Tetravalent elements

Oxygen and any other divalent elements present are ignored. Any other monovalent elements present, such as halogens, are treated as hydrogens, any other tetravalent elements (e.g. Si) as carbons. If other trivalent elements are contained in the molecules (this is rather unlikely for most organic molecules, but trivalent phosphorus is one example) they are treated as nitrogens. 

Here, other monovalent elements than hydrogen (F, Cl, Br, I) are counted as hydrogens , other trivalent elements such as phosphorus are counted as nitrogen and tetravalent elements (Si, Ge) are handled the same way as carbons. 

Gabelica, Z., and Guth, J.L (1989) Germanium-rich MFl zeolites the first example of an extended framework substitution of silicon by another tetravalent element, in Zeolites Pacts, Figures, Future, (eds P.A. Jacobs, and... 

Both the tri valent and tetravalent elements (Ce, Nd, Eu, Am and Zr, Th, Pu, respectively) have high distribution coefficients, although the values for Pu are lower than expected. 

Generally, a significantly increased distribution coefficient is obtained after a contact time of 6 months in comparison with 1 week (by a factor of less than five), especially for the tri-and tetravalent elements (and Ra) on granite. Evidently the diffusion of hydrolyzed products into the grains is a slow process. Radionuclide Species in Groundwater... 

For the tetravalent elements the maximum concentration in solution will be limited solely by the precipitation of hydroxides which might be transferred into dioxides, possibly irreversibly. Species in solution would be hydrolysis products. A large part of the soluble fraction would be non-charged or anionic ( ). 

Retention in the Hostrock. For granite, apparent surface to mass ratios of about 3 m /kg for Cs, 2 m /kg for divalent elements and <10 m /kg for tri- and tetravalent elements have been estimated, based on Kd/Ka-measurements on Cs, Sr and Am on granitic macro surfaces (1,31). Retention factors are given in Table IX, as generated from measured K.-values (from Table V), assuming long contact time, non-oxidizing conditions and representative fracture and permeability data for the rock (p. 

The latter statement refers to concurrent work by A. Bilewicz et al. [4] who studied the sorption of Zr, Hf, Th, and Rf on cobalt ferrocyanide surfaces. These ferrocyanides are known to be selective sorbents for heavy univalent cations such as Fr+, Cs+, and Rb+. However, some ferrocyanides such as Co ferrocyanide have been found to exhibit also particularly high affinities for tetravalent elements such as Zr4+, Hf4+, and Th4+ involving the formation of a new ferrocyanide phase between the 4+ cation and the Fe(CN)4 anion. 

Later, he accepted the elemental nature of the rare earths and he tried to place them in the periodic table according to a homologous accommodation methodology, as Mendeleev did. In 1876, Meyer placed cerium, erbium, and yttrium in the boron group as trivalent elements, but he placed lanthanum in the column of the tetravalent elements. 

Chemisorption is very pronouneed if the radionuelide is able to react with the surface. An example is the sorption of hydroxo complexes of tri- and tetravalent elements by the silanol groups on glass surfaces. Sorption increases with the formation of mononuclear hydroxo complexes in solution and deereases with the eondensation to polynuclear complexes at higher pH values. Several measures may be taken to suppress ion exchange or chemisorption of traces of radionuclides on glass surfaees ... 

It is thought by some that the metal acts as a tetravalent element in chromium dioxide, CrOa, but this compound may also be considered as a basic chromic chromate, CrgOg-CrOg. Chromium appears to function as a pentavalent element in the oxychloride, CrOClg, and its derivatives. The perchromic adds and perchromates have Jong been thought to contain heptavalent chromium, but it would appear that... 

Ternary and polynary oxides of trivalent to hexavalent americium are obtained by solid-state reactions of Am20s and Am02 with the oxides of various elements. Compounds of pentavalent and hexavalent americium, which are iso-structural with the corresponding ternary oxides of Pa, U, Np, and Pu, are formed only with the oxides of alkali metals and alkaline earth metals. By reaction of Am02 with oxides of tetravalent elements—e.g., SiO, ZrO, or... 

