The electronic configuration of chromium (Z=24) is:

Options

A. `[Ne]3s^(2)3p^(6)3d^(4)4s^(2)`
B. `[Ne]3s^(2)3p^(6)3d^(5)4s^(1)`
C. `[Ne]3s^(2)3p^(6)3d^(5)4s^(1)`
D. `[Ne]3s^(2)3p^(6)3d^(1)4s^(2)`

Answer

To determine the electronic configuration of chromium (Z=24), we need to follow these steps:

### Step 1: Understand the Atomic Number
Chromium has an atomic number of 24, which means it has 24 electrons.

### Step 2: Fill the Electron Shells
According to the Aufbau principle, electrons fill orbitals starting from the lowest energy level to the highest. The order of filling is as follows:
1. 1s
2. 2s
3. 2p
4. 3s
5. 3p
6. 4s
7. 3d

### Step 3: Fill the Orbitals
We fill the orbitals in the order mentioned above until we reach 24 electrons:
- 1s² (2 electrons)
- 2s² (2 electrons)
- 2p⁶ (6 electrons)
- 3s² (2 electrons)
- 3p⁶ (6 electrons)
- 4s² (2 electrons)
- 3d⁴ (4 electrons)

At this point, we have filled 2 + 2 + 6 + 2 + 6 + 2 + 4 = 24 electrons, which would suggest an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁴.

### Step 4: Identify the Exception
However, chromium is an exception to the expected filling order. Instead of having 3d⁴ 4s², it adopts a more stable configuration of 3d⁵ 4s¹. This is because half-filled and fully filled subshells are more stable due to electron exchange energy and symmetry.

### Step 5: Write the Final Configuration
Thus, the correct electronic configuration for chromium is:
\[ \text{Cr: } 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 3d⁵ \]

### Conclusion
The electronic configuration of chromium (Z=24) is:
\[ \text{Cr: } [Ar] 4s¹ 3d⁵ \]