General Properties of Actinide Series (5f block elements)
In 1923 Neils Bohr postulated the existence of an actinide series analogous to the lanthanide series. The fifteen elements from actinium to lawrencium constitute the actinide series of the periodic table.
The general electronic configuration of actinides is [Rn] 5f0,1-14 6d0,1-2 7s2 where Rn stands for radon core.
These elements show the oxidation states of +2, +3, +4, +5 and +6. Out of these, +4 oxidation state is the most common state.
Radii of M3+ and M4+ ions
The ionic radii of actinide elements decrease gradually as we move along the actinide series. The steady decrease in the ionic radii with an increase in nuclear charge is called actinide contraction and is analogous to lanthanide contraction.