Variable valency oxidation states

ChemProp Group Oxidation Number - Inert Gas Core - 8-electron configuration - V-type Diagrams - Group Oxidation State - Variable Valence. Ligands - [M(OH2)6] - Oxyanions. 

The chart of oxidation state and f-electron configuration between the actinides and the lanthanides is provided in Figure 1. The light actinides exhibit significant oxidation state variability with valences from II to VII. The boxes with question marks indicate oxidation states that have been reported in the hterature once but are questionable and have not... 

In the case of oxides with variable valence state, the degree of densification may depend further on partial oxygen pressure in the atmosphere. For instance, spinel MgCr204 requires for its densification an O2 pressure lower than 10 Pa (Anderson, 1974). Maximum densities are attained at an oxygen pressure beyond which the spinel becomes unstable and volatilizes. 

Oxidation of variable valence metal ions to higher valence state is desirable, for example, in hydrometallurgy, water conditioning, etc. The kinetics of Fe(II) and Ti(III) oxidation by oxygen in acidified water solutions was investigated. An investigation of oxidation process kinetics was carried out in the same equipment as mentioned above. It was established that... 

The transition elements are often said to exhibit variable valency. Because they so readily form complex compounds, it is better to use the term variety of oxidation states . The states usually found for the elements Sc-Zn are ... 

Transition-metal oxides are particularly effective decomposition and burning-rate catalysts. The metal elements can demonstrate variable valence or oxidation states. 

When a d-metal atom loses electrons to form a cation, it first loses its outer s-electrons. However, most transition metals form ions with different oxidation Variable valence is discussed further states, because the ( -electrons have similar energies and a variable number can be... 

The exhibition of variable valency is indeed a characteristic of transition metals. Main group metal ions such as those of groups 1 or 2 exhibit a single valence state. Other main group metals may show a number of valencies (usually two) which are related by a change in oxidation state of two units. This is typified by the occurrence of lead(iv) and lead(ii) or thallium(iii) and thallium(i). However, all the transition metals exhibit a range of valencies that is generally not limited in this manner. 

Clearly then, in glasses coloured by metal ions, the co-ordination chemistry of the transition metal ion has a major influence on the colour. The other major influence is the oxidation state of the metal ion, since variable valency is another characteristic of the transition metals. All other things being equal, for example, iron in the Fe11 form will give a pale blue colour, whereas Fem gives... 

Electronegativity (x) is an empirical measure of the tendency of an atom in a molecule to attract electrons. The noble gases, therefore, do not have electronegativity values because they do not easily form molecules. The electronegativity value depends primarily on the element, but also on the oxidation state, i.e., the electronegativity of elements with variable valency can be different for each valency thus that of Fe2+ is different from that of... 

This has the very important consequence, as we show in more detail later, that no totally symmetric mode of a mixed-valence compound can contribute to the intervalence bandwidth (in the approximation of equal force constants in both oxidation states). For the moment we therefore drop the terms in Q+ and define the dimensionless variables... 

Other metah—a classification given to seven metals that do not fit the characteristics of transition metals. They do not exhibit variable oxidation states, and their valence electrons are found only on the outer shell. They are aluminum, gallium, indium, tin, thallium, lead, and bismuth. 

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 . 

Conversely, the presence of some metal ions of lower oxidation state in the metal ion sublattice requires vacant anion sites to balance the charge. In some cases, the charge imbalance is caused by ions of some other element or, rarely, by multiple valence of the anions. In any event, the empirical formula of a recognizable solid transition metal compound may be variable over a certain range, with nonintegral atomic proportions. Such non-stoichiometric compounds may be regarded as providing extreme examples of impurity defects. 

In Section 24 it was shown that, under favorable conditions, two oxides of the same metal, in different states of valency, may form solid solutions which have been described as compounds with variable composition. The stabilizing factor in this case is the increase in entropy, due to the random distribution of the two positive ions these systems, strictly speaking, are stable only at elevated temperature. The conditions may be such that two oxides form a real compound, because this process is connected with a decrease in energy. The compounds formed in this way have a stoichiometric composition, with two kinds of positive ions in fixed positions, so arranged that the energy of the system is minimal. A good example of a compound of this type is Fe304. 

AHt can be calculated, in principle, from thermochemical data. It is then necessary to take into account the variable valency of most metals and to fix the different oxidation states which occur during stationary or non-stationary reaction conditions. Some difficulties with this method are th scarcity of data for mixed oxides, the difference in conditions between those on the surface of the catalyst and those in the bulk and the inaccuracy of a number of data obtained by measuring differences in AH. 

The (/-block elements tend to lose their valence s-electrons when they form compounds. Most of them can also lose a variable number of d-electrons and show variable valence. The only elements of the block that do not use their (/-electrons in compound formation are the members of Group 12 (zinc, cadmium, and mercury). The ability to exist in different oxidation states is responsible for many of the special properties of these elements and plays a role in the action of many vital biomolecules (Box 16.1). 

The effects of deliberately added donors, such as titanium, and acceptors, such as iron and magnesium, on electrical conductivity have been studied. Doping with aliovalent ions affects the concentration of intrinsic defects and, in consequence, the diffusivity of A1 and O. In the case of variable-valency dopants, changes in p0l change the fraction of dopants in the aliovalent state and the nature and concentration of the defects. For example, the dopant Ti substitutes for A1 and, in the fully oxidized state, produces the defect TiA1, compensated by Va", so that... 

The covalency falls with group member and variable valency is observed in a number of these non-metals. The maximum possible oxidation state increases from +5 in group 15 to +8 in group 18. 

Unlike the 4/orbitals in the lanthanides, the 5/orbitals in the earlier actinide elements are more expanded and so can be engaged in chemical bonding. This leads to a pattern of chemistry more analogous to that found in the d block, with the possibility of variable oxidation states up to the maximum possible determined by the number of valence electrons. Most thorium compounds contain Th(IV) (e.g. Th02) and... 

With very few exceptions they exhibit variable valence, and their ions and compounds are colored in one if not all oxidation states. 

Chlorine is 2s 2p s p — In contrast to fluorine, chlorine forms a series of oxides and oxyacids and exhibits a variable valency. The ion CIO2 has been shown to have a triangular structure which would suggest that the chlorine was in the singly charged positive, divalent state ... 

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