Question

Compare the chemistry of the actinides with that of lanthanides with reference to: (i) Electronic configuration (ii) Atomic and ionic sizes (iii) Oxidation states and (iv) Chemical reactivity

Answer 1

Hint: The lanthanides have incompletely filled 4f orbital whereas the actinides have incompletely filled 5f orbital. This property will give you some idea about their electronic configurations and atomic and ionic sizes, which you can then use to find out more about their oxidation states and chemical reactivity.

Complete step by step answer:
We will first see basic information about f-block elements to get a better idea.
- F-block elements are those which have incomplete f-orbitals. The sublevel contains seven orbitals, each of which will hold two electrons. Therefore, it is possible to place 14 electrons in the 4f sublevel.
- Let’s see the comparison of lanthanides and actinides in given properties.

Property	Lanthanides	Actinides
Electronic configuration	The lanthanide elements have electron configurations that follow the Aufbau’s rule, and the 4f sublevel is filled as atomic number increases from Cerium to Lutetium .General electronic configuration of lanthanide elements can be given as \[[Xe]4{{f}_{1-14}}5{{d}_{0-1}}6{{s}_{2}}\] .	In actinides, the electrons are filled in incompletely filled 5f orbitals starting from Actinium to Lawrencium (atomic number 89 to 103). General electronic configuration of actinide elements can be given as \[[Rn]5{{f}_{1-14}}6{{d}_{0-1}}7{{s}_{2}}~\]
Atomic and ionic sizes	Starting from Cerium to Lutetium, it has been observed that the size of metal and its ions decrease with increase in atomic number. This occurs because an increase in positive charge in the nucleus contracts the valence orbital of electrons. This order of decreasing atomic and ionic sizes is also called Lanthanide contraction.	In actinides, starting from Actinium to Lawrentium, atomic and ionic size decrease with increase in atomic number as lanthanides. The reason is the same as lanthanides. This phenomenon is called actinide contraction.
Oxidation states	Most of the lanthanide elements show +3 oxidation state while some of the atoms show +2 and +4 oxidation states as well. There is a large energy gap between 4f and 5d orbitals; this is the reason why it does not show more oxidation states.	Actinides have a very small energy gap between 5f and 6d orbitals, so they can easily form a variety of configurations and hence they are found to be stable in various oxidation states.
Chemical reactivity	They are comparatively less electropositive than actinides and due to that reason, they are less reactive than actinides.	They are more electropositive than lanthanides because they are under the lanthanides in periodic tables. So, they are more reactive than lanthanides.

Note: Remember that while all actinides are radioactive in nature, lanthanides are fairly stable in comparison and are found making coordination complexes. Another point of consideration is the differences in size of the two sets of elements, as the contraction observed in the actinide series is not nearly as noticeable as that in the lanthanide elements due to the poor shielding effect of the 5f orbital.