Gaining of electrons

Franklin defined charge as positive or negative in the way we understand the loss or gain of electrons by mechanically rubbing surfaces together. His definition still stands. 

In addition to the case of a metal in contact with its ions in solution there are other cases in which a Galvani potential difference between two phases may be found. One case is the innnersion of an inert electrode, such as platinum metal, into an electrolyte solution containing a substance S that can exist m either an oxidized or reduced fomi tlirough the loss or gain of electrons from the electrode. In the sunplest case, we have... 

Numerous ionic compounds with halogens are known but a noble gas configuration can also be achieved by the formation of a covalent bond, for example in halogen molecules, X2, and hydrogen halides, HX. When the fluorine atom acquires one additional electron the second quantum level is completed, and further gain of electrons is not energetically possible under normal circumstances, i.e... 

The chemical process that produces an electrical current from chemical energy is called an oxidation-reduction reaction. The oxidation-reduction reaction in a battery involves the loss of electrons by one compound (oxidation) and the gain of electrons (reduction) by another compound. Electrons are released from one part of the batteiy and the external circuit allows the electrons to flow from that part to another part of the batteiy. In any battery, current flows from the anode to the cathode. The anode is the electrode where positive current enters the device, which means it releases electrons to the external circuit. The cathode, or positive terminal of the battery, is where positive current leaves the device, which means this is where external electrons are taken from the external circuit. 

It follows that corrosion is an electrochemical reaction in which the metal itself is a reactant and is oxidised (loss of electrons) to a higher valency state, whilst another reactant, an electron acceptor, in solution is reduced (gain of electrons) to a lower valency state. This may be regarded as a concise expression of the electrochemical mechanism of corrosion . 

Fig. 1.20 Cell consisting of two reversible Ag /Ag electrodes (Ag in AgN03 solution). The rate and direction of charge transfer is indicated by the length and arrow-head as follows gain of electrons by Ag -he- Ag—> loss of electrons by Ag - Ag + e- —. (o) Both electrodes at equilibrium and (f>) electrodes polarised by an external source of e.m.f. the position of the electrodes in the vertical direction indicates the potential change. (K, high-impedance voltmeter A, ammeter R, variable resistance)...

The ions dealt with to this point (e.g., Na+, Cl-) are monatomic that is, they are derived from a single atom by the loss or gain of electrons. Many of the most important ions in chemistry are polyatomic, containing more than one atom. Examples include the hydroxide ion (OH-) and the ammonium ion (NH ). In these and other polyatomic ions, the atoms are held together by covalent bonds, for example,... 

These definitions are of course compatible with the interpretation of oxidation and reduction in terms of loss and gain of electrons. An element that loses electrons must increase in oxidation number. The gain of electrons always results in a decrease in oxidation number. 

New chemical specks are produced in each half of the cell. The copper rod is converted to copper ions (the rod loses weight) and the silver ions are changed to metal (the silver rod gains weight). The new species can be explained in terms of gain of electrons (by silver) and loss of electrons (by copper). 

It is often convenient and usually informative to treat oxidation-reduction in terms of halfreactions. When it is convenient, oxidation is involved in the half-reaction showing loss of electrons, and reduction is involved in the halfreaction showing gain of electrons. 

At the cathode, a variety of reduction reactions take place, including the reduction of hydrogen ions (the gaining of electrons) to produce hydrogen gas. 

The removal of oxygen, addition of hydrogen, or gain of electrons. Refractory ... 

We recognize redox reactions by noting whether electrons have migrated from one species to another. The loss or gain of electrons is easy to identify for monatomic ions, because we can monitor the charges of the species. Thus, when Br ions are converted into bromine atoms (which go on to form Br2 molecules), we know that each Br ion must have lost an electron and hence that it has been oxidized. When 02 forms oxide ions, 02-, we know that each oxygen atom must have gained two electrons and therefore that it has been reduced. The difficulty arises when the transfer of electrons is accompanied by the transfer of atoms. For example, is chlorine gas, Cl2, oxidized or reduced when it is converted into hypochlorite ions, CIO" ... 

The key to writing and balancing equations for redox reactions is to think of the reduction and oxidation processes individually. We saw in Section K that oxidation is the loss of electrons and reduction the gain of electrons. 

When balancing redox equations, we consider the gain of electrons (reduction) separately from the loss of electrons (oxidation), express each of these processes as a halfreaction, and then balance both atoms and charge in each of the two half-reactions. When we combine the halfreactions, the number of electrons released in the oxidation must equal the number used in the reduction. 

Direct Electron Transfer. We have already met some reactions in which the reduction is a direct gain of electrons or the oxidation a direct loss of them. An example is the Birch reduction (15-14), where sodium directly transfers an electron to an aromatic ring. An example from this chapter is found in the bimolecular reduction of ketones (19-55), where again it is a metal that supplies the electrons. This kind of mechanism is found largely in three types of reaction, (a) the oxidation or reduction of a free radical (oxidation to a positive or reduction to a negative ion), (b) the oxidation of a negative ion or the reduction of a positive ion to a comparatively stable free radical, and (c) electrolytic oxidations or reductions (an example is the Kolbe reaction, 14-36). An important example of (b) is oxidation of amines and phenolate ions ... 

Reduction Is the gain of electrons by a substance. Oxidation and reduction always occur together. 

Any reaction of the type described herein can, in principle, form the basis of electricity generation. The only requirement is that site of oxidation (loss of electrons or deelectronation) be physically separated from the site of reduction (gain of electrons or electronation) so that the reaction cannot be completed without the passage of an electric current from one site to the other, except through the external circuit. If there is no external connection between the electrodes, equilibria will exist and each of the metals concerned will have a potential relative to the corresponding electrolyte. These potentials will be different for the two metals. 

Oxidation-reduction (redox) reactions involve the loss of electrons and increase in oxidation number (oxidation) by one substance or system, with an associated gain of electrons and decrease in oxidation number (reduction) by another substance or system. Thus for every oxidation reaction there must be a reduction reaction. The oxidation number of an atom represents the hypothetical charge an atom would have if the ion or molecule were to dissociate.46-47... 

Reduction of a chemical species involves the gain of electrons by that species. Because the solutions of alkali metals in liquid ammonia contain free electrons, they are extremely strong reducing agents. This fact has been exploited in a large number of reactions. For example, oxygen can be converted to superoxide or peroxide ions. 

Ionization The process by which neutral atoms become either positively or negatively electrically charged by the loss or gain of electrons. 

Oxidation loss of electrons reduction gain of electrons (OIL RIG). 

Oxidation is loss of electrons. Reduction is gain of electrons. 

Care we write a formal charge with Arabic numerals, and means that the full charge exists as indicated Cu2+ means a copper atom with fully two electronic charges missing. We write an oxidation number with Roman numerals, and does not relate to any physical loss or gain of electrons it is purely a book-keeping exercise. Mnvn does not mean that a manganese atom has lost seven electrons. 

Redox is a term that stands for reduction and oxidation. Reduction is the gain of electrons and oxidation is the loss of electrons. In these reactions, the number of electrons gained must be identical to the number of electrons lost. For example, suppose a piece of zinc metal is placed in a solution containing the Cu2+ cation. Very quickly, a reddish solid forms on the surface of the zinc metal. That substance is copper metal. At the molecular level, the zinc metal is losing electrons to form the Zn2+ cation and the Cu2+ ion is gaining electrons to form copper metal. We can represent these two processes as ... 

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