Resonance Structures

[salvadorramos3k]

Will there ever be a time where a molecule has an element that does not have a complete octet? Also, if you draw a resonance structure with an incomplete octet, is it still valid but just very unstable? What should a "correct" resonance structure look like?

[Haley Fredricks 1B]

There are very few exceptions to the octet rule (in terms of it not being completed). Boron and Aluminum are the two that most often don't complete an octet (having 6 valence electrons instead of 8)

[Matthew Tsai 2H]

The common exceptions of atoms that do not require at least a full octet are the first four elements, along with boron and aluminum. Otherwise, there aren't really any naturally occurring examples of an element that doesn't fill its octet so any resonance structures that break the rule wouldn't be valid.

[Amy Kumar 1I]

For boron, not having an octet and having just 6 shared electrons makes it formal charge 0 since it has 6 valence electrons. This is favorable for boron rather than having a complete octet.