Uranium ion

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

Geochemical Nature and Types of Deposits. The cmst of the earth contains approximately 2—3 ppm uranium. AlkaHc igneous rock tends to be more uraniferous than basic and ferromagnesian igneous rocks (10). Elemental uranium oxidizes readily. The solubiHty and distribution of uranium in rocks and ore deposits depend primarily on valence state. The hexavalent uranium ion is highly soluble, the tetravalent ion relatively insoluble. Uraninite, the most common mineral in uranium deposits, contains the tetravalent ion (II). 

Uranium dioxide, UQ2, can be further oxidized to give a nonstoichiometric compound U024v, where 0 < x < 0.25. See Exercise 5.77 for a description of nonstoichiometric compounds, (a) What is the average oxidation state of uranium in a compound with composition UO,j-> (b) If we assume that the uranium exists in either the +4 or the +5 oxidation state, what is the fraction of uranium ions in each ... 

In the diuranium chlorides, the formal charge of the uranium ion is +3. Thus, 6 of the 12 valence electrons are available and a triple bond can in principle be formed. U2Clg can have either an eclipsed or a staggered conformation. Preliminary calculations have indicated that the staggered conformation is about 12 kcal/mol lower in energy than the eclipsed form, so we focus our analysis on the staggered structure. 

As with the starting complex, 4 -U, the uranium ion is displaced below the plane formed by the aryloxide ligands by 0.66 A for... 

Figure 1 Absorbed dose necessary to produce a given biological effect on a given system, in the present case 50% inactivation of V79 hamster cells in exponential growth phase. The dose needed depends on the type of the particles (photons, alpha particles, or uranium ions) and on their energy. (From Ref 15.)...

A variety of ion species, from light to heavy ions, namely, from protons to uranium ions, are utilized for the ion beam applications. Wide diversity of ion species, charge state, and beam currents is required to meet the requirements for the research of the ion beam applications. Various types of ion sources [3], using different ionization methods, such as field ionization and surface ionization, have been developed to provide optimum ion beams. An ion source... 

This affirmed necessity of positioning around the cluster, U (U ) cations is a very relevant fact, especially if coupled with the result of the channeling experiment reported above, which shows a displacement of uranium ions from their equilibrium positions. The Willis clusters can then be described also as molecularities in which the electronic charge... 

Flow coulometry experiments were performed to study the reduction of U02 in nitric, perchloric, and sulfuric acid solutions [56]. The results of these studies show a single two-electron reduction wave attributed to the U02 /U + couple. The direct two-electron process is observed without evidence for the intermediate U02" " species because of the relatively long residence time of the uranium ion solution at the electrode surface in comparison to the residence time typically experienced at a dropping mercury working electrode. The implication here is that as the UO2 is produced at the electrode surface, it is immediately reduced to the ion. As the authors note a simplified equation for this process can be written, Eq. (7), but the process is more complicated. Once the U02" species is produced it experiences homogeneous reactions comprising Eqns (8) and (9) or (8) and (10) followed by chemical decomposition of UOOH+ or UO + to [49]. 

U02.25 corresponds to U4O9, which is a well-characterized oxide of uranium known at low temperature. UO2 has the fluorite structure. The unit cell is depicted in Figure 5.27(a) and contains four formula units of UO2. (There are four uranium ions contained within the cell boundaries the eight oxide ions come from (8x /8)=l at the corners ... 

Fig. 2. Oxidation-reduction potentials of uranium ions tin 1-molar hydrochloric acid)...

Tile element uranium also exhibits a formal oxidation number of (II) in a few solid compounds, semimetallic in nature, such as UO and US. No simple uranium ions of oxidation state (II) are known in solution. 

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