Thorium chemical properties

The same chemical separation research was done on thorium ores, leading to the discovery of a completely different set of radioactivities. Although the chemists made fundamental distinctions among the radioactivities based on chemical properties, it was often simpler to distinguish the radiation by the rate at which the radioactivity decayed. For uranium and thorium the level of radioactivity was independent of time. For most of the radioactivities separated from these elements, however, the activity showed an observable decrease with time and it was found that the rate of decrease was characteristic of each radioactive species. Each species had a unique half-life, ie, the time during which the activity was reduced to half of its initial value. 

By this time, the Periodic Table of elements was well developed, although it was considered a function of the atomic mass rather than atomic number. Before the discovery of radioactivity, it had been estabUshed that each natural element had a unique mass thus it was assumed that each element was made up of only one type of atom. Some of the radioactivities found in both the uranium and thorium decays had similar chemical properties, but because these had different half-Hves it was assumed that there were different elements. It became clear, however, that if all the different radioactivities from uranium and thorium were separate elements, there would be too many to fit into the Periodic Table. 

The four isotopes, as those of any element, have the same chemical properties. The four are not, however, uniformly distributed in the earth s crust the occurrence of three of them, in minerals and rocks, is associated with the radioactive decay of isotopes of thorium and uranium. In most minerals and rocks the relative amounts (or the isotopic ratios) of the isotopes of lead (often expressed relative to the amount of stable lead-204) are generally within well-known ranges, which are independent of the composition of the mineral or rock they are, however, directly related to the amounts of radioactive thorium and uranium isotope impurities in them. 

Following the characterization of U(COT)2, the analogous thorium complex was synthesized 12). Its physical and chemical properties were so different from those of the uranium compound that initially there was question as to whether the complex had the same -sandwich structure. The X-ray structure anal5 is however showed it to be isostructural with U(COT)2 11). Subsequently, Pu(COT)2 13), Np(COT) 13), and Pa(COT)2 14, 15) have been prepared and their X-ray powder patterns show them all to be isostructural with U(COT)2. 

The physical and chemical properties of elemental thorium and a few representative water soluble and insoluble thorium compounds are presented in Table 3-2. Water soluble thorium compounds include the chloride, fluoride, nitrate, and sulfate salts (Weast 1983). These compounds dissolve fairly readily in water. Soluble thorium compounds, as a class, have greater bioavailability than the insoluble thorium compounds. Water insoluble thorium compounds include the dioxide, carbonate, hydroxide, oxalate, and phosphate salts. Thorium carbonate is soluble in concentrated sodium carbonate (Weast 1983). Thorium metal and several of its compounds are commercially available. No general specifications for commercially prepared thorium metal or compounds have been established. Manufacturers prepare thorium products according to contractual specifications (Hedrick 1985). 

TABLE 3-2. Physical and Chemical Properties of Thorium and Compounds... 

Physical and Chemical Properties. Some of the physical and chemical properties (i.e., K°w K°<= and Henry s law constant) that are often used in the estimation of environmental fate of organic compounds are not useful or relevant for most inorganic compounds including thorium and its compounds. Relevant data concerning the physical and chemical properties, such as solubility, stability, and oxidation-reduction potential of thorium salts and complexes have been located in the existing literature. 

California and Dr. George Angleton, Collaborative Radiology Health Laboratory, Colorado State University. These experts collectively have knowledge of thorium s physical and chemical properties, toxicokinetics, key health end points, mechanisms of action, human and animal exposure, and quantification of risk to humans. All reviewers were selected in conformity with the conditions for peer review specified in the Section 104(i)(13) of the Comprehensive Environmental Response, Compensation, and Liability Act as amended. 

In spite of considerable similarities between the chemical properties of lanthanides and actinides, the trivalent oxidation state is not stable for the early members of the actinide series. Due to larger ionic radii and the presence of shielding electrons, the 5f electrons of actinides are subjected to a weaker attraction from the nuclear charge than the corresponding 4f electrons of lanthanides. The greater stability of tetrapositive ions of actinides such as Th and Pu is attributed to the smaller values of fourth ionization potential for 5f electrons compared to 4f electrons of lanthanides, an effect that has been observed in aqueous solution of Th and Ce (2). Thus, thorium... 

Diffusion experiments in solution show that uranium Xj is tetra-valent. It is isotopic with thorium and ionium, and therefore has the same chemical properties. 

Also shown in this version of the Periodic Table is the atomic number of each element, which corresponds to the total number of electrons, and the atomic weight relative to the mass of which has been assigned a mass of 12.000 (the atomic weight of carbon shown in the Periodic Table is slightly higher than this because of the additional presence of a small amount of the isotope in natural carbon). The atomic weight represents the sum of the numbers of protons and neutrons in the nucleus of the atom. It has long been known that the elements in a vertical column have similar chemical properties because they have the same nornber of valence electrons. However, the lanthanides and actinides (except for thorium) Ihown at the bottom of the Table do not fit readily into this scheme because of the effect of/orbitals in the outer electron shells. 

Thorium (Th, at. mass 232.04) occurs in solutions exclusively in the IV oxidation state. In its chemical properties it resembles Zr and Ti, as well as the rare-earth elements. In aqueous solutions at pH < 1, it exists as colourless Th ions. It is less readily hydrolysed than Ti or Zr. The hydroxide Th(OH)4 (precipitating at pH 3.5-4) has no amphoteric properties. Thorium forms stable complexes with tartrate, citrate, and EDTA and less stable complexes with sulphate, nitrate and carbonate. 

The relationship between the members of these series may be better understood by studying a few members of one of the series. Uranium, the parent substance of its series, has an atomic weight 238, but its atoms are not permanently stable. In any second of time one atom out of each 10w explodes and emits an alpha particle which is a charged helium atom, The residue accordingly has an atomic weight 234, and its properties show that it is a different element. This substance is called uranium Xi, and its chemical properties are identical with those of thorium, from which it differs in mass alone,... 

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. 

Chapters S, 6, and 7 take up uranium, thorium, and zirconium in that order. Each chapter discusses the physical and chemical properties of the element and its compounds, its natural occurrence, and the processes used to extract the element from its ores, purify it, and convert it to the forms most useful in nuclear technology. 

Physical and Chemical Properties The second actinide element thorium, atomic number 90, has an atomic mass of... 

The chemical properties of thorium resemble those of the rare earth elements. Thorium oxides are insoluble in water and alkalis, but dissolve in acids. Th forms stable complexes with fluoride and carboxy groups. In body fluids, complexes with citrate, glutamate and transferring are formed. 

Bear, J., McTaggart, F. K., The sulphides, selenides, and tellurides of titanium, zirconium, hafnium, and thorium. II. Chemical properties,... 

The radioactive elements were called radioelements. Lacking names for these radioelements, letters such as X, Y, Z, A, B, etc., were added to the symbol for the primary (i.e. parent) element. Thus, UX was produced from the radioactive decay of uranium, ThX from that of thorium, etc. These new radioelements (UX, ThX, etc.) had chemical properties that were different from the original elements, and could be separated from them through chemical processes such as precipitation, volatilization, electrolytic deposition, etc. The radioactive daughter elements decayed further to form still other elements, symbolized as UY, ThA, etc. A typical decay chain could be written Ra - Rn RaA - RaB - , etc. Fig. 1.2. 

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