloy. In a subsequent step the actinoid metal is purified from the alloy by fractional sublimation ... 

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