F-block elements

The internal transition elements or block f elements (because they have their valence electrons in the f orbital) are two series, one starting from the lanthanum element and the other from actinium, and for this reason the elements of these series are called lanthanides and actinides. Although in the periodic table of the elements they would have to be after those two elements, they are usually represented separately from the rest. Lanthanides are also known as rare earths. These elements belong to group IIIB or simply to group 3.

They have two electrons (s) in their outermost energy levels (n) and electrons (f) in innermost energy levels (< i>n-2). Some also have electrons (d) in intermediate levels (n-1). See electronic configuration.