What is lanthanoid contraction? What are the consequences of lanthanoid contraction?
In the 6th period, as we move across the period, we find lanthanum and from there the series is separately written as f-block because of the f-subshell. Lanthanides are the elements in f-block from Lanthanum atomic no. 57 (La) to Lutetium atomic no. 71 (Lu). Strength of Shielding Effect of orbitals: On moving from left to right, the nuclear charge increases. This increase is compensated by the increase in the shielding effect by the 4f-electrons. Since the shielding effect of the 4f-electrons is very poor, the atomic and ionic radii undergo a noticeable decrease from left to right. Lanthanoid contraction can be defined as the decrease in the ionic size of the elements while moving across the lanthanide series. Consequences of Lanthanoid Contraction: Due to the highly similar properties, lanthanides are difficult to separate.There is a corresponding increase in the covalent character of the M-OH bond due to the decrease in the size of the M3+ ions. Therefore, the basic character of oxides decreases from left to right. Variation is observed in the physical properties like melting point, boiling point and hardness. Lanthanide contraction is responsible for the slight increase in the standard reduction potential across the series. .
