Final answer:
The octet rule is the principle stating that atoms form compounds in ways that give them eight electrons in their valence shell for stability, similar to the electron configuration of noble gases.
Step-by-step explanation:
The principle that states atoms tend to form compounds so that each atom can have eight electrons in its outermost energy level is known as the octet rule. According to the octet rule, atoms seek to have an electron configuration similar to that of the nearest noble gas, which is typically characterized by a valence shell containing eight electrons. This rule suggests that atoms are more stable energetically when they achieve a full valence shell, which often involves sharing, losing, or gaining electrons through bonding with other atoms. Exceptions to the octet rule do exist such as helium, which is stable with only two valence electrons, and hydrogen which also achieves stability with a pair of electrons in its valence shell.
However for most main group elements, attaining an octet contributes to chemical stability and dictates the formation of many ionic and covalent compounds. The octet rule is an essential concept in understanding chemical bonding and reactivity.