What is lanthanoid contraction? What arc the consequences of lanthahoid contraction?
What is lanthanoid contraction? What arc the consequences of lanthahoid contraction?
Lanthanoid contraction
The overall decrease in atomic and ionic radii from lanthanum to lutetium is observed in the lanthanoids, the increase in nuclear attraction due to the addition of proton is more pronounced than the increase in the interelectronic repulsions due to the addition of the electron. This phenomenon is called lanthanoid contraction. It means every additional proton in the nucleus, the corresponding electron goes into a 4f-subshell. This is too diffused to screen the nucleus as effectively as the more localised inner shell. Hence, the attraction of the nucleus for the outermost electrenSincreases steadily with the atomic number.
Consequences of Lanthanoid Contraction The important consequences of lanthanoid contraction are as follows :
(i) The basic character of oxides and hydroxides Due to the lanthanoid contraction, the covalent nature of La - OH bond increases and thus, the basic character of oxides and hydroxides decreases from La(OH)3 to Lu(OH)3.
(ii) The similarity in the size of elements of second and third transition series Because of lanthanoid contraction, elements which follow the third transition series are considerably smaller than would otherwise be expected. The normal size increases from Sc→Y→La and disappears after lanthanides. Thus, pairs of elements such as Zr/Hf, NO PM and Mo/w are almost identical in size.
Due to almost similar size, such pairs have very similar properties which make their separation difficult.
(iii) Separation of lanthanoids Due to lanthanoid contraction, there is a difference in some properties of lanthanoid like solubility, a degree of hydration and complex formation. These difference enable the separation of lanthanoids by ion exchange method.
Lanthanoid contraction
The overall decrease in atomic and ionic radii from lanthanum to lutetium is observed in the lanthanoids, the increase in nuclear attraction due to the addition of proton is more pronounced than the increase in the interelectronic repulsions due to the addition of the electron. This phenomenon is called lanthanoid contraction. It means every additional proton in the nucleus, the corresponding electron goes into a 4f-subshell. This is too diffused to screen the nucleus as effectively as the more localised inner shell. Hence, the attraction of the nucleus for the outermost electrenSincreases steadily with the atomic number.
Consequences of Lanthanoid Contraction The important consequences of lanthanoid contraction are as follows :
(i) The basic character of oxides and hydroxides Due to the lanthanoid contraction, the covalent nature of La - OH bond increases and thus, the basic character of oxides and hydroxides decreases from La(OH)3 to Lu(OH)3.
(ii) The similarity in the size of elements of second and third transition series Because of lanthanoid contraction, elements which follow the third transition series are considerably smaller than would otherwise be expected. The normal size increases from Sc→Y→La and disappears after lanthanides. Thus, pairs of elements such as Zr/Hf, NO PM and Mo/w are almost identical in size.
Due to almost similar size, such pairs have very similar properties which make their separation difficult.
(iii) Separation of lanthanoids Due to lanthanoid contraction, there is a difference in some properties of lanthanoid like solubility, a degree of hydration and complex formation. These difference enable the separation of lanthanoids by ion exchange method.
