Exceptions to the Octet Rule
C, N, O, F always follow the octet rule.
Be and B usually have fewer that 8 electrons.
Third period and lower elements can exceed the octet rule.
Try to satisfy the octet rule then, place any extra electrons on an element in the third period
or lower.
!! !
P
Cl
ClCl
Cl Cl
Resonance Structures
Draw the Lewis structure for NO3-
Resonance occurs when more than one equivalent Lewis structure can be drawn.
Resonance is needed because the localized electron model can not accurately display the true
arrangement of the electrons.
The true structure is a combination of all the resonance forms. It is not one of the structures
but all of them superimposed.
1
Ex: PCl5 P- 5e-
Cl- 7e- x5= 35e-
Total- 40e-
Use 10 e- to form bonds, leaving 30 e-
