# Where are the lanthanides and actinides placed in the periodic table? Why?

Both the lanthanide and actinide metals are LARGE, Lewis-acidic metals, in which the $f$ subshell is progressively filled. The Group 3 metals, scandium, yttrium, and lanthanum, are often considered in this category, because they share similar chemistry.
Given the properties of the $\text{f-orbitals}$ (which are diffuse, and offer poor electronic shielding), the f element metals usually give ${M}^{2 +}$, and ${M}^{3 +}$ oxidation states, and are marked by extreme Lewis acidity. Their chemistry is the province of specialists.