**In general, the most stable structures are those in which each atom forms as many bonds as
unfilled electron states are available in their valence shells.
**Double bonds tend to be shorter than single bonds between the same atoms because of a
stronger net attraction between bonding electrons and their atomic nuclei.
Resonance: valence electrons are delocalized across more than one covalent bond.
Electrons get delocalized → KE goes down, PE goes down
**Net decrease in total energy stabilizes the molecule
Free radicals: have unpaired valence electrons and can be neutra