1. Identify the preceding noble gas: Chlorine (Cl) is in the third row of the periodic table, so the preceding noble gas is Argon (Ar).
2. Write the noble gas symbol in brackets: [Ar]
3. Continue the electron configuration from there: Chlorine has 17 electrons, and Argon has 18. So, we need to add the remaining 7 electrons. Chlorine is in the p-block, so we fill the 3p orbitals:
[Ar] 4s² 3d¹⁰ 4p⁵
Therefore, the noble gas shorthand electron configuration for chlorine is [Ar] 4s² 3d¹⁰ 4p⁵.
