What happens when chlorine atom gains an electron in its outer energy shell?

Explanation:

Atomic number of chlorine is 17 and its electronic configuration is as follows.

Since, to become stable in nature chlorine requires only one electron from a donor atom.

As it is known that species that gain electrons will obtain a negative charge and species that lose electrons will obtain a positive charge.

Hence, when chlorine will gain an electron to become stabilized then it will change into chlorine ion or ion.