Valence states and nature of f-electrons in f-systems

The Mott-Hubbard theory of localized versus itinerant electron behaviour is applied semi-quantitatively to the 5f electrons in the actinides. Especially, the Hill plot is discussed from this point of view. The concept of valence is used exclusively for systems where the 5f electrons are localized. From a thermodynamical analysis, it is shown that the valence picture is not applicable to the earlier actinide metals. Instead, the 5f electrons must be considered as itinerant electrons. Also various other examples are given, where thermodynamical data can provide considerable insight into the basic electronic structure of f-systems. (author)