Lanthanoid contraction is the accumulation of successive shrinkages.

As a result of lanthanoid contraction, the properties of 4d series of the transition elements have no similarities with the 5d series of elements.

Shielding power of 4$$f$$ electrons is quite weak.

There is a decrease in the radii of the atoms or ions as one proceeds from La to Lu.

Ni²⁺, Cu⁺

Ni²⁺, Ti³⁺

Sc³⁺, Ti³⁺

Sc³⁺, Co²⁺.

more active nature of the actinoids

more energy difference between 5f and 6d orbitals than that between 4f and 5d orbitals

lesser energy difference between 5f and 6d orbitals than that between 4f and 5d orbitals

greater metallic character of the lanthanoids than that of the corresponding actinoids.

Cu(CN)₂

CuCN

[Cu(CN)₄]^3$$-$$

[Cu(CN)₄]^2$$-$$