Chemistry of Actinoids
The series involving the filling of 5f-orbitals is called actinoids series. It follows actinium, Ac (Z-89) and the elements presents in the series are called actinoids. They include the elements form thorium, Th (Z-90) to lawrencium, Lw (Z-103). As in case of lanthanoids, the name of the series is after the preceding element actinium with which these elements closely resemble. This series also consist of 14 elements.
General characterstics of Actinoids:-
- The melting and boiling points of actinoids are moderately high but they are considerably lower than those of transition elements.
- The densities of actinoids first increase than decrease.
- Actinoids show different oxidation state such as +2, +3, +4, +5, +6 and +7. However +3 oxidation state is most common among all the actinoids.
- Like lanthanoids, actinoids also show actinoids contraction. The size of the atoms or ions of actinoids decrease regularly along the series with the increase in atomic number from actinium to lawrencium. This steady decrease in the ionic radii with the increase in atomic number is called actinoid contraction.
- Most of the actinoid ions are paramagnetic because they contain unpaired electrons.
- Actinoids ions are generally coloured.
- The actinoid metals are all silvery in appearance & display a variety of structures.
- These are highly reactive metals especially in finally divided form.