Actinoids: 5f orbitals and radioactive character (5f less shielded than 4f → more extension; actinoids radioactive; variable OS more than)
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5f less shielded than 4f → more extension; actinoids radioactive; variable OS more than lanthanoids
When to use this
Early actinoids (Th–U) show higher OS variability; nuclear instability dominates chemical handling.