The f-block of the periodic table of elements consists of those elements (sometimes referred to as the inner transition elements) for which, in the atomic ground state, the highest-energy electrons occupy f-orbitals. Unlike the other blocks, the conventional divisions of the f-block follow periods of similar atomic number rather than groups of similar electron configuration. Thus, the f-block is divided into the lanthanide series and the actinide series.
The name 'inner transition' is derived by analogy with the transition metals.
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