Appendix: Fundamental concepts: a concise review

Summary

A chemist's approach to understanding matter is conveniently divided into three stages. First, fixed stoichiometric relationships between the atomic constituents of matter exist in molecular compounds and in many compounds with extended structures. Hence, the composition of a pure substance provides initial definition to a new substance. Given the atomic nature of substances, it provides direct information on structure. In a historical sense, other early means of characterization were physical ones, e.g., melting point or dipole moment, and sensual, e.g., color or taste. As a consequence, they are less directly related to structure. In the second stage, geometric relationships between the constituent atoms as well as spectroscopic and theoretical information on electronic structure add dimensions and shape to the composition data. Finally, reaction chemistry, i.e., reaction stoichiometries, rates and mechanisms, provides connections between compound types as well as generating new substances for which the whole process begins again.

Stable compounds are the most thoroughly characterized and provide the corpus of chemistry. However, “stability” is one of the definable, but casually used, terms of chemistry. Stability is associated with energy, and energy and structure are inextricably combined. A chemist, well educated in a given area, has a good understanding of both energy and structure. In a practical sense, stable for the inorganic chemist is often defined empirically by isolation and storage at room temperature. Most stable is often implied by the term, but it is not always clear that the most stable (thermodynamic) products have been characterized in a given reaction.