There is a gradual decrease in the size of atoms or M
3+ ions across the
series This may be referred to as the actinoid contraction (like lanthanoid
contraction) The contraction is, however, greater from element to element
in this series resulting from poor shielding by 5f electrons There is a greater range of oxidation states, which is in part attributed to
the fact that the 5f, 6d and 7s levels are of comparable energies