Oxidation number defined

The concept of oxidation number leads directly to a working definition of the terms oxidation and reduction. Oxidation is defined as an increase in oxidation number and reduction as a decrease in oxidation number. Consider once again the reaction of zinc with a strong acid ... 

Classical complexes are identified [1112] as those species in which the central metal ion possesses a well-defined oxidation number and a set of ligands with a discrete electron population. Non-classical complexes , in contrast, involve highly covalent and/or multiple metal-ligand bonding resulting in indistinct oxidation numbers for both participants. 

Chemists have found a way to keep track of electrons by assigning an oxidation number to each element. The oxidation number is defined so that... 

Formal charge and oxidation number are two ways of defining atomic charge that are based on the two limiting models of the chemical bond, the covalent model and the ionic model, respectively. We expect the true charges on atoms forming polar bonds to be between these two extremes. 

We learned to write formulas of ionic compounds in Chaps. 5 and 6. We balanced the charges to determine the number of each ion to use in the formula. We could not do the same thing for atoms of elements in covalent compounds, because in these compounds the atoms do not have charges. In order to overcome this difficulty, we define oxidation numbers, also called oxidation states. 

Whether zinc is a main-group or transition metal depends, of course, on one s definition of transition metal and main-group metal. Those who classify zinc as a main-group metal cite its (almost) exclusive oxidation number of +2 in compounds (but see Section 2.06.15.2) and the absence of a partially filled r/ shell in the metal and its compounds. Those who classify zinc as a transition metal usually note its much greater effective nuclear charge, polarizing power and its limited, but well defined, coordination chemistry. 

The terms oxidation and reduction, as should be obvious from the discussion to this point, can be defined in two different ways—according to the gain or loss of electrons, or according to the increase or decrease in oxidation number ... 

Define oxidation, reduction, oxidation number, oxidizing agent, and reducing agent. 

Four rules apply when assigning oxidation numbers to atoms. First, the oxidation number of each atom in a pure element is defined as zero. Therefore, elemental carbon (graphite or diamond) has an oxidation number of 0, as does an atom in metallic iron, or each of the 2 hydrogen atoms in the Fl2 molecule ... 

Models with three or more stereogenic centers create new problems. Again, carbohydrate chemists were first to give efficient and clear, though perhaps to the outsider cumbersome solutions. The following carbohydrate convention (see Table 11) is based on the Fischer projection. i.e., it prescribes an all-eclipsed conformation of the backbone and defines the direction of the backbone by the oxidation numbers of the terminal carbon atoms. 

Oxidutlon number. Tlie oxidation number of a central atom in a coordination entity is defined as the charge K would bear if all the ligands were removed along with the electron pairs that were shared with the central atom. It is represented by a roman numeral. 

Charge numbers, oxidation numbers, and ionic proportions. When the oxidation number of the central atom can be defined without ambiguity, it may be indicated by appending a roman numeral to the central atom name.2 This number is enclosed in parentheses after the part of the name denoting the central atom. No positive sign is used. When necessary a negative sign is placed before the number. Arabic zero indicates the zero oxidation number. No space is left between this number and the rest of the name. 

Figure 13.4.4 Classification of H atoms in 4,4-difluorobutanoic acid as defined in the model of Ghose et al. [49,50], The subscript represents hybridization and the superscript is the formal oxidation number. X represents any heteroatom (O, N, S, P, Se, and halogens).

The results from the TBA test, known in older literature as the TBA number, are usually expressed as mg malonaldehyde/kg sample for methods a to c cited above (note that results have also been reported as nmol malonaldehyge/kg or g sample) and as mg of malonaldehyde per unit of lipid for method d. Since it is known that malonaldehyde is not the only aldehyde present in the sample extract and because other aldehydes are capable of producing the same red pigment with TBA when the conditions are favorable, the TBA number/value is more appropriately expressed as the TBARS value, i.e., mg malonaldehyde equivalents/kg sample. To confuse the matter, the AOCS method, which is based on the protocol reported by Pokomy and Dieffenbacher (1989) and permits the direct determination of TBA value in oils and fats without preliminary isolation of secondary oxidation products, defines the TBA value as the increase of absorbance measured at 532 nm due to the reaction of the equivalent of 1 mg of sample per 1 ml volume with... 

We were quite optimistic in the beginning as the second reduction process corresponds to the formation of a black deposit which was potentially the first electrochemical route to make thick tantalum layers. After having washed off all ionic liquid from the sample we were already a bit sceptical as the deposit was quite brittle and did not look metallic. The SEM pictures and the EDX analysis supported our scepticism and the elemental analysis showed an elemental Ta/Cl ratio of about 1/2. Thus, overall we have deposited a low oxidation state tantalum choride. Despite the initial disappointment we were still eager to obtain the metal and found some old literature from Cotton [122], in which he described subvalent clusters of molybdenum, tungsten and tantalum halides. In the case of tantalum the well-defined Ta6Cli22+ complex was described with an average oxidation number of 2.33 and thus with a Ta/Cl molar ratio very close to 1/2. Such clusters are depicted in Figure 4.15. 

In order to keep track of electron shifts in oxidation-reduction reactions, it is convenient to use the concept of oxidation number or oxidation state of various atoms involved in oxidation-reduction reactions. The oxidation number is defined as the formal charge which an atom appears to have when electrons are counted in accordance with the following rather arbitrary rules. 

With such a definition in mind, one envisions that an electron will be transferred as a unit and thus reaches the conclusion that the resultant charge must be an integer. Alternately, Shriver, Atkins and Langford [12] seem to have no problem with fractional oxidation numbers and define the term as ... 

The combination of TOC and COD measurements was used to introduce the MOC-concept of the mean oxidation number of carbon (Vogel et al., 2000). This concept may be useful to distinguish between oxidative, reductive and physical processes that are related to the diminution of the organic carbon content during water treatment. The MOC value is defined according to Equation 5-1. 

The oxidation number, also known as the oxidation state, of an atom in a compound (or in a free element or polyatomic ion) is defined as the number of electrons possessed by a free (an uncombined) atom of the element— Nf ee—minus the number that is assigned to the atom in the compound (or element or ion)—... 

Oxidation numbers (also called oxidation states) are used as a sort of bookkeeping method for keeping track of the electrons in polyatomic ions or compounds that have covalent bonds. (For monatomic ions, the charge on the ions works just as well.) Oxidation number is defined as the number of electrons in a free atom minus the number controlled by that atom in the compound. The control of electrons in a covalent bond is assigned to the more electronegative atom of the bond. Eight simple rules can be used to determine the oxidation number of an element from the formula of its compound or ion (Section 16.1). 

Oxidation is defined as a gain in oxidation number, caused by a loss of electrons or of control of electrons. Reduction is defined as a loss in oxidation number, caused by a gain of electrons or of control of electrons. Complicated oxidation-reduction equations must be balanced according to some systematic method because they are too complex to be balanced by inspection. Although neither can take place alone, the oxidation and the reduction can occur in different locations if suitable electrical connections are provided. (Chapter 17) In the halfreaction method, the equation for the half-reaction involving oxidation and that for the half-reaction involving reduction are balanced separately then the two are combined. Each may be multiplied by a small integer if necessary to balance the numbers of electrons involved. 

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