Lanthanides and Actinides are two prominent families of the periodic table of elements. Discussed below are the differences between the elements in these two families, and their common properties.

Why are the Lanthanide and Actinide Series Separated from the Periodic Table

Lanthanide and actinide are separated from the main body of the periodic table because of how electrons get filled up. They belong to the category of f-bock elements in which the f shell is progressively filled as electrons are added to the atoms. The properties of these elements differ from d-block and s-block. Another reason for placing them below the main body is that they fill up too much space and for simplicity of printing on a standard letter size paper.

Differences and Similarities between Lanthanides and Actinides
What are the Differences
Lanthanides	Actinides
Rare-earth elements	Not rare-earth elements
Reasonably abundant in the surface of the earth	Synthesized in the laboratory (except uranium, thorium)
4f shell filled progressively	5f shell filled progressively.
Non-radioactive (except promethium)	Radioactive
Do not form oxocations	Form oxocation
Form compounds that are low in basicity	Form compounds that are high in basicity
Have a low tendency to form complexes with ligands	Have a high tendency to form complexes with ligands
Colorless	Most ions are colored
Display maximum oxidation state of +4	Display maximum oxidation states of +6
What Do They Have in Common
Belong to the family of inner transitional metals
Have their f shell filled progressively by electrons
Have a common oxidation state of +3
Show contraction in their atomic radii
Highly electropositive and highly reactive

Why Actinides Have Greater Tendency to form Complexes than Lanthanides

Actinides have a greater tendency to form complexes than lanthanides because their ions are smaller and have a large concentration of charges. Therefore, actinides have high nuclear density than lanthanides. Besides, the 4f orbitals in the Ln³⁺ ion do not participate directly in bonding since the 5s² and 5p⁶ orbitals shield it entirely.

References:

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