Reactions of Metals with Nonmetals Oxidation-Reduction

In Chapter 3 we spent considerable time discussing ionic compounds— compounds formed in the reaction of a mefal and a nonmetal. A typical example is sodium chloride, formed by fhe reaction of sodium mefal and chlorine gas  

By what process do the neutral atoms become ions The answer is that one electron is transferred from each sodium atom to each chlorine atom. 

After the electron transfer, each sodium atom has fen electrons and eleven protons (a net charge of 1+), and each chlorine atom has eighteen electrons and seventeen protons (a net charge of 1-). 

Thus the reaction of a metal with a nonmetal to form an ionic compound involves the transfer of one or more electrons from the metal (which forms a cation) to the nonmetal (which forms an anion). This tendency to transfer electrons from metals to nonmetals is the third driving force for reactions that we listed in Section 8.1. A reaction that involves a transfer of electrons is called an oxidation-reduction reaction. 

Why can metal-nonmetal reactions always be assumed to be oxidation-reduction reactions  

Reactions of Metals with Nonmetals (Oxidation-Reduction) 

To learn the general characteristics of a reaction between a metal and a nonmetal. To understand electron transfer as a driving force for a chemical reaction. 

Let s examine what happens in this reaction. Sodium metal is composed of sodium atoms, each of which has a net charge of zero. (The positive charges of the eleven protons in its nucleus are exactly balanced by the negative charges on the eleven electrons.) Similarly, the chlorine molecule consists of two uncharged chlorine atoms (each has seventeen protons and seventeen electrons). However, in the product (sodium chloride), the sodium is present as Na and the chlorine as Cl . By what process do the neutral atoms become ions The answer is that one electron is transferred from each sodium atom to each chlorine atom. 

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For each of the following oxidation-reduction reactions of metals with nonmetals, identify which element is oxidized and which is reduced. 

Oxidation-reduction reactions may affect the mobility of metal ions by changing the oxidation state. The environmental factors of pH and Eh (oxidation-reduction potential) strongly affect all the processes discussed above. For example, the type and number of molecular and ionic species of metals change with a change in pH (see Figures 20.5-20.7). A number of metals and nonmetals (As, Be, Cr, Cu, Fe, Ni, Se, V, Zn) are more mobile under anaerobic conditions than aerobic conditions, all other factors being equal.104 Additionally, the high salinity of deep-well injection zones increases the complexity of the equilibrium chemistry of heavy metals.106... 

I really like to call my interest the study of oxidation-reduction (redox) reactions, and insofar as such reactions between metal ions are concerned, there was little prior work when I began my own. Werner had encountered redox reactions in the coirrse of his research and, in fact, made good use of them in the preparative procedures he developed. I m not sure that he thought much about the fundamental difference between them and the reactions he was primarily interested in, which were substitution reactions of metal complexes (coordination complexes). Many of the basic ideas underlying redox reactions were developed in the study of nonmetal chemistry. For example, my mentor at Berkeley became an expert in the redox chemistry of halogenates, after working with Professor Luther in Germany in the first part of this century. 

In contrast to the BSD anion-forming reductions of BSD with the more electropositive metals, the oxidation of BSD with the most electronegative nonmetals does not lead to the BSD cation. The products of reaction of BSD with halogens (even at very low temperatures) are nitrogen and trimethyl-halosilane (50) [Eq. (56)]. 

Oxidation states are used for two purposes to determine if a redox reaction has occurred, and to balance the redox equations. In Chap. 3, oxidation was defined as a loss of electrons from the valence shell of the metals, and reduction was defined as the gain of electrons by the valence shell of a nonmetal. The reaction of sodium with chlorine was written as two separate processes, to emphasize the loss of electrons by sodium with the simultaneous gain of electrons by chlorine, as... 

Metals react with nonmetals. These reactions are oxidation-reduction reactions. (See Chapters 4 and 18). Oxidation of the metal occurs in conjunction with reduction of the nonmetal. In most cases, only simple compounds will form. For example, oxygen, 02, reacts with nearly all metals to form oxides (compounds containing O2-). Exceptions are the reaction with sodium where sodium peroxide, Na202, forms and the reaction with potassium, rubidium, and cesium where the superoxides, K02, Rb02, and Cs02 form. 

Chemically, nonmetals are usually the opposite of metals. The nonmetallic nature will increase towards the top of any column and toward the right in any row on the periodic table. Most nonmetal oxides are acid anhydrides. When added to water, they will form acids. A few nonmetals oxides, most notably CO and NO, do not react. Nonmetal oxides that do not react are neutral oxides. The reaction of a nonmetal oxide with water is not an oxidation-reduction reaction. The acid that forms will have the nonmetal in the same oxidation state as in the reacting oxide. The main exception to this is N02, which undergoes an oxidation-reduction (disproportionation) reaction to produce HN03 and NO. When a nonmetal can form more than one oxide, the higher the oxidation number of the nonmetal, the stronger the acid it forms. 

In the first reaction, we have the combination of an active metal with an active nonmetal to form a stable ionic compound. The very active oxygen reacts with hydrogen to form the stable compound water. The hydrogen and potassium are undergoing oxidation, while the oxygen and chlorine are undergoing reduction. 

Bipyridyl (continued) as ligand, 12 135-1% catalysis, 12 157-159 electron-transfer reactions, 12 153-157 formation, dissociation, and racemization of complexes, 12 149-152 kinetic studies, 12 149-159 metal complexes with, in normal oxidation states, 12 175-189 nonmetal complexes with, 12 173-175 oxidation-reduction potentials, 12 144-147... 

In combination reactions, two substances, either elements or compounds, react to produce a single compotmd. One type of combination reaction involves two elements. Most metals react with most nonmetals to form ionic compounds. The products can be predicted from the charges expected for cations of the metal and anions of the nonmetal. For example, the product of the reaction between aluminum and bromine can be predicted from the following charges 3-1- for aluminum ion and 1— for bromide ion. Since there is a change in the oxidation numbers of the elements, this type of reaction is an oxidation-reduction reaction ... 

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