SOME ASPECTS OF CHEMICAL BONDING

In this Section, we introduce some new theoretical ideas, which will prove useful in the descriptive chemistry of the non-metals. 

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In this chapter, some aspects of chemical bonding will be discussed. It will be shown that chemical combination corresponds to the tendency of atoms to assume the most stable electron configuration possible. 

This article has been devoted to some aspects of chemical bonding that emerge from the classic key concept of valence. Mathematical formulations have frequently been utilized in order to facilitate precise state ments, so that a brief non-mathematical summary may be called for. 

In this chapter, some aspects of chemical bonding will be discussed. It will be shown that chemical combination corresponds to the tendency of atoms to assume the most stable electronic configuration possible. Before we start to study the forces holding the particles together in a compound, however, we must first understand the meaning of a chemical formula (Sec. 5.2). Next we learn why ionic compounds have the formulas they have, for example, why sodium chloride is NaCl and not NaCl2 or NaCls. 

We outline all the different bonding types that are essential for most chemical bond descriptions on metal surfaces. First, we discuss some general aspects of chemical bonding. In particular, in comparison to the delocalized s- or p-electrons, we emphasize the uniqueness of the more localized d-electrons in transition metals in the formation of the chemical bond. Most of the active catalysts are transition metals where -electrons play a major role and most adsorbates interact with the metal substrate via covalent bonding, i.e., electron-pair sharing involving mainly substrate -electrons. 

Some of the papers comprising the first volume deal with those theoretical and experimental aspects of chemical bonds in crystals which relate to the most general rules governing the dependence of the atomic interactions on the positions of the components in Mendeleevas periodic table. The criteria governing the transitions from the metallic to the semiconducting and the superconducting states are also considered. 

V t J ncum Mechanics for Chemists is designed to provide chemistry undergraduates with a basic understanding of the principles of quantum mechanics. The text assumes some knowledge of chemical bonding and a familiarity with the qualitative aspects of molecular orbitals in molecules such as butadiene and benzene. Thus it is intended to follow a basic course in organic and/or inorganic chemistry. 

We ve now surveyed some important aspects of chemical bonding, and we ve gained an understanding of a number of key concepts. But if we want to think about the connections between bonding and the properties of compounds, we often need to know not just that bonds have formed, but how many bonds have formed and between which elements. The Lewis structures we introduced in Section 7.3 provide a powerful tool for doing this. In drawing Lewis structures for... 

In the remainder of this chapter, we will concentrate, after a few short remarks on some aspects of nomenclature, on the description of syntheses, physical properties, bonding situation, and chemical reactivity of NHP derivatives of the types ID-VIL... 

In this chapter we will not attempt to give an overview of all of the knowledge on the reactivity of chalcogen-donor molecules towards di- and inter-halogens, since some aspects of this are discussed in other chapters. Instead, this chapter is dedicated exclusively to the analysis of the chemical bond and structural features of C.-T. adducts between LE chalcogen-donor molecules (E = S, Se) and di- and inter-halogens, and their reactivity towards metal powders. 

M. N. Paddon-Row, Some Aspects of Orbital Interactions Through Bonds Physical and Chemical Consequences , Acc Chem. Res. 1982,15,245-251. 

The second class includes those elements that form only one chemical bond at a time. These elements terminate some aspect of the molecular structure, since, once they have bonded, there is nowhere else to go. Hydrogen provides an obvious example. We have already encountered three other elements in this class fluorine, chlorine. 

The properties of a compound with isolated double bonds, such as 1,4-pentadiene, generally are similar to those of simple alkenes because the double bonds are essentially isolated from one another by the intervening CH2 group. However, with a conjugated alkadiene, such as 1,3-pentadiene, or a cumulated alkadiene, such as 2,3-pentadiene, the properties are sufficiently different from those of simple alkenes (and from each other) to warrant separate discussion. Some aspects of the effects of conjugation already have been mentioned, such as the influence on spectroscopic properties (see Section 9-9B). The emphasis here will be on the effects of conjugation on chemical properties. The reactions of greatest interest are addition reactions, and this chapter will include various types of addition reactions electrophilic, radical, cycloaddition, and polymerization. 

We start with some biographical notes on Erich Huckel, in the context of which we also mention the merits of Otto Schmidt, the inventor of the free-electron model. The basic assumptions behind the HMO (Huckel Molecular Orbital) model are discussed, and those aspects of this model are reviewed that make it still a powerful tool in Theoretical Chemistry. We ask whether HMO should be regarded as semiempirical or parameter-free. We present closed solutions for special classes of molecules, review the important concept of alternant hydrocarbons and point out how useful perturbation theory within the HMO model is. We then come to bond alternation and the question whether the pi or the sigma bonds are responsible for bond delocalization in benzene and related molecules. Mobius hydrocarbons and diamagnetic ring currents are other topics. We come to optimistic conclusions as to the further role of the HMO model, not as an approximation for the solution of the Schrodinger equation, but as a way towards the understanding of some aspects of the Chemical Bond. 

Introduction.—There have been several reviews of the chemical technology of titanium and its compounds.1-30 The organometallic4 and structural40 chemistry of titanium reported during 1972 has been reviewed as have some aspects of its synthetic chemistry.5 According to ab initio calculations the Ti—C bond in TiCO and TiCO+ can be described as a CO non-bonding pair that is shifted slightly onto the Ti and a shift of Ti 3d n-orbitals back onto the CO.b... 

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