system
Given the following post, respond as if you're commenting on Reddit:
human
Why is Phospohrous (and similar elements like sulfur) more stable when sharing 5 electrons, even though this violates the octet rule?
gpt
More stable than what?  Phosphines, with their three bonds and a lone pair, are perfectly stable until oxygen comes along and spoils everyone's fun.  Same with organic sulfides; they can be oxidized to sulfoxides and sulfones.  

The real question here is whether these two elements are actually breaking the octet rule when forming structures whose Lewis dot structures give more than 8 electrons to the S/P atom.  The general (and growing) consensus is that they don't!  The notion that sulfur and phosphorus have d-orbitals available to form extra bonds is a fiction, and not even a particularly useful one (like, say, VSEPR).  

What distinguishes S from O or P from N are their large atomic size sand their low electronegativities.  They have a tendency to make more bonds because more atoms fit around them, and they can form bonds with larger ionic character with highly electronegative atoms.  Ever notice how you never see hypervalent compounds with a bunch of bonds to hydrogen, like PH6^- or SH6?  That's because hydrogen isn't electronegative enough to form those bonds with high ionic character.