Electropositive substances

Stahls view of the cause of chemical reactions had a very respectable antiquity. He relied on the doctrine of affinities, which traditionally meant the chemical attraction of like for like. It was only later that affinity came to mean the chemical attraction of opposites, for example, of acids for alkalis or, in the nineteenth century, of electronegative for electropositive substances (see Chapter 7). Metals could form alloys, often regarded by chemists as mixts or compounds, by virtue of their shared metallic character. Metals could be dissolved in acids because acids and metals had something in common, some shared principle. That was far from apparent, and it was up to chemists to demonstrate that it was true. Chemists would use the methods and tools of analysis to identify the constituents of mixts. 

Lithium —The neutral atom is monovalent and on the loss of one electron the zerovalent singly charged positive ion Li+ is formed. The formation of a negative ion Li" is theoretically possible, this would have the electronic configuration 1 252 and would thus be zerovalent. Such an ion could only be of importance in compounds with more electropositive substances e,g. LiCs, but in molecules such as lithium hydride the contribution to the resonance of the molecule of the form Li" may be considered as negligible. 

If a buried steel pipeline (Figure 20.17) is connected to an active metal (that is, a highly electropositive substance) such as magnesium, a voltaic cell is formed the active metal is the anode and iron becomes the cathode. Wet soil forms the electrolyte, and the electrode reactions are... 

This description would assign to the caesium atom in the caesium fluoride crystal a resultant charge + and to the fluorine atom a charge — It has seemed to me likely that in general all of the atoms in the complexes that constitute stable chemical substances have resultant electrical charges smaller than those shown by these most electropositive and electronegative atoms in their compounds with one another, and I have accordingly formulated the postulate of the essential electrical neutrality of atoms namely, that the electronic structure of substances is... 

UV/VIS spectrophotometry can be used to determine many physico-chemical characteristics of compounds and thus can provide information as to the identity of a particular compound. Although UV/VIS spectra do not enable absolute identification of an unknown, they are frequently used to confirm the identity of a substance through comparison of the measured spectrum with a reference spectrum. However, UV spectrophotometry is not highly specific, and can obviously only be applied to polymer additives which are absorbers of UV radiation, i.e. contain chromophoric groups. Both UV and IR monitor functional entities rather than the entire molecular structure. A functional group s proximity to other electropositive or electronegative structures in a molecule affects the absorbance spectrum, allowing one to infer some details of molecular structure. 

Combination with oxygen. On the basis of the electronic theory of valency the meaning of the term has been extended to include all reactions in which there occurs an increase in the ratio of the electronegative to the electropositive atoms or groups of a substance. The controlled oxidation of natural rubber produces resinous substances called Rubbones. 

Reducing agent Hydrogen is electropositive when it provides electrons to other substances in chemical reactions and, thus, is a reducing agent. Reduction is the opposite of oxidation. 

Hydroxide anion or OH . This anion is the conjugate base of water. For electropositive elements such as sodium, potassium, and barium, discrete OH ions exist. For such hydroxides, the substance will act as a strong base when dissolved in water thus, M+OH... 

I. Inorganic sulfur compounds containing another (usually more electropositive) element. When the other element is an alkali or alkaline earth, the sulfide is ionic in character. Metal sulfides often have unusual stoichiometries. Examples of sulfides include H2S, Na2S, FeS, and HgS. 2. Organic sulfides are also referred to as thioethers and have the general structure R—S—R. Biochemical examples of sulfides include methionine, cystathionine, and djenkolic acid. If the two R groups are identical, the substance can be referred to as a symmetrical sulfide (biological examples of which are lanthionine and homo-lanthionine). 

Another example that can be handled by ordinary methods of chemical equilibrium is the equilibrium between an ion and a neutral atom of another substance, in which the more electropositive atom is the one forming the positive ion, in equilibrium. Thus, consider the reaction Li + Ne+ <= Li+ + Ne, in which Li has a much smaller ionization potential than Ne, or is more electropositive. The equilibrium will be given... 

Silicon is the most plentiful electropositive element on the earth s crust, being three times as abundant as aluminum and six times as abundant as iron. Yet the only compounds of silicon which have been important to human history are those natural forms of silica and the silicate minerals which are used in the building arts and in ceramic technology. Only within the past 90 years have hydrides and organic derivatives of silicon been synthesized, and the chlorides 30 years before up to a few years ago it could be said that all these substances were still relatively unknown products of the laboratory, unimportant save for their scientific interest. The chemistry and technology of silicon continued to be dominated entirely by consideration of the inorganic silicates. 

The sixth in the periodic table of elements is, at the same time, among the most important ones. With about 180 ppm, carbon is only 17th on the list of terrestrial elements frequency, situated even after barium or sulfur-for comparison, the second-most frequent element, silicon, is about 1300 times as abundant as carbon. Still the latter is essential for the assembly of all organic matter. It is predestined for this central role especially due to its mid position in the periodic system and its associated ability to form stable substances with more electropositive and more electronegative reaction partners. Yet in the present text the organic chemistry resulting from these various bonding possibilities will only be mentioned if it is employed to modify carbon materials or, to put it in other words, the element itself as a material will be in the focus. 

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