Which of the following is the correct electron configuration for Se
2−
?
A. [Ar] 4s
2
3d
10
4p
6
B. [Ar] 4s
2
3d
10
4p
2
C. [Ar] 4s
2
3d
10
4p
4
D. [Ar] 4s
2
4d
10
4p
6
The Correct Answer and Explanation is :
The correct answer is: A: [Ar] \, 4s^2 \, 3d^{10} \, 4p^6
To determine the correct electron configuration for the selenium ion ( \text{Se}^{2-} ), we start with the electron configuration of neutral selenium (( \text{Se} )), which has an atomic number of 34. The electron configuration for neutral selenium is:
[
\text{Se}: [\text{Ar}] \, 4s^2 \, 3d^{10} \, 4p^4
]
The notation ([\text{Ar}]) represents the electron configuration of the noble gas argon, which accounts for the first 18 electrons (1s² 2s² 2p⁶ 3s² 3p⁶).
Selenium typically gains two electrons to achieve a stable octet configuration, particularly in its common oxidation state of -2. Therefore, the electron configuration for ( \text{Se}^{2-} ) will include these additional two electrons. We add these electrons to the highest energy sublevel, which is the 4p sublevel:
Starting from the neutral configuration:
- Neutral selenium (( \text{Se} )): ([ \text{Ar}] \, 4s^2 \, 3d^{10} \, 4p^4)
- Adding two electrons to the 4p sublevel gives us ( 4p^6 ).
Thus, the electron configuration for ( \text{Se}^{2-} ) becomes:
[
\text{Se}^{2-}: [\text{Ar}] \, 4s^2 \, 3d^{10} \, 4p^6
]
Now, let’s analyze the options provided:
- A. ([Ar] \, 4s^2 \, 3d^{10} \, 4p^6) (Correct)
- B. ([Ar] \, 4s^2 \, 3d^{10} \, 4p^2) (Incorrect)
- C. ([Ar] \, 4s^2 \, 3d^{10} \, 4p^4) (Incorrect)
- D. ([Ar] \, 4s^2 \, 4d^{10} \, 4p^6) (Incorrect)
In conclusion, the correct electron configuration for ( \text{Se}^{2-} ) is option A: [Ar] \, 4s^2 \, 3d^{10} \, 4p^6. This configuration shows that selenium, in its anionic form, achieves a full outer shell of electrons, contributing to its stability.