An ion is an atom in which the total number of electrons is
not the same with the total number of protons, giving it a net positive or
negative electrical charge.
The electron configuration of chlorine is [Ne]3s23p5. If a
chlorine atom adds an electron to form the chloride ion (Cl-), it will have an
electron configuration of [Ne]3s23p6. While Argon has no charge.
