Because the outer electrons are less
firmly held, they are available for bonding in the actinoids A comparison of the actinoids with the lanthanoids, with respect to
different characteristics as discussed above, reveals that behaviour similar
to that of the lanthanoids is not evident until the second half of the
actinoid series However, even the early actinoids resemble the lanthanoids
in showing close similarities with each other and in gradual variation in
properties which do not entail change in oxidation state The lanthanoid
and actinoid contractions, have extended effects on the sizes, and
therefore, the properties of the elements succeeding them in their
respective periods