Fig. 5. Oxy-, hydroxy-, sulfato-, and hydrogen sulfato-derivatives of a trivalent element X and a tetravalent element F.

The generalized data on the stmcture chemistry of anhydrous actinide(III) and (IV) orthophosphates are presented in the literature for some actinides, for example, for transuranics [1,2], or for actinide(III) and (IV) orthophosphates of selected stmctural modifications such as monazite, zircon or NaZr2(P04)3 (NZP) types [3-6]. Some of the published reviews include wider orthophosphate families, among them the phosphates of tetravalent elements [7], of tetravalent actinides [8,9], of f(III)- and f(IV)-elements [10] as well as of the anhydrous... 

Structural chemistry of tri- and tetravalent actinide orthophosphates (and their analogues) is an important part of scientific field dealing with the influence of f-electronic shell and electronic structure of tri- and tetravalent elements upon structure formation and properties of their solid compounds. 

I.V. Tananaev (Ed.), Tetravalent Element Phosphates, Nauka, Moscow, 1972. 

Other monovalent elements (F, Cl, Br, and I) are counted as hydrogens, trivalent elements (P) are counted as nitrogen, and tetravalent elements (Si) are included with carbon. For chemically possible formulae, r+ db> — 1.5. Odd-electron ions (M+ ) will have an integer value and even-electron ions will have 0.5 r + db more than expected, so round up to next lowest integer.32,33 By way of example, Kind and Fiehn139 have described an integrated application of accurate mass data to metabolite identification, constrained by isotope abundance information and valence rules, in addition to the KI (Section 9.10.4.3.2). 

The most important representatives of tetravalent elements are titanium and zirconium because of their uses as advanced construction materials in different technologies. Systems of titanium and zirconium fluorides and chlorides with alkali metal fluorides and chlorides, respectively, can be found in the Phase Equilibria Diagrams Database (1993). A number of compounds with various stoichiometry are formed in these systems, depending on the size of the titanium and zirconium cation and the polarization ability of the alkali metal. Some of these compounds are very stable and melt congruently even at relatively high temperatures. On the other hand, some compounds melt incongruently and their existence is limited to a certain temperature range. 

Another f pe of lattice this time of the homopolar class — b>iind jii normal al< icy ini ormetallir compounds is I ho tetrahedral cubic or adamantine lattice, which, when all I In atoms are carbon atoms, occurs in the diamond, as shown in Fig. 31. This lattice is also present in crystals of the other tetravalent elements, silicon, germanium and grey tin. In all of these elements the atoms have four outer-layer or valency electrons, each of which contributes to the formation of the four tetrahedral homopolar valency... 

Zeolites and zeotypes can be defined as microporous crystalline structures (Figure 1 and Table 1) in which the framework is formed by tetrahedral of silica, in which there is isomorphic substitution with trivalent or tetravalent elements such as for instance Al, Ge, B, Fe, Cr, Ge, Ti, etc. [1]. Similar types of structure can also be achieved with the framework formed by Al and P, with or without other transition metal elements [2]. These types of structure are denoted as AlPOs, SAPOs, and MEAPOs, depending on the composition of the framework [3]. 

The author presented the thermodynamic systematics for the extraction equilibria of tetravalent elements from nitric acid solutions both by tri-n-butyl-phosphate (TBP) in kerosine and by theonyltrifluoracetone TTA in benzene. 

Tanatar (1904 3) also studied the basic acetate and concluded that its peculiar properties led to the supposition that beryllium is a tetravalent element with an atomic weight of 18.2. His belief is apparently not shared by others as the valency of... 

Repeats the work of Urbain and Dacomlie (1901 2) on the acetate and comes to the conclusion that Be is a tetravalent element with the atomic weight x8.a. 

Inorganic ion-exchangers with a layered structure, belonging to the class of acid phosphates of tetravalent elements, can exchange transition-metal ions and intercalate organic molecules between the layers to obtain complexes formed in... 

This was the theory to which Kolbe and Frankland later pointed, in support of their argument that it was they, not Kekule or Couper, who had first declared carbon a tetravalent element. 

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