* Chlorine's Electron Configuration: Chlorine has 17 electrons. Its electron configuration is 2-8-7, meaning it has 7 electrons in its outermost shell (the third shell).

* The Octet Rule: Atoms tend to be most stable when they have 8 electrons in their outermost shell (with the exception of hydrogen and helium, which only need 2). This is known as the octet rule.

* Chlorine's Need for Stability: Since chlorine has 7 electrons in its outer shell, it needs one more electron to achieve a stable octet.

How Chlorine Achieves Stability:

To become stable, chlorine can:

* Gain an electron: This forms a chloride ion (Cl-), which has a negative charge. This is a common way chlorine achieves stability in ionic compounds.

* Share an electron: Chlorine can form covalent bonds with other atoms by sharing electrons. This is how chlorine forms molecules like chlorine gas (Cl2).

In short: Chlorine needs to gain one electron to become stable. It can achieve this by forming ionic bonds or covalent bonds.