Chemical bonding, force analysis

Most solid sorbents rely on vapors being sorbed by a physical adsorption mechanism the substance enters the internal pores of the sorbent and is held there by attractive forces considerably weaker and less specific than those of chemical bonds. These weakly attractive forces facilitate desorption for subsequent analysis. The mechanisms for physical adsorption have been studied extensively and are described mathematically by equations such as the Langmuir isotherm. 

Chemical bonds and population analysis Most metals of interest in the context of polymer-based electronic devices form some kind of chemical bond to the polymer upon interaction with a polymer surface. Population analysis, based on the electronic structure, is used to determine the character of this bond. According to the commonly used chemical terminology, bonds are classified as ionic if the bonded atoms are oppositely charged and held together by the attractive Coulomb force, and covalent if the two atoms are neutral but share the same pair of electrons. In the latter case, much of the electron density is located between the bonded atoms whereas for the ionic bond the charge density is concentrated at the atomic sites. 

Table 6 presents a list of the force constants k of some M—X bonds which are calculated by means of normal coordinate analysis, for example89,90. The k values characterize the curvature of the potential well close to the equilibrium intemuclear distance. It is widely believed that the higher the value of k, the stronger the corresponding chemical bond. Such a relation is found in narrow series of isostructural compounds. It follows particularly from the k values of H4- MX , where M = C, Si, Ge X = F, Cl, Br, I n = 1-390. 

If chemical bonding is considered to be too short range to account for possible interactions between CS planes we must look for other interactions which persist over longer distances in the solid. The two which come to mind are electrical interactions, such as electrostatic forces, and physical interactions, such as elastic strain. Both of these are amenable to theoretical analysis, and in the last two years a number of papers concerning these analyses has appeared in the literature. We will summarize the results so far obtained in the Sections below. 

Chemistry always had its own identity, founded in part on analysis and synthesis, in another part on an immense practical exploration of reactions, of chemical change leading to new substances. That distinctly chemical identity persisted as the molecular science became quantitative, and contiguous, so to speak, with physics. Sharing with physics the common ground of atoms, physical forces, and thermod)mamics, chemistry remains different, in its emphasis on structure, reactivity and that marvelous construct of the chemical bond. 

Chemistry has a knack of using terms such as valency, electronegativity and bonding which have a multiplicity of meanings. In its broadest sense, valency has been used to describe the ability of elements to combine with others. Russell s book provides a thorough analysis of the history of valency [15]. A chemical bond is more precisely defined as the force which holds two chemical entities together, but the definition encompasses a duality which at its extremes is based on either electrostatic (ionic) or covalent bonding and in between a variable amount of covalent and ionic character. 

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