Positive oxidation states

Exists as the (Hg —Hg) ion. Other polymercury cations, e.g. Hgj (Hg plus AsFj), Hg4 etc., are also known. All positive oxidation state compounds of Hg are readily reduced to the metal, mercury chlorides... 

Meta/ Oxides. The metal oxides aie defined as oxides of the metals occurring in Groups 3—12 (IIIB to IIB) of the Periodic Table. These oxides, characterized by high electron mobiUty and the positive oxidation state of the metal, ate generally less active as catalysts than are the supported nobel metals, but the oxides are somewhat more resistant to poisoning. The most active single-metal oxide catalysts for complete oxidation of a variety of oxidation reactions are usually found to be the oxides of the first-tow transition metals, V, Cr, Mn, Fe, Co, Ni, and Cu. 

The halogens, except fluorine, can be oxidized to positive oxidation states. Most commonly you will encounter these positive oxidation states in a set of compounds called halogen oxyacids and their ions. 

Metals exist in nature primarily in positive oxidation states, and many form stable com-poimds in more than one oxidation state. The formal oxidation number of the most common form can range from -t-1 to +6. The stable form in a given environment depends on the oxidation potential and chemical composition of that environment. Often the stable form at the Earth s surface in the presence of molecular... 

Pd catalysts were active and enantioselective only when reduced at low temperature, suggesting that dissociative adsorption of the reactant was dependent on the presence of surface Pd atoms in a positive oxidation state... 

In aqueous geochemistry, the important distinguishing property of metals is that, in general, they have a positive oxidation state (donate electrons to form cations in solution), but nonmetals have a negative oxidation state (receive electrons to form anions in solution). In reality, there is no clear dividing line between metals and nonmetals. For example, arsenic, which is classified as a nonmetal, behaves like a metal in its commonest valence states and is commonly listed as such. Other nonmetals, such as selenium, behave more like nonmetals. 

The oxygen must exist in a -2 oxidation state, because it is more electronegative than is sulfur. Therefore, sulfur must exist in two different positive oxidation states in the two compounds. Its maximum oxidation state is + 6, corresponding to its position in periodic group VIA. It also has an oxidation state of +4. 2 less than its maximum (see Fig. 13-1). The formulas therefore arc SO, and SO,. 

The oxidation state of an element in a compound is an indication of how many electrons each atom of that element has lost (positive oxidation state) or gained (negative). Since oxidation state is determined by a set of rules, rather than by experiment, its connection to the number of electrons actually transferred is rather tenuous. It is used in naming compounds and balancing some chemical equations. 

Bromine combines with nonmetals according to the lowest positive oxidation state of the nonmetal. For example,... 

The well-known rule that positive oxidation states are stabilized by coordination may be called the first stabilizing rule. This rule relates oxidizing properties and complex stability the higher the complex stability, the more negative the redox potential. We can also say that... 

Tracer studies of the chemical properties showed that astatine was soluble in organic solvents, could be reduced to the —1 state, and had at least two positive oxidation states. These studies were made on solutions of 10-11 to KL15 molar astatine (29). The similarity between astatine and iodine was found to be less close than that between technetium and rhenium or that between promethium and the other rare earths (30). 

Naskar et al. (1997) were interested in using bond valences to determine oxidation states around transition-metal cations, particularly those with negative or zero formal oxidation states. Since these numbers cannot, in principle, be reached by the standard equations, they proposed to create a fictional positive oxidation state by arbitrarily adding 4.0 to the actual oxidation state. They proposed to write the valence sum rule in the form of eqn (A 1.10) ... 

The cyanide ion, CN, is isoelectronic with carbon monoxide and has an extensive chemistry of reaction with transition metals (e.g. the formation of the hexacyanoferrate(III) ion, [Fe(CN)63 ] by reaction with iron(III) in solution) but, unlike CO, it shows a preference for the positive oxidation states of the elements. This is mainly because of its negative charge. 

The two positive oxidation states of P (+ 5 and + 3) are both more stable than their nitrogen equivalents, and phosphoric acid has no oxidant properties apart from those given by the hydrated protons produced from it in aqueous solution. A dilute solution of phosphoric acid will provide a sufficiently high concentration of hydrated protons to oxidize any metal to its most stable state, providing the reduction potentials for the metal ion/metal couple are negative. 

In alkaline solution there is a general stabilization of the positive oxidation states of the elements of the group and a destabilization of the negative oxidation states. 

All the positive oxidation states of the Group 17 elements are powerful oxidants. In alkaline conditions the positive oxidation states are still reasonably powerful oxidants, e.g. HOC1 is the basis of some household bleach solutions which allegedly kill all known germs. Dilute chloric(VII) acid has a high reduction potential, but reacts very slowly with most reducing agents. 

A computer literature search revealed no direct analytical method specific for sodium dichloroisocyanurate dihydrate (NaDCC) or trichloroisocyanuric acid (TCCA). Each compound dissolved in water released chlorine in the positive oxidation state and formed complex equilibria reactions dependent on the pH of the solutions. NaDCC and TCCA are very strong oxidants and very reactive compounds, therefore, incompatible for chromatographic analysis. The only method that is used for analysis of compounds containing... 

In a series of late transition metal catalyzed processes the first step in the catalytic cycle is the coordination of the reagent to the metal atom, which is in a positive oxidation state, followed by its covalent attachment through the concomitant breaking of an unsaturated carbon-carbon bond or a carbon-hydrogen bond. These processes usually require a highly electrophilic metal centre and are frequently carried out in an intramolecular fashion. The carbometalation processes that follow a similar course, but take place only at a later stage in the catalytic cycle, will be discussed later. 

Although many of the compounds of the halogens discussed thus far have exhibited a halogen in a positive oxidation state, most of the chemistry of this family involves either halide ions or covalent molecules in which the halogen is the most electronegative atom. 

Porterfield. W. W., 295 Positive oxidation states, halogens in, 837-848 Posttransition metals, 28. 876 Potassium, 309, 582-587 Potentials, electrode, 378-383 Pourbaix diagram, 591-592 Praseo complex, 388,491, 493 Predominance area diagram, 591 Prewitt, C. T., 116-117 Principal axis, 51 Prism, trigonal prism, 489-491 Probability function, 13 Prosthetic group, 919 Proteins, and blue copper proteins, 912-916 Proton... 

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