Question

The common stable oxidation states of Eu and Gd are respectively

• A. +3 and +3
• B. +3 and +2
• C. +2 and +3
• D. +2 and +2

Hint:

Using a simple frame or just bolding for the box Key Points: The most common oxidation state for lanthanides is +3. Extra stability is associated with empty (f$^0$), half-filled (f$^7$), and fully-filled (f$^{14$) f-subshells. Eu ([Xe] 4f$^7$ 6s$^2$) readily forms Eu$^{2+$ ([Xe] 4f$^7$), making +2 a common stable state for Eu. Gd ([Xe] 4f$^7$ 5d$^1$ 6s$^2$) readily forms Gd$^{3+$ ([Xe] 4f$^7$), making +3 the very stable and common state for Gd.

Answer 1

The Correct Option is C

The most common oxidation state for all lanthanides is +3. However, certain lanthanides exhibit other stable oxidation states due to the extra stability associated with empty, half-filled, or completely filled f-subshells.

• Europium (Eu): Atomic Number = 63. Electronic Configuration: [Xe] 4f⁷ 6s².
  • Losing the two 6s electrons gives Eu²⁺ with configuration [Xe] 4f⁷. This is a stable half-filled f-subshell (f⁷). Thus, +2 is a relatively stable and common oxidation state for Europium.
    
  • Losing the two 6s electrons and one 4f electron gives Eu³⁺ with configuration [Xe] 4f⁶. This is the typical +3 state for lanthanides.
  Due to the stability of the f⁷ configuration, Eu readily forms the +2 state. Therefore, its common stable states are +2 and +3, with +2 being notably stable compared to many other lanthanides.
• Gadolinium (Gd): Atomic Number = 64. Electronic Configuration: [Xe] 4f⁷ 5d¹ 6s².
  • Losing the two 6s electrons and the one 5d electron gives Gd³⁺ with configuration [Xe] 4f⁷. This achieves the stable half-filled f-subshell.
    
  • Forming Gd²⁺ ([Xe] 4f⁷ 5d¹) would involve losing only the 6s electrons, which does not result in as stable an f-electron configuration for the ion as Gd³⁺.
  The strong driving force to achieve the stable half-filled f⁷ configuration makes +3 the predominant and most stable oxidation state for Gadolinium.

Comparing the common stable states: Europium commonly shows +2 (due to stable Eu²⁺) in addition to +3, while Gadolinium strongly prefers +3 (due to stable Gd³⁺). Therefore, the respective common stable oxidation states are +2 for Eu and +3 for Gd.