The Chemistry of the Actinide and Transactinide Elements

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Additional details and discussions about the discovery of this element and the scientists involved are given in several references Thompson. First, a Transfermium Working Group decided the priority of discoveries. The names for the elements mendelevium, nobelium, and lawrencium were retained as originally proposed at the time of their discoveries.

General Properties and Reactions of The Actinides

This chapter gives a brief summary of the reported discoveries, confirmation, and nuclear properties of the claimed and confirmed transactinide elements through the year However, the primary emphasis is on the chemical properties — experimental, theoretical, and predicted — of the transactinides and a comparison of measured properties with theoretical predictions. The experimental studies of chemical properties are especially challenging because of the low production rates and the short half-lives and the need for very special facilities and the use of atom-at-a-time chemistry.

The discovery of a new element must furnish evidence that its atomic number is different from those of all the currently known elements and first claims to discovery often lacked such. As a result, there were uncertainties and controversies over priority of discovery, nuclear and chemical properties, and assignment of names. This chapter is intended to provide a unified view of selected aspects of the physical, chemical, and biological properties of the actinide elements, their typical compounds, and their ions in aqueous solutions.

The f—block elements have many unique features, and a comparison of similar species of the lanthanide and actinide transition series provides valuable insights into the properties of both. Comparative data are presented on the electronic configurations, oxidation states, oxidation—reduction redox potentials, thermochemical data, crystal structures, and ionic radii of the actinide elements, together with important topics related to their environmental properties and toxicology.

Many of the topics in this chapter, and some that are not discussed here, are the subjects of subsequent chapters of this work, which should be consulted for more comprehensive treatments. This chapter provides an opportunity to discuss the biological and environmental aspects of the actinide elements, subjects that were barely mentioned in the first edition of this work and discussed only briefly in the second edition, but have assumed great importance in recent years. This chapter also provides a summary of the chemical properties of the transactinide elements that have been characterized.

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This chapter reviews the spectra and the deduced electronic properties of isolated actinide atoms and ions observed in the vapor phase at low density. The free atoms or ions have all or most of the valence electrons present, and the observed spectra can be assigned to transitions due essentially to changes in the quantum numbers of the valence electrons.

This is in contrast to the spectra of actinides in crystals or in solution dealt with in depth in Chapter 18 , where the observed spectra are largely due to transitions within the 5f shell. In crystals, the actinide ions are exposed to the electric field of the surrounding ions, which produces a Stark effect on the levels.

The magnitude of the effect is relatively small because the 5f electrons are shielded from the crystal field by the 6s and 6p electrons. The result is a small perturbation in which each 5f level is split into a number of close components. In free atoms, the valence electrons interact strongly with the 5f electrons and also with each other.

Hence each 5f level gives rise to many daughter levels that are more widely split than the parent separations and have large angular momentum contributions from the parent.

General Properties and Reactions of The Actinides

The result in this case is a great number of levels whose structure is not simply related to the structure of the 5f levels or to the structure of the valence-electron levels by themselves. It is evident that the 5f level structure can be obtained more directly from crystal spectra but the properties of the valence electrons in particular, implications for the chemical properties must be deduced from the free-atom spectra. In this chapter, we will present an overview of the theoretical and computational developments that have increased our understanding of the electronic structure of actinide—containing molecules and ions.

The application of modern electronic structure methodologies to actinide systems remains one of the great challenges in quantum chemistry; indeed, as will be discussed below, there is no other portion of the periodic table that leads to the confluence of complexity with respect to the calculation of ground— and excited—state energies, bonding descriptions, and molecular properties. But there is also no place in the periodic table in which effective computational modeling of electronic structure can be more useful. The difficulties in creating, isolating, and handling many of the actinide elements provide an opportunity for computational chemistry to be an unusually important partner in developing the chemistry of these elements.

Much of our knowledge of the electronic properties of actinides in solutions and solids is obtained from optical spectroscopy. One of the features that sets actinide spectra apart from those of other elements in the periodic table, aside from the lanthanide series, is that their f-orbitals can be considered both as containing optically active electrons and as belonging to the core of inner shells. As a result of this dominant characteristic, the spectra of these elements, particularly of the lower valence states, are moderately insensitive to changes in the ionic environment.

