* Chlorine's atomic number is 17, meaning it has 17 protons and 17 electrons in its neutral state.
* Chlorine gains one electron to become a chloride ion (Cl-), resulting in a total of 18 electrons.
* Argon's atomic number is 18, so it also has 18 electrons.
Therefore, the chloride ion (Cl-) has the same electron configuration as argon, with a full outer shell of 8 electrons.
Neon, on the other hand, has 10 electrons, so its electron configuration is different from chlorine and chloride ions.
