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How does the lanthanide contraction affect the chemical properties of rare-earth elements?
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rare-earth element
Electron probabilities, P2(r), for the 4f, 5s, 5p, 5d, and 6s electrons of gadolinium.
The lanthanide contraction refers to the steady decrease in the atomic and ionic radii of the rare-earth elements as the atomic number increases from lanthanum to lutetium. This phenomenon significantly influences their chemical behavior in the following ways:12
- Chemical Similarity: Because the 4f electrons are "localized" and do not participate directly in chemical bonding, the rare-earth elements generally exhibit a stable +3 oxidation state. The contraction keeps the ionic radii of these elements very similar, which accounts for their extreme chemical resemblance and their tendency to occur together in minerals.12
- Basicity: The lanthanide contraction is responsible for a systematic decrease in basicity as one moves across the series from lanthanum to lutetium.2
- Separation Techniques: The slight, systematic differences in ionic size and basicity resulting from the contraction provide the fundamental basis for various separation and purification techniques, such as ion-exchange processes.32
- Periodic Table Trends: The contraction also explains the striking chemical similarity between zirconium and hafnium, as the latter possesses a nearly identical radius to the former due to the preceding lanthanide series.1