6th International Conference on the Chemistry and Physics of the Transactinide Elements (TAN19)

Although ion—ligand interactions shift and split the energy levels of the f-orbitals, the scale of this crystal—field splitting is generally smaller than the intra-ionic Coulomb interaction and spin—orbit coupling. The relative insensitivity of these f-electrons to external forces also means that for these elements there is a close connection between energy levels in compounds and those in gaseous free atoms and ions. Table The necessity of obtaining accurate thermodynamic quantities for the actinide elements and their compounds was recognized at the outset of the Manhattan Project, when a dedicated team of scientists and engineers initiated the program to exploit nuclear energy for military purposes.

Since the end of World War II, both fundamental and applied objectives have motivated a great deal of further study of actinide thermodynamics. This chapter brings together many research papers and critical reviews on this subject. It also seeks to assess, to systematize, and to predict important properties of the actinide elements, ions, and compounds, especially for species in which there is significant interest and for which there is an experimental basis for the prediction.

The magnetic properties of actinide ions and compounds arise from the spin and orbital angular momenta of the unpaired electrons. The theoretical basis for understanding these properties was provided by Van Vleck in in his classic work. In this chapter, the properties of actinides in the metallic state will be reviewed with an emphasis on those properties which are unique or predominantly found in the metallic solid state.

Such properties include magnetism, superconductivity, enhanced mass, spin and charge-density waves, as well as quantum critical points. An introduction to fundamental condensed matter principles is included to focus the discussion on the properties in the metallic state. Systematics of the actinide 5f electronic structure will be presented for elements, alloys, metallic, and semi-metallic compounds so as to elucidate the unique characteristics that arise from the properties of actinides and 5f electrons in a periodic potential.

This chapter focuses on the solid state structural chemistry of actinide materials as determined by single—crystal X—ray diffraction, single—crystal neutron diffraction, powder X—ray diffraction, and powder neutron diffraction techniques. Some of the most dramatic changes have been in computer technology and software, making the data collection, reduction, and refinement processes highly automated and simplified. As a consequence, X—ray diffractometers have become nearly ubiquitous in research departments globally and neutron—scattering resources have become more advanced and accessible, resulting in the elucidation and publication of a greater number of additional actinide structures since the last edition; these structures are the focus for this chapter.

The solution chemistry of the actinide elements has been explored in aqueous and organic solutions. While the relative stabilities of the actinide oxidation states and the types of complexes formed with the actinide cations in these states vary between solvents, the fundamental principles governing their redox reactions and their complexation strengths are the same regardless of the solvent.

This chapter focuses on aqueous actinide chemistry, reflecting the wide variety of studies on actinide reactions in aqueous solutions.

Transactinide element - Wikipedia

However, three factors that are important for actinides in non—aqueous solvents should be noted. First, in non—aqueous solvents, the formation of neutral cation—anion ion pairs is often dominant due to the lower as compared to water dielectric constants of the solvents. Second, non—aqueous conditions also allow the formation of complexes between actinide cations and ligands containing soft Lewis base groups, such as sulfur. Third, non—aqueous solvents are often useful for stabilizing redox—sensitive actinide complexes, as oxidation states that are unstable in aqueous solution may be stable in non—aqueous solutions Mikheev.

Both the science and technology of the actinides as we know them today owe much to separation science.

Common Properties

Conversely, the field of metal ion separations, solvent extraction, and ion exchange in particular, would not be as important as it is today were it not for the discovery and exploitation of the actinides. Indeed, the synthesis of the actinides and the elucidation of their chemical and physical features required continuous development and improvement of chemical separation techniques. Furthermore, the diverse applications of solvent extraction and ion exchange for metal ion separations as we know them today received significant impetus from Cold War tensions and the production of metric tons of plutonium and the development of nuclear power for peaceful uses.

