1.

What are f-block elements? Distinguish between lanthanoids and actinoids.

Answer»

a. The elements in which the last electron enters into (n-2) f-orbital of the atoms are called f-block elements.

b. 

LanthanoidsActinoids
1.In lanthanoids, last differentiating electron occupies 4f orbital.In actinoids, last differentiating electron occupies 5f orbital.
2.They are the elements of first inner transition series.They are the elements of second inner transition series.
3.They are present in period 6.They are present in period 7.
4.Most of lanthanoids (with exception of promethium) occur in nature.Most of actinoids (with exception of uranium and thorium) are prepared in laboratory.
5.Most of lanthanoids (with exception of promethium) are non-radioactive.All the actinoids are radioactive.
6.Lanthanoids do not form oxo cation.Actinoids form oxo cation such as \(UO^{2+}_2\)2, PuO2+, UO+.
7.4f orbitals in lanthanoids have higher binding energy.5f orbitals in actinoids have lower binding energy.
8.Contraction in atomic and ionic radii is relatively less in lanthanoids.Contraction in atomic and ionic radii is relatively greater in actinoids due to poor shielding of 5f electrons.
9.Lanthanoids show +2, +3 and +4 oxidation states.Actinoids show +3, +4, +5, +6, +7 oxidation states.
10.Lanthanoids have less tendency to form complexes.Actinoids have greater tendency to form complexes.
11.Some ions of lanthanoids are coloured.Most of the ions of actinoids are deeply coloured.
12.Lanthanoid hydroxides are less basic in nature.Actinoid hydroxides are more basic in nature.


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