* Electron Configuration: Chlorine has 7 electrons in its outermost shell. By gaining one electron, it achieves a stable octet configuration, fulfilling the octet rule. This makes Cl- a negatively charged ion.

* Repulsion: Adding another electron to Cl- would create a highly unstable species with two extra electrons in its outermost shell. This would result in significant repulsion between the negatively charged electrons, making it highly unfavorable.

* Electrostatic Forces: The negative charge on Cl- already repels other negatively charged particles. Attracting another electron would further intensify this repulsion.

In summary: Cl- is already stable with a full octet and a negative charge. It would require a significant amount of energy to overcome the electrostatic repulsion and force it to accept another electron.