An Overview of Chemical Bonding

This chapter deals with the periodicity of the valencies and oxidation states of the elements. An overview of chemical bonding is included to aid in the understanding of the periodicities of the enthalpies of atomization of the elements, and the nature and properties of their fluorides and oxides, which are the subjects of Chapters 6 and 7. 

The details of chemical bonding are left to other books in this series, but it is useful in this text to summarize the main features of the ways in which atoms can bond to each other in elementary forms and in compounds. In the pure elements, the bonding may be described as either metallic or covalent, with small covalent molecules held together by van der Waais intermolecuiar forces in their liquid and solid states. In addition, because compounds are discussed at some length in subsequent chapters, the basis of ionic bonding is described. 

As atomic orbitals are labelled s, p and d, molecular orbitals are labelled a, n and 5, depending on the type of overlap between the atomic orbitals from which they are constructed. 

For example, the bonding in the dinitrogen molecule can be considered to consist of one G bond and two n bonds, giving an overall bond order of three i.e. it can be thought of as a triple bond. 

This occurs in elements which exist in the metallic state, with each atom surrounded by more neighbours than it has electrons available to form electron-pair bonds. To maximize the bonding effect of the valency electrons, they occupy bands of molecular orbitals which extend throughout the metal and allow good electrical conduction to occur. Such bonding can only operate in the solid and liquid states when each atom has sufficient neighbours to allow the delocalization of the electrons into the bands. 

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To be more specific. Chapter 2 provides an overview of Chemically Bonded Phosphate Ceramics. It is intended to streamline the earlier literature and present it in a suitable context. Since the many potential applications of CBPCs are likely to alfect the raw materials (such as phosphates) market, an overview of the raw materials, their general properties, and their manufacturing processes is given in the third chapter. Chapters 4-7 are devoted to the theoretical basis for formation of phosphate ceramics by chemical reactions, and much of the discussion in these chapters is based on thermodynamics. 

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