Transition elements vanadium

As is usual with transitional elements, vanadium possesses considerable freedom in its valencies with niobium and tantalum, however, this freedom is less marked. This can be seen in the variation of the readiness displayed by the compounds of these elements to undergo reduction ... 

Across a transition series, atomic size shrinks throngh the first two or three elements because of the increasing nuclear charge. But, from then on, size remains relatively constant because shielding by the inner d electrons counteracts the increase in eff- Thus, for example, in Period 4, the third transition element, vanadium (V ... 

Possibly because of price and performance competition from chromium, titanium, and other transition elements, only about a dozen vanadium compounds are commercially significant of these, vanadium pentoxide is dominant. 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

Vanadium is a silvery whitish-gray metal that is somewhat heavier than aluminum, but lighter than iron. It is ductile and can be worked into various shapes. It is like other transition metals in the way that some electrons from the next-to-outermost shell can bond with other elements. Vanadium forms many complicated compounds as a result of variable valences. This attribute is responsible for the four oxidation states of its ions that enable it to combine with most nonmetals and to at times even act as a nonmetal. Vanadiums melting point is 1890°C, its boiling point is 3380°C, and its density is 6.11 glam . 

Many of its compounds must be stored in a dry, oxygen-free atmosphere or in containers of inert gas. Protective clothing and goggles should be worn when handling vanadium, as well as with most of the other transition elements. 

Examples of these forms of ions are to be found in the chemistry of the transition elements and the main group elements that can exist in higher oxidation states. As may be inferred from equations (3.26) and (3.27), alkaline conditions encourage hydrolysis, so that the form an ion takes depends on the pH of the solution. Highly acid conditions tend to depress the tendency of an ion to undergo hydrolysis. Table 3.7 contains some examples of ions of different form, the form depending upon the oxidation state of the central element, vanadium. 

Hexavalent molybdenum and tungsten, pentavalent vanadium and, to a more limited extent, niobium and tantalum form a very large number of polyoxoanions ( heteropolyanions such as [PW12O40]3- and isopolyanions such as [M07O24]6-). Unlike the polyoxoanions of the post transition elements the heteropolyanions for the most part are discrete, compact species of high... 

Trivalent Compounds.—In trivalent vanadium compounds the basic character of the element is well developed, and both normal and oxy-salts of the sesquioxide V203 are well defined, e.g. vanadous sulphate, V2(S04)3, and vanadium oxymonochloride, VOC1. It has been previously mentioned that resemblances between the elements of the A and B Subdivisions of Group V. are mainly restricted to the pentavalent compounds it is of interest to note that the oxychloride has analogues in the trivalent antimony and bismuth basic chlorides, SbOCl and BiOCl. Trivalent vanadium also displays considerable analogy, however, with other trivalent transitional elements, as shown by the following —... 

Some properties of selected vanadium compounds are listed in Table 1. Vanadium, a typical transition element, displays well-characterized valence... 

Using diolefins and carefully selected Ziegler-type catalysts, it has been possible to obtain the 1,4-c/s-, the 1,4-trans-, and the 1,2-polybutadienes more than 98% pure. In the case of polyisoprene, the 3,4-structure is produced. There are thousands of patents involving every combination of pure or mixed main-group alkyls with transition-element compounds, each claiming advantages. However, compositions containing titanium, vanadium, chromium, and, in special cases, molybdenum, cobalt, rhodium, and nickel are primarily used. 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

Transition elements. Elements of the first transition series are characterized by having incompletely filled 3d orbitals in one or more of their common oxidation states. The series includes scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper, which have electronic configurations of the form (ls)2(2s)2(2p)6(3s)2(3p)6(3[Pg.41]

As a last example of a 1 1 structure derived from a cubic close-packed anion sublattice we mention that of the mineral sulvanite CU3VS4. Here, the copper atoms occupy three of the four positions of one set of tetrahedral holes, while the vanadium atom is located at one position of the other set. Thus, the anion is no longer tetrahedrally coordinated but has all four cation neighbours on the same side. In C113VS4 vanadium may be replaced by Nb and Ta and the sulphur by Se and Te (178). These compounds all are diamagnetic semiconductors containing monovalent copper and a pentavalent transition element, as does CuTaS3 (179) where Ta, however, is octahedrally coordinated. 

Many of the transition elements exhibit more than one valence state, resulting from the possible removal of successive electrons from the inner partially filled d subshell. These d electrons may be removed singly or in groups thus the various oxidation states of an element may differ by one unit or hy more than one unit. As examples, the important oxidation states of vanadium are +3, +4, and +5 those for chromium are +2, + 3, and +6 and those for manganese are +2, +3, +4, +6, and +7. Among families of transition metals, the higher valence states become the more stable near the bottom of each family for example, in the chromium group the stability of the +6 states decreases in the order ... 

Similar aspects arise for VO, except that vanadium belongs to the 3d transition element group. The electronic structure of VO is, however, similar to that of NbO and a large isotropic 53V hyperfine interaction arises from a 4s spin density of around 30%. 

Curran and Clute (1) demonstrated an in vitro increase in cholesterol synthesis in rat liver cell clusters injected with manganese. In a similar experiment, Curran (2) injected several transition elements (V, Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn) intraperitoneally into rats. After one hour the rats were sacrificed and the livers from each group were pooled and incubated with sodium acetate-l-C. Manganese and chromium were found to increase incorporation of acetate into cholesterol by 100 percent, whereas vanadium depressed cholesterol synthesis by 50 percent. 

The recent interest in five coordination1 has led to an intensive study of a number of transition-metal complexes which appear from their stoichiometry to contain a five-coordinate metal atom. Whereas most of this effort has been focused on the later transition elements, certain key complexes of titanium, vanadium,... 

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