f-electron hybridization and heavy-fermion compounds

Hybridization between f orbitals and non-f ligands on neighboring sites is discussed as the primary mechanism determining the bandwidth and properties of certain Ce and U compounds, including the heavy-fermion metals. The occurrence and systematic variation of heavy-fermion and related behavior in the Periodic Table is interpreted in terms of this hybridization mechanism, with a specific discussion of experimental data for the U$X_3$ compounds. Several experiments are suggested to clarify and extend these ideas.