In this paper we present relativistic core ab initio model potentials based on atomic Cowan–Griffin calculations, together with Wood–Boring spin-orbit operators and optimized Gaussian valence basis sets, for the lanthanide elements Ce to Lu and for the actinide elements Th to Lr. This completes the chemically relevant part of the Periodic Table. A [Kr,4d] core was chosen for Ce–Lu and a [Xe,4f,5d] core was chosen for Th–Lr. Minimal (14s10p9d8f )/[2s1p1d1f] and (14s10p11d9f )/[2s1p1d1f] valence basis sets were, respectively, optimized for Ce–Lu and Th–Lr, and a [6s5p5d4f] contraction is recommended for all these 28 elements in molecular calculations. The atomic and molecular results show the same good quality already observed for the main-group elements and the transition metal elements.