Lanthanoid ions with \(4f^7\) configuration are:
(A) Eu\(^{2+}\) (B) Gd\(^{3+}\) (C) Eu\(^{3+}\) (D) Tb\(^{3+}\) (E) Sm\(^{2+}\)
Choose the correct answer from the options given below:
Show Hint
- (A) and (B) only
- (A) and (D) only
- (B) and (E) only
- (B) and (C) only
The Correct Option is A
Approach Solution - 1
Step 1: Write the electronic configurations.
\(_{63}\)Eu\(^{2+}\) - [Xe] 4f\(^7\) 6s\(^0\)
\(_{64}\)Gd\(^{3+}\) - [Xe] 4f\(^7\) 5d\(^0\) 6s\(^0\)
\(_{63}\)Eu\(^{3+}\) - [Xe] 4f\(^6\) 6s\(^0\)
\(_{65}\)Tb\(^{3+}\) - [Xe] 4f\(^8\) 6s\(^0\)
\(_{62}\)Sm\(^{2+}\) - [Xe] 4f\(^6\) 6s\(^0\)
Step 2: Identify the ions with 4f\(^7\) configuration.
From the electronic configurations, we can see that Eu\(^{2+}\) and Gd\(^{3+}\) have 4f\(^7\) configurations.
Step 3: Select the correct option.
Therefore, the correct answer is (A) and (B) only.
Approach Solution -2
Step 1 — Recall the general electronic configuration of lanthanoids:
The general configuration of lanthanoids is: \[ [\text{Xe}]\,4f^{1-14}\,5d^{0-1}\,6s^2 \]
Step 2 — Determine the \(4f\) configuration for each ion:
- (A) Eu\(^{2+}\)
Neutral Eu: [Xe] 4f7 6s2
After losing 2 electrons → Eu\(^{2+}\): [Xe] 4f7
✅ Has \(4f^7\) configuration. - (B) Gd\(^{3+}\)
Neutral Gd: [Xe] 4f7 5d1 6s2
After losing 3 electrons → Gd\(^{3+}\): [Xe] 4f7
✅ Has \(4f^7\) configuration. - (C) Eu\(^{3+}\)
Eu\(^{3+}\): [Xe] 4f6 ❌ (not 4f7) - (D) Tb\(^{3+}\)
Tb\(^{3+}\): [Xe] 4f8 ❌ (not 4f7) - (E) Sm\(^{2+}\)
Sm\(^{2+}\): [Xe] 4f6 ❌ (not 4f7)
Step 3 — Correct pair:
The ions with \(4f^7\) configuration are Eu\(^{2+}\) and Gd\(^{3+}\).
Final Answer:
✅ (A) and (B) only
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