14.3 Delocalization of Electrons (HL)
*When the unhybridized ____orbitals on ________ or more atoms are arranged so that they form a continuous
overlapping sequence, the shared pi electrons can spread over more than two atoms. A _______________
bond is one in which the electrons spend all their time shared between just _______ atoms. The electrons in a
____________________ bond become ____________ among more than _______ atoms.
*Hint: If there are two or more equivalent Lewis structures (i.e. ______________ structures) that can be
drawn for a molecule, then what actually occurs is a mid-way between these various possibilities.
Examples:
1) Benzene
a)The sigma bond framework
b)Unhybridized p-orbitals
c) Pi bonding delocalization
2) Carbonate
Summary
Structurepi
forbonds
Carbonate Ion
Delocalized
Resonance in the Carbonate Ion
..
:O
.. _
:O:
C
:O
.. :_
CO32_ ..
:O
..
..
O:
C
:O
.. :_
_ ..
:O
..
_2
.. _
:O :
C
O
.. :
_
.. _ 2/3
O:
2/3
..
:O
C
:
O
.. _
2/3
THREE EQUIVALENT STRUCTURES
RESONANCE HYBRID
3) Ozone
Delocalized pi bonds
Practice:
a) Draw resonance structures and then the delocalized pi bonds for the following: nitrate (NO3-), nitrite (NO2-)
and the methanoate ion (HCOO-).
14.3 Practice: Resonance and Delocalization
Resonance Structure 1
Resonance Structure 2
Resonance Structure 3
Delocalized Structure
nitrate ion
carbonate ion
Resonance Structure 1
Resonance Structure 2
Delocalized Structure
nitrite ion
ozone
benzene
carboxylate ion
More practice  Draw all resonance structures for: SO2, SO3, SCN-