Final answer:
The octet rule is the principle stating that atoms tend to gain, lose, or share electrons to end up with eight valence electrons, resembling the electron configuration of noble gases and achieving maximum stability.
Step-by-step explanation:
The rule that states atoms attempt to acquire an outermost energy level with eight electrons is known as the octet rule. This rule reflects the observation that atoms, apart from noble gases, tend to share, lose, or gain valence electrons to achieve a valence shell resembling that of a noble gas, which typically contains eight electrons. Underlying this tendency is the principle that atoms become more stable when they possess eight electrons in their valence shell, the consequence of which is the formation of more stable compounds. The octet rule is especially applicable to the main group elements where acquiring an octet corresponds to an electron configuration ending in s²p6.
Atoms with fewer than eight electrons in their valence shell will often react to reach this stable state. For example, oxygen, which has six electrons in its outer shell, can form covalent bonds with hydrogen atoms to complete its octet, resulting in water molecules (H2O). Thus, according to the octet rule, atoms aim for a complete octet to attain maximum stability, releasing energy in the process and becoming energetically more stable.