Question

Give any two points of difference between lanthanoids and actinoids.

Answer 1

Hint: Lanthanides and the actinides are the elements belonging to the category of the f-block elements and can be easily distinguishable on the basis of their oxidation states in their compounds and the lanthanide contraction (steady decrease in the ionic radii with increase in the atomic radius). Now differentiate between them.

Complete answer:
Lanthanides and actinides both belong to the family of f-block elements. In f-block elements, the elements involve the filling of f-orbitals i.e. in which the last electron enters the last but two i.e.(n-2) f-subshell of the atom. Their general electronic configuration is: $\text{(n-2)} {{\text{f}} ^ {1-14}} \text{(n-1)} {{\text{d}} ^ {0-1}} \text{n}{{\text{s}} ^ {2}}$. They are also called inner transition elements because they are occurring in between the transition elements.
f-block elements occur in two series: lanthanides and actinides. In lanthanides, the 4f subshell is progressively being filled. It consists of 14 elements from Ce (58) to Lu (71) after La (57) and their general electronic configuration is: $\text{4}{{\text{f}}^{1-14}}\text{5}{{\text{d}}^{0-1}}\text{6}{{\text{s}}^{2}}$. On the other hand, in cases of actinides, the 5f subshell is progressively being filled. It also consists of 14 elements from Th (90) to Lr (103) after Ac (89) and their general electronic configuration is: $\text{5}{{\text{f}}^{1-14}}\text{6}{{\text{d}}^{0-1}}\text{7}{{\text{s}}^{2}}$.
Now, we will differentiate between the lanthanide and actinide.

S.no	On the basis of	Lanthanide	Actinide
1.	Oxidation states	They mostly show +3 oxidation states in their compounds except in few they show +2 and +4 oxidation states also.	In addition to +3 oxidation states, they also show +4, +5, +6, +7 oxidation states in their compounds.
2.	Lanthanide contraction	In this, due to the poor shielding effect of the 4s electrons, the contraction in the size is less.	In this, the 5s electrons show more poor shielding effect than the 4s electrons but the shielding effect is not so much poor in its consecutive members and thus, the size decreases to the larger extent in it than the lanthanides.

So, it’s easy to differentiate the metals and non- metals in the tabular form rather than in the paragraph form.

Note:
Lanthanide and the actinide contraction may be defined as the steady decrease in the ionic radii with the increase in the atomic number i.e. the nuclear charge increases as we move from left to right but the electrons are also added in the n-2 subshell and the effect of increased nuclear charge dominates over the imperfect shielding by the 4f and 5f electrons of the lanthanides and the actinides and thus, there is decrease in their ionic radii.