If an atom has fewer than 8 electrons in the outermost energy level, it is likely to form chemical bonds with other atoms in order to achieve a stable electron configuration of 8 electrons in the outermost energy level.
According to the octet rule, if an atom has fewer than 8 electrons in the outermost energy level, it is likely to either gain, lose, or share electrons in order to achieve a stable electron configuration with a full outermost energy level. This is because atoms tend to be more stable when they have a full valence shell, which typically consists of 8 electrons.
