IB Chemistry on Resonance, Delocalization and Formal Charges

1. FORMAL CHARGE (FC)
Tool/Model for comparing which Lewis structures is more acceptable
Lewis structure SO2
Which is acceptable?
Lewis structure SO3
Formal Charge
•Treats covalent bond with equal electron distribution no EN diff bet atom
•Electronegative atom has negative while least electronegative atom
has positive formal charge.
Formula formal charge
Click herevideo formal charges
Click herevideo formal charges
V -valence electronsof atom
L–Lone pair electron
B -electrons shared incovalent bonds in the molecule
✓
✓
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
L+
Formal charge concept

2. FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge carbon dioxide
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
L+
FC = 6 –(4+2) = 0
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
formal charge for C
V-Valence electron C = 4
L -Lone pair electron C = 0
B -Bonding electron C = 8
FC = 4 –(0+4) = 0
✓
Lowest formal charge is preferred
L+
L+
L+

3. Formal charge carbon dioxide
Formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
Formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
Formal charge for C
V-Valence electron C = 4
L -Lone pair electron C = 0
B -Bonding electron C = 8
FC = 4 –(0+4) = 0
✓
Lowest formal charge is preferred
Different Lewis structures for CO2
Which is acceptable?
0
0
0
0
-1
+1
-1
+2
-1
0
-2
+2
Lowest formal charge is preferred
✓
Click herevideo CO2
Lowest formal charge –more stable -contribute more to diff resonance structures.
Sum of formal charges must be zero for neutral or equal to charge on ion.
L+
L+
L+

4. Formal charge dinitrogen oxide
Formal charge for N
Formal charge for N
Formal charge for O
V-Valence electron N = 5
L-Lone pair electron N = 2
B-Bonding electron N = 6
V-Valence electron N = 5
L-Lone pair electron N = 0
B-Bonding electron N = 8
V-Valence electron O = 6
L-Lone pair electron O = 6
B-Bonding electron O = 2
FC = 5 –(2+3) = 0
FC = 5 –(0+4) = +1
FC = 6 –(6+1) = -1
+1
0
-1
Different Lewis structures for N2O
-2
+1
+1
+1
-1
0
0
+1
-1
-1
+2
-1
-2
+2
0
Lowest formal charge is preferred
✓
Click hereto view video
Which is acceptable?
Lowest formal charge is preferred
✓
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
L+
L+
L+

5. Delocalization of electrons
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
Resonance structures carbonate ion
2
3 CO
resonance structure 1 resonance structure 2 resonance structure 3
Resonance hybrid
• All bonds CO3
2- are identical in length and strength
• Hybrid of 3 resonance structures
• Negative charge equally distributed over all oxygen
• No O-O (single) or O=O (double) bonds found
• Only O -----O bond
• Intermediate in character bet single and double bond
• Bond Order = 3
1 1
Carbonate Ion
• charge 2- delocalized into 2/3-
• lower charge – more stable
Click here on video carbonate
C

6. All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge carbonate ion
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 6
B-Bonding electron O = 2
L+
FC = 6 –(6 +1) = -1
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
formal charge for C
V-Valence electron C = 4
L -Lone pair electron C = 0
B -Bonding electron C = 8
FC = 4 –(0+4) = 0
-1
-1
0
0
✓
L+
L+
L+

7. Delocalization of electrons
Resonance structures nitrate ion

3 NO
resonance structure 1 resonance structure 2 resonance structure 3
resonance hybrid
• All bonds NO3
- are identical in length and strength
• Hybrid of 3 resonance structures
• Negative charge equally distributed over all oxygen
• No N-O (single) or N=O (double) bonds found
• Only N -----O bond
• Intermediate in character bet single and double bond
• Bond Order = 3
1 1
Nitrate Ion
charge of -1 delocalized into 1/3-
lower charge – more stable
Click here to view video
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
1/3
1/3 1/3

8. All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge nitrate ion
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 6
B-Bonding electron O = 2
L+
FC = 6 –(6 +1) = -1
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
formal charge for N
V-Valence electron N = 5
L -Lone pair electron N = 0
B -Bonding electron N = 8
FC = 5 –(0+4) = +1
-1
-1
+1
0
✓
L+
L+
L+

9. Delocalization of electrons
Resonance structures nitrite ion

2 NO
resonance structure 1 resonance structure 2
resonance hybrid
• All bonds NO2
- are identical in length and strength
• Hybrid of 2 resonance structures
• Negative charge equally distributed over all oxygen
• NO N-O (single) or N=O (double) bonds found
• Only N ----- O bond
• Intermediate in character bet single and double bond
• Bond Order = 2
1 1
Nitrite Ion
charge of -1 delocalized into 1/2-
lower charge – more stable
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
Click here video nitrite

