Question

For how many of the following elements, in the process of M → M3+ , the number of f-electrons remains unchanged. Pm (61) , Eu (63) , Gd (64) , Dy (66) , Ce (58) , Lu (71) , Th (90) , U (92) , Pu (94)

Answer 1

5

Answer 2

To determine the number of elements for which the number of f-electrons remains unchanged during the process M $\rightarrow$ M$^{3+}$, we need to find the ground state electronic configuration of each element (M) and its corresponding M$^{3+}$ ion. Electrons are removed from the outermost shell first during ionization. For f-block elements, the order of removal is generally ns, then (n-1)d, and finally (n-2)f.

Let's examine each element:

1. Pm (Z=61):

   Ground state configuration (M): [Xe] $4f^5 6s^2$. Number of f-electrons = 5. M$^{3+}$ ion: Remove 2 electrons from 6s and 1 electron from 4f. Configuration (M$^{3+}$): [Xe] $4f^4$. Number of f-electrons = 4. Change in f-electrons: Yes (5 $\rightarrow$ 4).

2. Eu (Z=63):

   Ground state configuration (M): [Xe] $4f^7 6s^2$. Number of f-electrons = 7. M$^{3+}$ ion: Remove 2 electrons from 6s and 1 electron from 4f. Configuration (M$^{3+}$): [Xe] $4f^6$. Number of f-electrons = 6. Change in f-electrons: Yes (7 $\rightarrow$ 6).

3. Gd (Z=64):

   Ground state configuration (M): [Xe] $4f^7 5d^1 6s^2$. Number of f-electrons = 7. M$^{3+}$ ion: Remove 2 electrons from 6s and 1 electron from 5d. Configuration (M$^{3+}$): [Xe] $4f^7$. Number of f-electrons = 7. Change in f-electrons: No (7 $\rightarrow$ 7).

4. Dy (Z=66):

   Ground state configuration (M): [Xe] $4f^{10} 6s^2$. Number of f-electrons = 10. M$^{3+}$ ion: Remove 2 electrons from 6s and 1 electron from 4f. Configuration (M$^{3+}$): [Xe] $4f^9$. Number of f-electrons = 9. Change in f-electrons: Yes (10 $\rightarrow$ 9).

5. Ce (Z=58):

   Ground state configuration (M): [Xe] $4f^1 5d^1 6s^2$. Number of f-electrons = 1. M$^{3+}$ ion: Remove 2 electrons from 6s and 1 electron from 5d. Configuration (M$^{3+}$): [Xe] $4f^1$. Number of f-electrons = 1. Change in f-electrons: No (1 $\rightarrow$ 1).

6. Lu (Z=71):

   Ground state configuration (M): [Xe] $4f^{14} 5d^1 6s^2$. Number of f-electrons = 14. M$^{3+}$ ion: Remove 2 electrons from 6s and 1 electron from 5d. Configuration (M$^{3+}$): [Xe] $4f^{14}$. Number of f-electrons = 14. Change in f-electrons: No (14 $\rightarrow$ 14).

7. Th (Z=90):

   Ground state configuration (M): [Rn] $6d^2 7s^2$ (equivalent to [Rn] $5f^0 6d^2 7s^2$). Number of f-electrons = 0. M$^{3+}$ ion: Remove 2 electrons from 7s and 1 electron from 6d. Configuration (M$^{3+}$): [Rn] $6d^1$ (equivalent to [Rn] $5f^0 6d^1$). Number of f-electrons = 0. Change in f-electrons: No (0 $\rightarrow$ 0).

8. U (Z=92):

   Ground state configuration (M): [Rn] $5f^3 6d^1 7s^2$. Number of f-electrons = 3. M$^{3+}$ ion: Remove 2 electrons from 7s and 1 electron from 6d. Configuration (M$^{3+}$): [Rn] $5f^3$. Number of f-electrons = 3. Change in f-electrons: No (3 $\rightarrow$ 3).

9. Pu (Z=94):

   Ground state configuration (M): [Rn] $5f^6 7s^2$. Number of f-electrons = 6. M$^{3+}$ ion: Remove 2 electrons from 7s and 1 electron from 5f. Configuration (M$^{3+}$): [Rn] $5f^5$. Number of f-electrons = 5. Change in f-electrons: Yes (6 $\rightarrow$ 5).

The elements for which the number of f-electrons remains unchanged are Gd, Ce, Lu, Th, and U. There are 5 such elements.