Loss of Electrons

We have seen that atoms like to get a noble gas configuration when they react so that the compound formed will be stable (Units 2.1 and 2.2). Some atoms can achieve this by giving away or losing electrons. What holds the electrons in the atom in the first place  

In Group 1 of the periodic table, the first element is lithium. Its electronic configuration is 2 1 (two electrons in the first shell and one in the second). To get a noble gas structure, it has to lose the electron from the outermost shell. The next element is sodium, with configuration 2 8 1. Sodium also has to lose one electron, but this electron is in the third shell from the nucleus, and thus easier to lose. The next element, potassium, with configuration 2 8 8 1, again has to lose one electron, but this electron is in the fourth shell, still further away from the nucleus and thus even easier to lose. 

In other words, as you go down a group in the periodic table, it gets easier and easier for atoms to lose an electron and form a positive ion. This is true for any group, not just for Group 1. 

Name Atomic number First ionisation energy Ik mol Atomic radiusipm 

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Oxidation—the loss of electrons by a constituent in a chemical reaction. 

Biooxidation Oxidation (loss of electrons) process accelerated by a biocatalyst. 

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)...

Oxidation loss of electrons by a species during a chemical or electrochemical reaction addition of oxygen or removal of hydrogen from a substance. 

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. 

By the half-cell potentials, we conclude the Zn-Zn+2 half-reaction has the greater tendency to release electrons. It will tend to transfer an electron to silver ion, forcing (54) in the reverse direction. Hence we obtain the net reaction by subtracting (54) from (52). But remember that this subtraction must be in the proportion that causes no net gain or loss of electrons. If two electrons are lost per atom of zinc oxidized in (52), then we must double half-reaction (54) so that two electrons will be consumed. 

The ion Fe2+ is converted into ion Fe3+ (oxidation), and the neutral chlorine molecule into negatively charged chloride ions Cl" (reduction) the conversion of Fez+ into Fe3+ requires the loss of one electron, and the transformation of the neutral chlorine molecule into chloride ions necessitates the gain of two electrons. This leads to the view that, for reactions in solutions, oxidation is a process involving a loss of electrons, as in... 

Now the gain and loss of electrons must be equal. One permanganate ion utilises 5 electrons, and one iron(II) ion liberates 1 electron hence the two partial equations must apply in the ratio of 1 5. 

Ferrell, R. A., and Quinn, J., Phys. Rev. 108, 570, Characteristic energy loss of electrons passing through metal foils Momentum exciton model of plasma oscillations/ ... 

Apart from generating the cupric ion, the acidic oxidation reaction (loss of electrons) produces cuprous ion as an intermediate from any cuprous oxide that may be present in the deposit. It is therefore neces-... 

Addition of oxygen, removal of hydrogen or loss of electrons. Oxygenation Treatment ... 

See also Oxidation, Reduction). Some dissolved substances in water occur either in an oxidized or a reduced form, and their state can be changed by either the acquisition of electrons (reduction) or the loss of electrons (oxidation). This transfer system is an reduction-oxidation system, or redox. (Red. - Oxid. n+ = ne—, where n is number of electrons involved), and can be used to measure and... 

Loss of electrons from the polymer chain with the formation of radical cations (polarons) and dications (bipolarons). 

We can often recognize loss of electrons by noting the increase in the charge of a species. This rule also applies to anions, as in the oxidation of bromide ions (charge —1) to bromine (charge 0) in a reaction such as the one used commercially to make bromine (Fig. K.2) ... 

The protons come from the water molecules that hydrate these metal cations in solution (Fig. 10.19). The water molecules act as Lewis bases and share electrons with the metal cations. This partial loss of electrons weakens the O -H bonds and allows one or more hydrogen ions to be lost from the water molecules. Small, highly charged cations exert the greatest pull on the electrons and so form the most acidic solutions. 

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. 

A strongly negative standard potential indicates a tendency to undergo oxidation, which involves loss of electrons. Elements at the left of the d block have lower ionization energies than those at the right. 

Table 1-2 for example, reveal the loss of electrons from the 45 shell in preference to the >d, so that in these species the 45 orbitals are the higher in energy. 

In biologic systems, as in chemical systems, oxidation (loss of electrons) is always accompanied by reduction of an electron acceptor. 

The loss of electrons by magnesium atoms to form Mg cations indicates that this reaction between magnesium metal and hydronium ions involves oxidation and reduction. An atom of magnesium is oxidized, losing two electrons to form a Mg + cation. Because electrons must be conserved in every chemical process, electrons lost by Mg must be gained by some other species. In this example the electrons lost by Mg are gained by H3 O , which is reduced to form H2 and H2 O. 

Experiments and calculations both indicate that electron transfer from potassium to water is spontaneous and rapid, whereas electron transfer from silver to water does not occur. In redox terms, potassium oxidizes easily, but silver resists oxidation. Because oxidation involves the loss of electrons, these differences in reactivity of silver and potassium can be traced to how easily each metal loses electrons to become an aqueous cation. One obvious factor is their first ionization energies, which show that it takes much more energy to remove an electron from silver than from potassium 731 kJ/mol for Ag and 419 kJ/mol for K. The other alkali metals with low first ionization energies, Na, Rb, Cs, and Fr, all react violently with water. 

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