Question

which of the following is the correct electron configuration of the chloride ion (cl⁻)?
1s²2s²2p⁶3s²3p⁵
1s²2s²2p⁶3s²3p⁴
1s²2s²2p⁶3s²3p⁶
1s²2s²2p⁶

Explanation:

Step1: Recall chlorine's atomic number

Chlorine (Cl) has atomic number 17.

Step2: Determine electrons in chloride ion

Chloride ion (Cl⁻) has one extra electron, so 17 + 1=18 electrons.

Step3: Write electron - configuration

Filling orbitals according to Aufbau principle, we get 1s²2s²2p⁶3s²3p⁶.

Answer:

1s²2s²2p⁶3s²3p⁶