The concept of chemical periodicity is central to the study of inorganic chemistry. There is no single best form of the periodic table because the choice depends on the purpose for which the table is used. Some forms emphasize chemical relations and valence, whereas others stress the electronic configuration of the elements or the dependence of the periods on the shells and subshells of the atomic structure. This chapter discusses the periodic law in terms of the electronic structure of atoms. It discusses the use of the periodic table and graphs to systematize trends in physical and chemical properties and to detect possible errors, anomalies, and inconsistencies. The chapter also describes the use of the periodic table to predict new elements and compounds and to suggest new areas of research. The most characteristic chemical property of an element is its valence. There are numerous measures of valence, each with its own area of usefulness and applicability. The chapter illustrates the trends in atomic, physical, and chemical properties of the elements in each group and along each period.
