What impact do f orbitals have on shielding in the lanthanides?

In the context of the lanthanides, f orbitals play a significant role in determining the effective nuclear charge experienced by outer electrons. The f orbitals are characterized by their complex shapes and relative distance from the nucleus. As a result, the electrons in these f orbitals do not effectively shield the positive charge of the nucleus from the outer electrons.

This leads to the phenomenon where the outer electrons experience a higher effective nuclear charge because the f electrons, rather than providing a good shielding effect, are insufficient in offsetting the nuclear attraction. Thus, the outer electrons feel a stronger pull from the nucleus than they would if the shielding were more effective. Consequently, this results in a trend within the lanthanide series, where the increase in the effective nuclear charge can impact various properties, such as ionic and atomic sizes, as well as ionization energies.

Understanding the inefficiency of f orbitals in shielding clarifies why the correct answer emphasizes their poor shielding capability and the subsequent influence on the effective nuclear charge.