* Electron Configuration: Chlorine has 17 electrons, with the following configuration: 2, 8, 7. This means it has 7 electrons in its outermost shell, which is called the valence shell.
* Octet Rule: Atoms tend to gain, lose, or share electrons to achieve a full outer shell of 8 electrons (known as the octet rule). This configuration is considered stable and unreactive.
* Gaining an Electron: Chlorine is one electron away from having a full outer shell. Therefore, it is more energetically favorable for chlorine to *gain* one electron to become a negatively charged ion (anion) with a -1 charge.
The process:
1. A neutral chlorine atom (Cl) gains an electron to become a chloride ion (Cl-).
2. This makes its outermost shell complete with 8 electrons, fulfilling the octet rule.
3. The extra negative charge from the gained electron results in the -1 charge.
In summary: Chlorine forms a -1 ion because gaining one electron allows it to achieve a stable electron configuration with a full outer shell, following the octet rule.
