This document provides a tutorial on formal charges, resonance structures, and delocalization of electrons. It explains that formal charge is a tool used to determine which Lewis structure of a molecule or polyatomic ion is more accurate. The structure with the lowest overall formal charge is usually preferred. Resonance structures show delocalized bonding, with the actual structure being a combination or "resonance hybrid" of the contributing structures. Examples discussed include carbon dioxide, the carbonate ion, dinitrogen oxide, the nitrate ion, and the nitrite ion.

1. Tutorial on Resonance, Delocalization and
Formal Charges.
Prepared by
Lawrence Kok
http://lawrencekok.blogspot.com

2. FORMAL CHARGE (FC)
Tool/Model for comparing which Lewis structures is more acceptable
Lewis structure SO2
Which is
acceptable?
Lewis structure SO3
Formal charge
concept
✓ ✓

3. 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
L +
V - valence electrons of atom
L – Lone pair electron
B - electrons shared in covalent bonds in the molecule
Formal charge
concept

4. 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 here video formal charges Click here video formal charges
V - valence electrons of atom
L – Lone pair electron
B - electrons shared in covalent 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

5. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge carbon dioxide
formal charge for O
L +
formal charge for C formal charge for O
L + L + L +

6. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge carbon dioxide
formal charge for O
L + L + L +
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

7. Formal charge carbon dioxide
Formal charge for O
L + L + L +
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
Different Lewis structures for CO2
Which is
acceptable?

8. Formal charge carbon dioxide
Formal charge for O
L + L + L +
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 -1 0 +1 -1 +2 -1 0 +2 -2
✓
Lowest formal charge is preferred
Click here video 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.

9. Formal charge dinitrogen oxide
Formal charge for N Formal charge for N Formal charge for O
L + L + L +
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
0 +1 -1
Different Lewis structures for N2O
Which is acceptable?

10. Formal charge dinitrogen oxide
Formal charge for N Formal charge for N Formal charge for O
L + L + L +
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
0 +1 -1
Different Lewis structures for N2O
0 +1 -1 -2 +1 +1 0 +1 -1 -1 +2 -1 -2 +2 0
✓
Lowest formal charge is preferred
Click here to 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.

11. 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
Carbonate Ion
resonance structure 1 resonance structure 2 resonance structure 3
C

12. 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
1 1
• Bond Order = 3
Carbonate Ion
• charge 2- delocalized into 2/3-
• lower charge – more stable
Click here on video carbonate
C

13. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge carbonate ion
formal charge for O
L +
formal charge for C formal charge for O
L + L + L +

14. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge carbonate ion
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 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 +

15. 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 nitrate ion
-
3 NO
Nitrate Ion
resonance structure 1 resonance structure 2 resonance structure 3

16. 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 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 = 1 1
3
Nitrate Ion
charge of -1 delocalized into 1/3-
lower charge – more stable
Click here to view video
1/3
1/3 1/3

17. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge nitrate ion
formal charge for O
L +
formal charge for N formal charge for O
L + L + L +

18. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge nitrate ion
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 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 +

19. 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 nitrite ion
-2
NO
Nitrite Ion
resonance structure 1 resonance structure 2

20. 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 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
1 1
• Bond Order = 2
Nitrite Ion
charge of -1 delocalized into 1/2-
lower charge – more stable
Click here video nitrite

21. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge nitrite ion
formal charge for O
L +
formal charge for N formal charge for O
L + L + L +

22. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge nitrite ion
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 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
0 0 -1
✓
L + L + L +

23. 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 sulfur dioxide
2 SO
Sulfur Dioxide
resonance structure 1 resonance structure 2
S
resonance structure 3
How about
structure 3?
resonance hybrid

24. 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 sulfur dioxide
2 SO
resonance structure 1 resonance structure 2
• All SObonds are identical in length and strength
2 • 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
1 1
• Bond Order = 2
Sulfur Dioxide
Click here to view
S
resonance structure 3
How about
structure 3?
resonance hybrid

25. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge sulfur dioxide
formal charge for O
L +
formal charge for S formal charge for O
L + L + L +

26. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge sulfur dioxide
formal charge for O
L + L + L +
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.
0
0 0 Lowest formal charge, contribute more than less stable structure.
✓
Sum of formal charges must be zero for neutral or equal to charge on ion.✓

27. 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
0
Different Lewis structures for SO2
Which is acceptable?
0 0
0
+1
0 0 0
-1 0
Click here to view
+1
-1
L + L + L +

28. 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 ✓
0
0 0
Different Lewis structures for SO2
Which is acceptable?
Lowest formal charge is preferred
✓
+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
0 0 0
-1 0
Click here to view
+1
-1
L + L + L +

