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Useful Concepts |
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Resonance Structures: How to get them !
The best way to "derive" resonance structures is by learning to "push"
curly
arrows and starting from a reasonable
Lewis
structure.
Rules to remember for recognising resonance structures:
-
Atoms never move.
-
You can only move electrons in p bonds or lone
pairs (that are in p orbitals)
-
The overall charge of the system must remain the same.
Ranking resonance structures (for 1st row atoms, in order of importance):
-
Octet rule should be satisfied.
-
Charge separation requires energy (think electrostatics)
-
Charge separation against that predicted by electronegativity.
Here is an example. Note how the possible resonance structures are derived
from the starting point by pushing curly arrows.