10. All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge nitrite ion
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
L+
FC = 6 –(4 +2) = 0
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 6
B-Bonding electron O = 2
FC = 6 –(6+1) = -1
formal charge for N
V-Valence electron N = 5
L -Lone pair electron N = 2
B -Bonding electron N = 6
FC = 5 –(2+3) = 0
-1
0
0
✓
L+
L+
L+

11. Delocalization of electrons
Resonance structures sulfur dioxide
2 SO
resonance structure 1 resonance structure 2
• All SO2 bonds are identical in length and strength
• Hybrid of 2 resonance structures
• Negative charge equally distributed over all oxygen
• NO S-O (single) or S=O (double) bonds found
• Only S -----O bond
• Intermediate in character bet single and double bond
• Bond Order = 2
1 1
Sulfur Dioxide
Click here to view
S
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
resonance structure 3
How about structure 3?
resonance hybrid

12. FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge sulfur dioxide
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
L+
FC = 6 –(4 +2) = 0
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
formal charge for S
V-Valence electron S = 6
L -Lone pair electron S = 2
B -Bonding electron S = 8
FC = 6 –(2+4) = 0
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge, contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
✓
0
0
0
✓
L+
L+
L+

13. Formal charge Sulfur dioxide
Formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4 +2) = 0
Formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
Formal charge for S
V-Valence electron S = 6
L -Lone pair electron S = 2
B -Bonding electron S = 8
FC = 6 –(2+4) = 0
✓
Lowest formal charge is preferred
Different Lewis structures for SO2
Which is acceptable?
Lowest formal charge is preferred
✓
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable) contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
0
0
0
0
0
0
0
+1
-1
0
+1
-1
Click hereto view
L+
L+
L+

14. Delocalization of electrons
Resonance structure cyanate
resonance structure 1 resonance structure 2
Cyanate ion
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
resonance structure 3
Which structure is
acceptable ?
-1 0 0 0 0 -1 +1 0 -2
Contribute the MOST
Negative formal charge located on more electronegative O atom is
more stable than one located on a less electronegative N atom
Lowest formal charge is preferred
✓
0 0 -1
✓
Contribute the least
High formal charge/unstable
✓
χ χ
Contribute less
Negative formal charge on
less electronegative N atom
- NCO
Click here to view

15. Delocalization of electrons
Xenon trioxide
Resonance
•Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
Which structure is
acceptable ?
3 XeO
Click here to view
Different resonance structure for XeO3
✓
Lowest formal charge is preferred
formal charge for O
V- Valence electron O = 6
L- Lone pair electron O = 4
B- Bonding electron O = 4
FC = 6 – (4 +2) = 0
formal charge for Xe formal charge for O
V- Valence electron Xe = 8
L- Lone pair electron Xe = 2
B- Bonding electron Xe = 12
V- Valence electron O = 6
L- Lone pair electron O = 4
B- Bonding electron O = 4
FC = 8 – (2 +6) = 0 FC = 6 – (4 +2) = 0
0 0
0
0
L + L + L +

16. Delocalization of electrons
Resonance structures sulfur trioxide
resonance structure 1 resonance structure 2
• All SO3 bonds are identical in length and strength
• Hybrid of 3 resonance structures
• NO S-O (single) or S=O (double) bonds found
• Only S -----O bond
• Intermediate in character bet single and double bond
• Bond Order = 3
1 1
Sulfur Trioxide 3 SO
resonance structure 3
S 120
Click here to view video
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
resonance structure 4
How about structure 4 ?
resonance hybrid

17. Formal charge Sulfur Trioxide
Formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4 +2) = 0
Formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
Formal charge for S
V-Valence electron S = 6
L -Lone pair electron S = 0
B -Bonding electron S = 12
FC = 6 –(0+6) = 0
✓
Lowest formal charge is preferred
Different Lewis structures for SO3
Which is acceptable?
Lowest formal charge is preferred
✓
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
0
0
0
0
0
0
0
0
0
-1
-1
+2
0
-1
-1
+2
0
+2
-1
-1
L+
L+
L+

