* Octet Rule: Atoms strive to have a full outer shell of electrons, which usually contains 8 electrons (the "octet rule"). This configuration provides stability.

* Iodine's Electron Configuration: Iodine has 7 electrons in its outermost shell.

* Gaining an Electron: By gaining one electron, iodine completes its outer shell, reaching a stable configuration with 8 electrons. This makes it an anion with a -1 charge (I⁻).

Important Note: Non-metals generally gain electrons to become stable, forming negatively charged ions (anions). This is in contrast to metals, which tend to lose electrons to become positively charged ions (cations).