Question

What is the lanthanide contraction? How does the lanthanide contraction affect the properties of the 4d and 5d transition metals?

Short answer

Lanthanide contraction is the gradual decrease in size of atoms with increasing atomic number.

Step-by-step solution

Lanthanides  

Lanthanides are the series of elements with atomic number 58 to 71. It starts from Lanthanum from which it got this name. The atomic size of the lanthanide steadily decreases from Lanthanum to Lutetium since the nuclear charge increases. Atomic radii and ionic radii both depends on nuclear charge. With increase in nuclear charge the atomic and ionic radii decreases because of the greater attraction between electron and nucleus.

The lanthanide contraction

The lanthanide contraction affects the chemistry of 4d and 5d transition metals. Both 4d and 5d transition metals have similar atomic radii due to lanthanide contraction. There is a general decrease of base strength from Lanthanum to Lutetium. The co-valency of the metals increases going from left to right. They have higher ionization energy.