Question

what is the electron configuration for this particle?
cl⁻
1s² 2s² 2p⁶ 3s² 3p⁵
1s² 2s² 2p⁶ 3s² 3p⁴
1s² 2s² 2p⁶ 3s² 3p⁶
1s² 2s² 2p⁶

Explanation:

1. First, find the atomic number of neutral chlorine (Cl): it is 17, so a neutral Cl atom has 17 electrons, with the electron configuration $1s^2 2s^2 2p^6 3s^2 3p^5$.
2. The ion $\text{Cl}^-$ has a -1 charge, meaning it has gained 1 extra electron, giving it a total of 18 electrons.
3. Add this extra electron to the 3p subshell (the highest energy subshell in neutral Cl), filling it completely.

Answer:

1s² 2s² 2p⁶ 3s² 3p⁶