18. Delocalization of electrons
Resonance structures methanoate
resonance structure 1 resonance structure 2
• All CO bonds are identical in length and strength
• Hybrid of 2 resonance structures
• NO C-O (single) or C=O (double) bonds found
• Only C ----- O bond
• Intermediate character bet single and double bond
• Bond Order = 2
1 1
Methanoate ion
 HCOO
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
Click here to view
resonance hybrid
Click here to view
Resonance structures ethanoate
Ethanoate ion
 CH COO 3
resonance structure 1 resonance structure 2
resonance hybrid
H H
CH3

19. FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge methanoate ion
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 6
B-Bonding electron O = 2
L+
FC = 6 –(6 +1) = -1
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
FC = 6 –(4+2) = 0
formal charge for C
V-Valence electron C = 4
L -Lone pair electron C = 0
B -Bonding electron C = 8
FC = 4 –(0+4) = 0
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
✓
0
0
-1
0
L+
L+
L+

20. Delocalization of electrons
Resonance structures thiocyanate
resonance structure 1 resonance structure 2
Thiocyanate ion
 SCN
Click here to view video
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
resonance structure 3
Which is acceptable
structure?
-1 0 0 0 0 -1 +1 0 -2
Contribute the MOST
Negative formal charge located on more electronegative N atom is
more stable than one located on a less electronegative S atom
Lowest formal charge is preferred
✓
0 0 -1
✓
Contribute the least
High formal charge/unstable
✓
χ χ
Contribute the less
Negative formal charge on
less electronegative S atom

21. Formal charge thiocyanate ion
Formal charge for S
Formal charge for C
Formal charge for N
V-Valence electron S = 6
L-Lone pair electron S = 4
B-Bonding electron S = 4
V-Valence electron C = 4
L-Lone pair electron C = 0
B-Bonding electron C = 8
V-Valence electron N = 5
L-Lone pair electron N = 4
B-Bonding electron N = 4
FC = 6 –(4+2) = 0
FC = 4 –(0+4) = 0
FC = 5 –(4+2) = -1
0
0
-1
Different Lewis structures for SCN-
0
-1
0
Lowest formal charge is preferred
✓
Which is acceptable?
Lowest formal charge is preferred
✓
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
0
0
-1
+1
0
-2
Click hereto view video
L+
L+
L+

22. Delocalization of electrons
Resonance structures ozone
resonance structure 1 resonance structure 2
resonance hybrid
• All bonds O-O are identical in length and strength
• Hybrid of 2 resonance structures
• NOO-O (single) or O=O (double) bonds found
• Only O -----O bond
• Intermediate in character bet single and double bond
• Bond Order = 2
1 1
Ozone
3 O
Click here on video ozone
Resonance
• Describing delocalization of electrons within a molecule/polyatomic ion
where bonding cannot be express by ONE single Lewis structure
•Delocalization of π bond – π electrons spread over more than 2 nuclei
•π electrons are shared
•π electrons spread – more stable
• Pale blue gas, polar, dimagnetic
• Oxidizing agent
• Potent respiratory hazard and pollutant at ground level
• Beneficial prevent UV B/C from reaching Earth surface
• Highest ozone level in stratosphere,(10 km and 50 km)
UV radiation
Ozone at stratosphere
strongest radiation
3 O

23. FORMAL CHARGE (FC)
Formal Charge
•Tool/Model for comparing which Lewis structures is more acceptable
•Treats covalent bond with equal electron distribution no electronegativity differences bet atom
•Electronegative atom has negative while least electronegative atom has positive formal charge
Formula formal charge
V -valence electronsof atom
L –lone pair electron
B –bonding electron molecule
✓
Formal charge sulfur dioxide
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 4
B-Bonding electron O = 4
L+
FC = 6 –(4 +2) = 0
formal charge for O
V-Valence electron O = 6
L-Lone pair electron O = 6
B-Bonding electron O = 2
FC = 6 –(6+1) = -1
formal charge for O
V-Valence electron O = 6
L -Lone pair electron O = 2
B -Bonding electron O = 6
FC = 6 –(2+3) = +1
All resonance structure contribute to electronic structure.
Real structure is combination of them.
Lowest formal charge (stable), contribute more than less stable structure.
Sum of formal charges must be zero for neutral or equal to charge on ion.
✓
0
+1
-1
✓
L+
L+
L+

24. Ozone Good and Bad
Good Side
Bad Side
Ozone in Strastophere
•blocks UV B + C
Ozone in Troposphere act as
•Greenhouse gas
Ozone in ground level act as
•Pollutant
•Photochemical
Click hereon ozone depletion
chemicals (phaseout)
Why ozone able to absorb UV B and UV C?
Breakdown of ozone –High UV radiation
–Skin cancer
-DNA mutation
Ozone depletion
UV Exposure