Resonance Structures:  alternate but equiv. Lewis dot structures

NO₃^-

Exceptions to Octet Rule in Lewis Struct:

· odd # e-

· atom w/ less than octet

· atom w/ more than octet

Electronegativity: ability for atom in molec. to attract e- to itself

Formal Charge: charge that an atom in molec. would have if all atoms had same electroneg

(NOT REAL CHARGE)

Assign:

1. all unshared e- to atom on which they are found

2. half of bonding e- to ea atom

Form Charge: # val e^- - # e^-  assigned 

= overall charge of molecule or ion

most stable Lewis Struct when:

§ atom w/  ↓  formal charge

§ neg charges on more electroneg element