Which one of the following is an electronic configuration of thorium?

Options

A. `[Rn] 5f^(2) 6 d^(0) 7 s^(2)`
B. `[Rn] 5f^(1) 6 d^(1) 7 s^(2)`
C. `[Rn] 5f^(0) 6 d^(2) 7 s^(2)`
D. `[Rn] 5f^(2) 6 d^(2) 7 s^(2)`

Explanation

To determine the electronic configuration of thorium (Th), we follow these steps:

### Step 1: Identify the Atomic Number
Thorium has an atomic number of 90. This means it has 90 electrons.

### Step 2: Write the Electronic Configuration
We will write the electronic configuration by filling the orbitals according to the Aufbau principle, Hund's rule, and the Pauli exclusion principle.

1. **1s Orbital**: 2 electrons → 1s²
2. **2s Orbital**: 2 electrons → 2s²
3. **2p Orbital**: 6 electrons → 2p⁶
4. **3s Orbital**: 2 electrons → 3s²
5. **3p Orbital**: 6 electrons → 3p⁶
6. **4s Orbital**: 2 electrons → 4s²
7. **3d Orbital**: 10 electrons → 3d¹⁰
8. **4p Orbital**: 6 electrons → 4p⁶
9. **5s Orbital**: 2 electrons → 5s²
10. **4d Orbital**: 10 electrons → 4d¹⁰
11. **5p Orbital**: 6 electrons → 5p⁶
12. **6s Orbital**: 2 electrons → 6s²
13. **4f Orbital**: 14 electrons → 4f¹⁴
14. **5d Orbital**: 10 electrons → 5d¹⁰
15. **6p Orbital**: 6 electrons → 6p⁶
16. **5f Orbital**: 2 electrons → 5f²
17. **6d Orbital**: 0 electrons → 6d⁰
18. **7s Orbital**: 2 electrons → 7s²

Combining all these, the electronic configuration of thorium can be summarized as:
\[ \text{Th: } [Rn] 5f^2 6d^0 7s^2 \]

### Step 3: Determine Stability
While the configuration \( 5f^2 6d^0 7s^2 \) is valid, we also consider the stability of the orbitals. The 5f and 6d orbitals have similar energy levels, but the 5f orbital is more stable than the 6d orbital. Therefore, electrons prefer to occupy the 5f orbital first.

### Step 4: Identify the Correct Option
From the options provided, we confirm that the correct electronic configuration for thorium is:
\[ \text{C: } [Rn] 5f^2 6d^0 7s^2 \]

### Final Answer
The electronic configuration of thorium is:
\[ \text{C: } [Rn] 5f^2 6d^0 7s^2 \]

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