Periodicity of the change in properties in the series of d- and f-elements

Many physicochemical properties in series of d- and f-elements change periodically with change in the number of d- or f-electrons in the d^q- or f^q-electron configurations. In the lanthanide and actinide series for a fixed electron configuration, the f^q-periodicity of the change in properties is called the tetrad or double–double relationship.
A number of properties of d-elements, lanthanides, and actinides depend on the initial d^q-, f^q- and final d^q–1-, f^q–1-electron configurations. These properties include the ionisation potentials of the free atoms and ions, electron affinity, redox potentials, excitation energies, and enthalpies of the decomposition and disproportionation of the halides, oxides, chalcogenides, and pnictides of the lanthanides and actinides, the oxidation state in compounds with variable oxidation states, etc. The present review analyses the regularity of the change in these properties in the lanthanide and actinide series, demonstrates the nature of the change in these properties, formulates a simple rule making it possible to predict unknown properties, and carried out an extensive comparison with the properties of d- and p-elements and their compounds. The properties of the trans-actinide g- and h-elements are predicted.
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