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The F-block Elements

f- Block Elements

The f-block elements or inner transition elements are those in which the last electron enters any one out of seven f-orbitals of their respective ante-penultimate shells. These elements have electrons (1 to 14) in the f orbital, (0 to 1) in the penultimate energy level’s d orbital, and (0 to 1) in the outermost orbital. In the f-block, there are primarily two series that correspond to the filling of 4f and 5f orbitals. The elements are divided into two groups: the 4f series of Ce to Lu and the 5f series of Th to Lw. Each series contains 14 elements that fill the ‘f’ orbital.


Inner transition elements are typically members of Group 3, but they can also be viewed separately as f block elements. The 4f and 5f orbitals are filled in the f-block elements. The f-block elements are the inner transition elements. These metal elements provide a transition in the sixth and seventh rows of the periodic table, separating the s block and the d block elements.

The F-block elements are classified into two series- lanthanides and actinoids.

Properties of Lanthanides

Lanthanide or lanthanoid chemical elements are a group of 15 metallic chemical elements with atomic numbers 57-71, ranging from lanthanum to lutetium.

Properties of Actinides

The actinide or actinoid series includes the 15 metallic chemical elements actinium through lawrencium with atomic numbers ranging from 89 to 103. The name actinide comes from the first element in the series, actinium.

The atomic radius decreases with the series as a result of actinoid contraction. This contraction occurs as a result of the 5f orbitals‘ poor shielding. As a result, the outermost electron is affected by the positive nuclear charge, which reduces the atomic radius and the actinide series.

The most common oxidation state shown by actinoids is +3 (but this is not always stable). The metals in the actinides series are highly reactive.


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