29. 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 structure cyanate
Cyanate ion
resonance structure 1 resonance structure 2
resonance structure 3
Which structure is
acceptable ?
NCO-

30. 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 structure cyanate
Cyanate ion
resonance structure 1 resonance structure 2
resonance structure 3
Which structure is
acceptable ?
χ χ
-1 0 0 0 0 -1 +1 0 -2
Lowest formal charge is preferred
Negative formal charge located on more electronegative O atom is
more stable than one located on a less electronegative N atom
Contribute the MOST
✓
0 0 -1
✓
Contribute the least
High formal charge/unstable
✓
Contribute less
Negative formal charge on
less electronegative N atom
NCO-Click
here to view

31. 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
Xenon trioxide
3 XeO Click here to view
Which structure is
acceptable ?
Different resonance structure for XeO3
formal charge for O formal charge for Xe formal charge for O
L + L + L +

32. 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
Xenon trioxide
3 XeO Click here to view
Which structure is
acceptable ?
Different resonance structure for XeO3
✓
Lowest formal charge is preferred
formal charge for O
L + L + L +
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

33. 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 sulfur trioxide
Sulfur Trioxide 3 SO
resonance structure 1 resonance structure 2
resonance structure 3
S 120
resonance structure 4
How about
structure 4 ?
resonance hybrid

34. 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 sulfur trioxide
resonance structure 1 resonance structure 2
• All SObonds are identical in length and strength
3 • 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
1 1
• Bond Order = 3
Sulfur Trioxide 3 SO
resonance structure 3
S 120
Click here to view video
resonance structure 4
How about
structure 4 ?
resonance hybrid

35. 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
Which is acceptable? 0
0 0
0
Different Lewis structures for SO3
0
L + L + L +

36. Formal charge Sulfur Trioxide
Formal charge for O
L + L + L +
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 ✓
0
0 0
0
Different Lewis structures for SO3
Which is acceptable?
0
✓
0
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
-1
-1
+2
0
-1
-1
+2
0
+2
-1 -1

37. 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 methanoate
resonance structure 1 resonance structure 2
Resonance structures ethanoate
• 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
1 1
• Bond Order = 2
Methanoate ion
HCOO-
resonance hybrid
Click here to view
Click here to view
Ethanoate ion
CH COO- 3
resonance structure 1 resonance structure 2
resonance hybrid
H H
CH3

38. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge methanoate ion
formal charge for O
L +
formal charge for C formal charge for O
L + L + L +

39. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge methanoate ion
formal charge for O
L + L + L +
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
All resonance structure contribute to electronic structure.
0
Real structure is combination of them.
0 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

40. 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 thiocyanate
Thiocyanate ion
SCN-
resonance structure 1 resonance structure 2
resonance structure 3
Which is acceptable
structure?
-1 0 0 0 0 -1 +1 0 -2

41. Delocalization of electrons
Resonance structures thiocyanate
Thiocyanate ion
SCN-
resonance structure 1 resonance structure 2
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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?
χ χ
-1 0 0 0 0 -1 +1 0 -2
Lowest formal charge is preferred
Negative formal charge located on more electronegative N atom is
more stable than one located on a less electronegative S atom
Contribute the MOST
✓
0 0 -1
✓
Contribute the least
High formal charge/unstable
✓
Contribute the less
Negative formal charge on
less electronegative S atom

42. Formal charge thiocyanate ion
Formal charge for S Formal charge for C Formal charge for N
L + L + L +
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 0 -1
Which is acceptable?
-1 0 0 +1 0 -2

43. 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-
Lowest formal charge is preferred ✓
0 0 -1
✓
Which is acceptable?
Lowest formal charge is preferred
-1 0 0 +1 0 -2
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.
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L + L + L +

44. 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 ozone
resonance structure 1 resonance structure 2
resonance hybrid
• All bonds O-O are identical in length and strength
• Hybrid of 2 resonance structures
• NO O-O (single) or O=O (double) bonds found
• Only O ----- O bond
• Intermediate in character bet single and double bond
1 1
• Bond Order = 2
Ozone 3 O
Click here on video ozone
UV radiation
• 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)
Ozone at stratosphere
strongest radiation
3 O

45. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge ozone
formal charge for O
L +
formal charge for O formal charge for O
L + L + L +

46. 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 electrons of atom
L – lone pair electron
B – bonding electron molecule ✓
Formal charge ozone
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.
+1
Lowest formal charge (stable), contribute more than less stable structure.
0 -1
Sum of formal charges must be zero for neutral or equal to charge on ion. ✓
✓
L + L + L +

47. 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 here on 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

48. Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenses
http://spaceplace.nasa.gov/greenhouse/en/
http://www.ozonedepletion.info/education/part3/ozonesources.html
http://creativecommons.org/licenses/
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorial
http://lawrencekok.blogspot.com