Here's why:
* Chlorine has 7 valence electrons (electrons in its outermost shell).
* To achieve a stable octet (8 electrons) like the noble gases, chlorine needs to gain one electron.
* Gaining an electron gives chlorine a negative charge, resulting in the formation of a chloride ion (Cl⁻).
Other elements that can form ions with a negative one charge include:
* Fluorine (F)
* Bromine (Br)
* Iodine (I)
* These elements are all halogens and have similar electron configurations.