The advent of modern organometallic chemistry has often been cited as the report of the preparation of ferrocene, Z5—C5H5 2Fe, the first metallic complex containing a p—complexed ligand Pauson, It was not long after the report of this compound that comparable analogs of the lanthanides and actinides were reported Reynolds and Wilkinson, Since that time, the organometallic chemistry of the actinides has lagged in comparable developments to the chemistry of the transition metals.

Recent years, however, have witnessed a resurgence of interest in the non-aqueous chemistry of the actinides, in part due to the availability of a much wider array of ancillary ligands capable of stabilizing new compounds and introducing new types of reactivity. Modern organoactinide chemistry is nowcharacterized by the existence not only of actinide analogs to many classes of d—transition metal complexes particularly those of Groups 3 and 4 , but increasingly common reports of compounds and types of reactions unique to the actinide series.

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Most developments in the non-aqueous chemistry of the actinides have involved the use of thorium and uranium, both due to their lower specific activity, and to the apparent chemical similarity these elements bear to Group 4 metals in organometallic transformations. During the last two decades, the chemistry of organoactinides has flourished, reaching a high level of sophistication.

The use of organoactinide complexes as stoichiometric or catalytic compounds to promote synthetically important organic transformations has matured due to their rich, complex, and uniquely informative organometallic chemistry. Compared to early or late transition metal complexes, the actinides sometimes exhibit parallel and sometimes totally different reactivities for similar processes.

In many instances the regiospecific and chemical selectivities displayed by organoactinide complexes are complementary to that observed for other transition metal complexes. Several recent review articles Edelman. All actinide isotopes are radioactive. Since the middle of the last century, new bactinide and transactinide isotopes have been artificially produced and the use of several of the naturally occurring actinide isotopes has increased.

This production is due to the nuclear power industry and the military fabrication and use of nuclear weapons. These activities have created anxiety about the introduction of actinide elements into the environment. Consequently, environmental systems that contain or are exploited for natural actinides, or, are potentially contaminated by anthropogenic actinides, must be investigated.

The analytical techniques introduced in this chapter are used, after sampling when required, to identify and quantify the actinide isotopes and to determine the species in which they are present. The recent availability of synchrotron radiation has revolutionized actinide chemistry. This is particularly true in environmental studies, where heterogeneous samples add to the already multifaceted chemistry exhibited by these ions. Environmental samples are often inhomogeneous, chemically diverse, and amorphous or poorly crystalline. Even surrogates prepared in the laboratory to simplify the natural complexity are plagued by multiple oxidation state and varied coordination polyhedra that are a reflection of inherent 5f chemistry.

For example, plutonium can be found as Pu. In addition, dissolved actinides have significant affinities for various mineral surfaces, to which they can adsorb with or without concomitant reduction—oxidation redox activity, depending on details of the solution and surface conditions.

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The need to address topics of handling, storage, and disposal of plutonium and uranium is driven by concern about hazards posed by the element and by the worldwide quantity of civilian and military materials. The projected inventory of separated civilian plutonium for use in fabricating mixed-oxide MOX reactor fuel during initial decades of this century is constant at about metric tons and a comparable amount of excess military plutonium is anticipated from reductions in nuclear weapon stockpiles IAEA Report, Although inventories of civilian material are in oxide form, Pu from weapons programs exists primarily as metal.

Plutonium is a radiological toxin Voelz, ; its management in a safe and secure manner is essential for protecting workers, the public, and the environment. Actinide elements are ubiquitous in nature.

The Chemistry of the Actinide and Transactinide Elements The Chemistry of the Actinide and Transactinide Elements
The Chemistry of the Actinide and Transactinide Elements The Chemistry of the Actinide and Transactinide Elements
The Chemistry of the Actinide and Transactinide Elements The Chemistry of the Actinide and Transactinide Elements
The Chemistry of the Actinide and Transactinide Elements The Chemistry of the Actinide and Transactinide Elements
The Chemistry of the Actinide and Transactinide Elements The Chemistry of the Actinide and Transactinide Elements
The Chemistry of the Actinide and Transactinide Elements The Chemistry of the Actinide and Transactinide Elements

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