Definition of oxidation state

The definition of oxidation state used herein is the charge left on the central metal after the ligands have been removed in their normal closed shell configurations. Inasmuch as this definition is based on valence-bond formalism, there are several instances of indefinite oxidation state (see Section III). It is recognized that oxidation state is not a measurable physical quantity. However, the concepts of oxidation state and d-electron configuration which are used throughout this chapter are generally useful... 

Other ions which are reduced in the reductor to a definite lower oxidation state are those of titanium to Ti3+, chromium to Cr2+, molybdenum to Mo3+, niobium to Nb3+, and vanadium to V2 +. Uranium is reduced to a mixture of U3 + and U4+, but by bubbling a stream of air through the solution in the filter flask for a few minutes, the dirty dark-green colour changes to the bright apple-green colour characteristic of pure uranium(I V) salts. Tungsten is reduced, but not to any definite lower oxidation state. 

By careful control of the conditions of the reaction one can obtain preferentially oxidation of sulfur to its four coordinate oxidation state and by using a second set of conditions one can obtain the oxidation to the six-coordinate sulfur species. The dynamic NMR study of SF3CF2SF3 is currently in progress in collaboration with A. H. Cowley (60). This differentiation of oxidation states is extremely promising, and work in progress shows that this is not at all an isolated situation. Mercaptans and other organosulfur compounds definitely exhibit this capacity in fluorine reactions. 

Redox reactions are better defined in terms of the concept of electron transfer. Thus an atom is said to be oxidized if, as the result of a reaction, it experiences a net loss of electrons and is reduced if it experiences a net gain of electrons. This simple definition can be used to identify oxidation or reduction processes at carbon in terms of a scale of oxidation states for carbon based on the electronegativities of the atoms attached to carbon. The idea is to find out whether in a given reaction carbon becomes more, or less, electron-rich. We will use the following somewhat arbitrary rules ... 

The definitions of oxidation and reduction may now be generalized as follows The increase in oxidation state is oxidation and the decrease in oxidation state is reduction. In the reduction of Mn02 to Mn, for example, the oxidation state of manganese is changed from -f4 to -t-2 in the oxidation of H3ASO3 to HAs04, the oxidation state of arsenic is changed from -1-3 to -1-5. 

Apart from availability (Section 1.2.1), there is another more chemical approach to commonality that we should dwell on, an aspect that we have touched upon already. This is a definition in terms of oxidation states. With the most common of all metals in the Earth s crust, the main group element aluminium, only one oxidation state is important - Al(III). However, for the most common transition metal (iron), both Fe(II) and Fe(III) are common, whereas other higher oxidation states such as Fe(IV) are known but very uncommon. With the rare element rhenium, the reverse trend holds true, as the high oxidation state Re(VI) is common but Re(III) and Re(II) are rare. What is apparent from these observations is that each metal can display one or more usual oxidation states and a range of others met much more rarely, whereas some are simply not accessible. 

This chapter is concerned with equilibria involving oxidation and reduction processes. Firstly, we review concepts that will be familiar to most readers definitions of oxidation and reduction, and the use of oxidation states (oxidation numbers). 

One result of this work is the conclusion that in chromia-alumina, and in other supported oxides, there must be local concentration of the supported oxide. This conclusion is reached because the Weiss constant shows definite indication of exchange interaction at concentrations of the paramagnetic ion too low to cover the surface of the support with even a monolayer. Another conclusion is that the support is sometimes able to modify the relative stabilities of oxidation states in the supported oxide. For instance, manganese oxide supported on gamma-alumina tends to be stabilized in the tripositive state, while on high-area titania it reverts to the tetrapositive state. 

A number of transition metals can be determined conveniently if their cations undergo a definite change of oxidation state see Oxidation Number) on titration with a standard solution of potassium permanganate, potassium dichromate, cerium(IV) sulfate, or ammonium hexanitratocerate(IV). Several visual indicators have been proposed, including diphenylamine and its derivatives, xylene cyanole FF, and especially A-phenylanthranilic acid and tris(l,10-phenanthroline)iron(II) sulfate ( ferroin ). Solutions of have been used in the determination of iron, copper, titanium, vanadium, molybdenum, tungsten, mercury, gold, silver, and bismuth, and standard solutions of and Sn F U, and and Mo have also... 

Write two definitions of oxidation. In the first definition, use the phrase oxidation state. In the second definition, use the term electrons. 

Another concept that is fundamental to an understanding of homogeneous catalysis is that of the oxidation state of a complex. Although commonly used in general chemistry, a less puristic definition of this state, which may be regarded as a formalism more suited to transition-metal complexes, has become the cornerstone of homogeneous catalysis. 

Plan First, we assign oxidation states, or numbers, to all the atoms and determine which elements change oxidation state. Second, we apply the definitions of oxidation and reduction. 

No definitive evidence has been founc in preliminary studies/ for the existence of oxidation states intermediate between... 

This definition of oxidation and reduction applies only to reactions in which electron transfer occurs - i.e. to reactions involving ions, it can be extended to reactions between covalent compounds by using the concept of oxidation number (or state). This is a measure of the electron control that an atom has in a compound compared to the atom in the pure element. An oxidation number consists of two parts ... 

Today inorganic chemists do not use such terms as "primary" (Haupt) and "secondary" Neberi) valence but instead speak of "oxidation state" and "coordination number." One modem popular definition for the term "oxidation state" is "The oxidation state of a metal in a complex is... 

There is one way in which the actinide series definitely differs from the lanthanide series. This is in the existence of oxidation states higher than IV [protactinium (V), uranium(VI), neptunium (VI), plutonium (VI)] in this series. It must be concluded that the 5f electrons are not so tightly bound as the 4f electrons. This is certainly reasonable. However, the evidence so far is in favor of a maximum oxidation number of VI in this series, so that the removal of three electrons, or four if there are no electrons in the 6d orbitals, from the 5f orbitals is the maximum that occurs in ordinary chemical reactions. 

The definitions of oxidation and rednction and potential sources of confusion associated with them are discussed in Sect. VII.1. Some chemists mistakenly think that hydration of ethylene to give ethanol is an oxidation process, but no net oxidation or reduction takes place in hydration of ethylene. On the other hand, hydration of ethylene-palladium complexes to give acetaldehyde (the Wacker oxidation) (Sect. V.3.1) is a genuine two-electron oxidation reaction. If one determines the formal oxidation states (FOS) of the participating atoms (i.e., C and Pd) in the examples shown in Scheme 1, the difference between simple alkene hydration and the Wacker oxidation (Sect. V.3.1.1) is very clear. The formal oxidation states of the other atoms in these reactions do not change. 

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