Oxidation States Electron Bookkeeping

For many redox reactions, such as those involving oxygen or other highly electronegative elements, the substances being oxidized and reduced can be identified easily by inspection. For other redox reactions, identification is more difficult. For example, consider the redox reaction between carbon and sulfur. 

Do not confuse oxidation state with ionic charge. A substance need not be ionic to have an assigned oxidation state. 

What is oxidized here What is reduced In order to easily identify oxidation and reduction, chemists have devised a scheme to track electrons and where fiiey go in chemical reactions. In this scheme— which is like bookkeeping for electrons—all shared electrons are assigned to the most electronegative element. Then a number—called the oxidation state or the oxidation number— is computed for each element based on the number of electrons assigned to it. 

The procedure just described is a bit cumbersome in practice. However, its main results can be summarized in a series of rules. The easiest way to assign oxidation states is to follow these rules. 

These rules are hierarchical. If any two rules conflict, follow the rule that Is higher on the list. 

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Oxidation States Electron Bookkeeping 581 16.8 Corrosion Undesirable Redox Reactions 598... 

The oxidation number, or oxidation state, is a bookkeeping device used to keep track of the number of electrons formally associated with a particular element. The oxidation number is meant to tell how many electrons have been lost or gained by a neutral atom when it forms a compound. Because oxidation numbers have no real physical meaning, they are somewhat arbitrary, and not all chemists will assign the same oxidation number to a given element in an unusual compound. However, there are some ground rules that provide a useful start. 

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). 

The assignment of oxidation states is a bookkeeping method by which charges are assigned to the various atoms in a compound. This method allows us to keep track of electrons transferred between species in oxidation-reduction reactions. 

Indeed, the application of transition-metal catalysis in organic synthesis is built around many such formalisms. In addition to the formal oxidation state, these include coordinative unsaturation, coordination number, and coordination geometry, hydride formalism and the 18-electron and 16-18-electron rules, also referred to as electron bookkeeping. 

This rule arises from the assumption that the valence shell electrons of the metals are all in the Nd shell, where N is the principal quantum number. From quantum theory considerations, the d levels are usually associated with the highest energies and are hence the most amenable to the exchange of electrons. Because the number of electrons is related to the oxidation state of a metal, it is clear that the number of d electrons, denoted by d", determines this state. This bookkeeping function of the d orbitals in determining the oxidation state of the complex is best illustrated by its usefulness in formulating a rule for the maximum allowable number of ligands for each d . The rule in its final form, known as the 18-electron rule, is... 

This joke hinges on the fact that when an atom loses an electron, it becomes a positively charged ion (also known as a cation). Jokes aside, this chapter is all about electronic bookkeeping. In chemistry, electrons underlie almost all reactions, whether they are being excited, forming bonds, and so on. Oxidation states are simply a way to keep track of where all those electrons are going. 

Carbon went from an oxidation state of 0 to +4. In terms of our electron bookkeeping scheme (the assigned oxidation state), carbon lost electrons and was oxidized. Sulfur went from an oxidation state of 0 to —2. In terms of our electron bookkeeping scheme, sulfur gained electrons and was reduced. 

Two different electron bookkeeping methods formal charge vs. oxidation state. 

Chemists have devised a bookkeeping system to monitor which atom loses electron charge and which atom gains it each atom in a molecule (or formula unit) is assigned an oxidation number (O.N.), or oxidation state, which is the charge the atom would have if electrons were transferred completely, not shared. 

In KO2, oxygen has a -j oxidation state. Although this seems unusual, it is accepted because oxidation states are merely an imposed electron bookkeeping scheme, not an actual physical quantity. 

An oxidation state is a fictitious charge given to each atom in a redox reaction by assigning all shared electrons to the atom with the greater attraction for those electrons. Oxidation states are an imposed electronic bookkeeping scheme, not an actual physical state. 

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