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Question
Name the members of the lanthanoid series which exhibit +4 oxidation state and those which exhibit +2 oxidation state. Try to correlate this type of behavior with the electronic configurations of these elements.
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Solution 1
The lanthanides that exhibit +2 and +4 states are shown in the given table. The atomic numbers of the elements are given in parentheses.
| +2 | +4 |
| Nd (60) | Ce (58) |
| Sm (62) | Pr (59) |
| Eu (63) | Nd (60) |
| Tm (69) | Tb (65) |
| Yb (70) | Dy (66) |
After forming Ce4+, Ce attains a stable electronic configuration of [Xe].
After forming Tb4+, Tb attains a stable electronic configuration of [Xe] 4f7.
After forming Eu2+, Eu attains a stable electronic configuration of [Xe] 4f7.
After forming Yb2+, Yb attains a stable electronic configuration of [Xe] 4f14.
Solution 2
All lanthanoids show the Ln3+ oxidation state. But some of them also show +2 and +4 states in solution and solid forms, such as Ce4+, Eu2+, Yb2+, Tb4+, etc. The changing oxidation state correlates with electronic configuration owing to the enhanced stability of half-filled, fully filled, or vacant orbitals. e.g., Ce4+ has 4f0, Eu2+ has 4f7, Tb4+ has 4f7, and Yb2+ has 4f14 configuration.
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