Question

question 4 (5 points)
which of the following statements explains the cause of lanthanide contraction?
a) protons exhibit a stronger pull on outer f orbitals than on d orbitals.
b) the d orbitals in actinides have paired electrons.
c) the d orbitals in lanthanides have unpaired electrons.
d) all lanthanides and actinides are radioactive.

Explanation:

To determine the cause of lanthanide contraction, we analyze each option:

• Option A: Lanthanide contraction occurs because as protons are added in the nucleus, the f - orbitals (which are less effective at shielding the nuclear charge compared to d - orbitals) lead to a stronger pull on the outer electrons by the nucleus. So protons have a stronger pull on outer f - orbitals than d - orbitals, which explains lanthanide contraction.
• Option B: The d - orbitals in actinides are not related to the cause of lanthanide contraction (lanthanides involve f - orbitals, and actinides are a different series). Also, this statement is not relevant to the cause of lanthanide contraction.
• Option C: The presence of unpaired electrons in d - orbitals of lanthanides does not explain the lanthanide contraction. Lanthanide contraction is related to the shielding effect of f - orbitals.
• Option D: Radioactivity of lanthanides and actinides has nothing to do with the cause of lanthanide contraction.

Answer:

A. Protons exhibit a stronger pull on outer \( f \) orbitals than on \( d \) orbitals.