Final answer:
The octet rule states that atoms are most stable when they have eight electrons in their outermost shells. However, there are exceptions to this rule for certain elements.
Step-by-step explanation:
The octet rule states that atoms are most stable when they have eight electrons in their outermost shells. This means that the outermost shell of an element can hold a maximum of eight electrons. However, it is important to note that the octet rule applies to main group elements and exceptions exist for some elements. For example, hydrogen only needs two electrons to fill its valence shell and does not follow the octet rule.