* Chlorine's Neutral State: A neutral chlorine atom has 17 electrons. Its electron configuration is 2, 8, 7. This means it has 7 electrons in its outermost shell (valence shell).
* Octet Rule: Atoms tend to gain or lose electrons to achieve a stable configuration with 8 electrons in their valence shell. This is known as the octet rule.
* Gaining an Electron: Chlorine can achieve a stable octet by gaining one electron. When it gains an electron, it now has 18 electrons and a 1- charge. This is because it has one more electron than protons, which have a positive charge.
* Formation of Chloride Ion: This negatively charged chlorine atom is now called a chloride ion (Cl-).
In summary: Chloride ions have a 1- charge because they have gained one electron to complete their outer shell and achieve a stable octet configuration.
