Electrons in oxidation-reduction reactions

Oxidation states A concept that provides a way to keep track of electrons in oxidation-reduction reactions according to certain rules. 

The transfer of phosphoryl groups is a central feature of metabolism. Equally important is another kind of transfer, electron transfer in oxidation-reduction reactions. These reactions involve the loss of electrons by one chemical species, which is thereby oxidized, and the gain of electrons by another, which is reduced. The flow of electrons in oxidation-reduction reactions is responsible, directly or indirectly, for all work done by living organisms. In nonphotosynthetic organisms, the sources of electrons are reduced compounds (foods) in photosynthetic organisms, the initial electron donor is a chemical species excited by the absorption of light. The path of electron flow in metabolism is complex. Electrons move from various metabolic intermediates to specialized electron carriers in enzyme-catalyzed reactions. 

The concept of oxidation states (also called oxidation numbers) provides a way to keep track of electrons in oxidation-reduction reactions. Oxidation states are defined by a set of rules, most of which describe how to divide up the shared electrons in compounds containing covalent bonds. However, before we discuss these rules, we need to discuss the distribution of electrons in a bond. 

Chapter 13. For now we will be satisfied with some general guidelines to help us keep track of electrons in oxidation-reduction reactions. The nonmetals with the highest attraction for shared electrons are in the upper right-hand corner of the periodic table. They are fluorine, oxygen, nitrogen, and chlorine. The relative ability of these atoms to attract shared electrons is... 

Chemists use some important terminology to describe the movement of electrons in oxidation-reduction reactions. Oxidation is the loss of electrons, and reduction is the gain of electrons. (The original meaning of reduction comes from the process of reducing large amounts of metal ore to smaller amounts of metal, but you ll see shortly why we use the term reduction for the act of gaining.)... 

Metal ions, which have a positive charge, contribute to the catalytic process by acting as electrophiles (electron-attracting groups). They assist in binding of the substrate, or they stabilize developing anions in the reaction. They can also accept and donate electrons in oxidation-reduction reactions. 

The concept of oxidation states (sometimes called oxidation numbers) lets us keep track of electrons in oxidation-reduction reactions by assigning charges to the various atoms in a compound. Sometimes these charges are quite apparent. For example, in a binary ionic compound the ions have easily identified charges in sodium chloride, sodium is +1 and chlorine is -1 in magnesium oxide, magnesium is +2 and oxygen is -2 and so on. 

What unifies the various definitions of an equivalent is that, in each case, one equivalent supplies or accepts 1 mole of unit charges—in the form of protons (in acid-base reactions), or electrons (in oxidation-reduction reactions), or the ions themselves (in ion combinations). Because electric charge is strictly conserved, the number of moles of charge supplied by one reactant must equal the number of moles of charge accepted by the other reactant. Thus, the system of equivalence is merely a convenient but arbitrary scheme for rebalancing equations such that 1 eq of one substance reacts exactly with 1 eq of another substance to produce 1 eq of each product. For example, the reaction written as... 

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