The electronic configuration of chlorine is 2, 8, 7, indicating that it has two electrons in the first energy level, eight in the second, and seven in the third (outer) energy level. Chlorine’s valency is determined by the number of electrons needed to achieve a stable, noble gas configuration. As chlorine requires one more electron to complete its outer shell, its valency is 1. This valency corresponds to the number of electrons chlorine can gain or share to achieve the stable configuration of the noble gas argon, which has eight electrons in its outermost energy level.