Question

what is the electron configuration for this particle? cl⁻
1s²2s²2p⁶3s²3p⁶
1s²2s²2p⁶
1s²2s²2p⁶3s²3p⁵
1s²2s²2p⁶3s²3p⁴

Explanation:

1. First, find the atomic number of neutral chlorine (Cl): it is 17, so a neutral Cl atom has 17 electrons.
2. The Cl⁻ ion has gained 1 electron to achieve a full outer shell, so it has 17 + 1 = 18 electrons total.
3. Fill orbitals in order of increasing energy: 1s holds 2, 2s holds 2, 2p holds 6, 3s holds 2, 3p holds 6. Summing these (2+2+6+2+6=18) matches the total electrons in Cl⁻.

Answer:

1s² 2s² 2p⁶ 3s² 3p⁶