FORMAL CHARGE (FC) Tool/Model for comparing which Lewis structures is more acceptable Lewis structure SO 2 Which is acceptable? Lewis structure SO 3 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
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IB Chemistry on Resonance, Delocalization and Formal Charges
IB Chemistry on Resonance, Delocalization and Formal Charges
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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 chargesClick 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.
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
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 – (4+2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
formal charge for C
V- Valence electron C = 4L - Lone pair electron C = 0B - Bonding electron C = 8
FC = 4 – (0+4) = 0
✓ Lowest formal charge is preferred
L + L + L +
Formal charge carbon dioxide
Formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
Formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
Formal charge for C
V- Valence electron C = 4L - Lone pair electron C = 0B - Bonding electron C = 8
FC = 4 – (0+4) = 0
✓Lowest formal charge is preferredDifferent 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 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.
V- Valence electron N = 5L- Lone pair electron N = 2B- Bonding electron N = 6
V- Valence electron N = 5L- Lone pair electron N = 0B- Bonding electron N = 8
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 5 – (2+3) = 0 FC = 5 – (0+4) = +1 FC = 6 – (6+1) = -1
+10 -1
Different Lewis structures for N2O
-2 +1 +1+1 -10 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.
Resonance • Describing delocalization of electrons within a molecule/polyatomic ionwhere bonding cannot be express by ONE single Lewis structure•Delocalization of π bond – π electrons spread over more than 2 nuclei
• All bonds CO32- 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
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 electrons of atom
L – lone pair electron
B – bonding electron molecule✓
Formal charge carbonate ion
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
L +
FC = 6 – (6 +1) = -1
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
formal charge for C
V- Valence electron C = 4L - Lone pair electron C = 0B - Bonding electron C = 8
• 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 = 311
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
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 electrons of atom
L – lone pair electron
B – bonding electron molecule✓
Formal charge nitrate ion
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
L +
FC = 6 – (6 +1) = -1
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
formal charge for N
V- Valence electron N = 5L - Lone pair electron N = 0B - Bonding electron N = 8
FC = 5 – (0+4) = +1
-1-1+1
0
✓
L + L + L +
Delocalization of electrons
Resonance structures nitrite ion
2NO
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 = 211
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
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 electrons of atom
L – lone pair electron
B – bonding electron molecule✓
Formal charge nitrite ion
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 – (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 – (6+1) = -1
formal charge for N
V- Valence electron N = 5L - Lone pair electron N = 2B - Bonding electron N = 6
FC = 5 – (2+3) = 0
-10 0✓
L + L + L +
Delocalization of electrons
Resonance structures sulfur dioxide
2SO
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 = 211
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
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
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 – (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
formal charge for S
V- Valence electron S = 6L - Lone pair electron S = 2B - 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
00 ✓
L + L + L +
Formal charge Sulfur dioxide
Formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4 +2) = 0
Formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
Formal charge for S
V- Valence electron S = 6L - Lone pair electron S = 2B - Bonding electron S = 8
FC = 6 – (2+4) = 0
✓Lowest formal charge is preferredDifferent 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.
Resonance • Describing delocalization of electrons within a molecule/polyatomic ionwhere 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 ismore stable than one located on a less electronegative N atom
Resonance •Describing delocalization of electrons within a molecule/polyatomic ionwhere 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 ?
3XeOClick here to view
Different resonance structure for XeO3
✓
Lowest formal charge is preferred
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4 +2) = 0
formal charge for Xe formal charge for O
V- Valence electron Xe = 8L- Lone pair electron Xe = 2B- Bonding electron Xe = 12
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
• 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 = 311
Sulfur Trioxide 3SO
resonance structure 3
S 120
Click here to view video
Resonance • Describing delocalization of electrons within a molecule/polyatomic ionwhere bonding cannot be express by ONE single Lewis structure•Delocalization of π bond – π electrons spread over more than 2 nuclei
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4 +2) = 0
Formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
Formal charge for S
V- Valence electron S = 6L - Lone pair electron S = 0B - 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
00
0
0 0
0
0
0
-1
-1
+2
0
-1
-1
+2
0
+2
-1-1
L +L + L +
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 = 211
Methanoate ionHCOO
Resonance • Describing delocalization of electrons within a molecule/polyatomic ionwhere bonding cannot be express by ONE single Lewis structure•Delocalization of π bond – π electrons spread over more than 2 nuclei
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
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
L +
FC = 6 – (6 +1) = -1
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
FC = 6 – (4+2) = 0
formal charge for C
V- Valence electron C = 4L - Lone pair electron C = 0B - 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 +
Delocalization of electrons
Resonance structures thiocyanate
resonance structure 1 resonance structure 2
Thiocyanate ionSCN
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 acceptablestructure?
-1 0 0 0 0 -1 +1 0 -2
Contribute the MOST
Negative formal charge located on more electronegative N atom ismore stable than one located on a less electronegative S atom
V- Valence electron S = 6L- Lone pair electron S = 4B- Bonding electron S = 4
V- Valence electron C = 4L- Lone pair electron C = 0B- Bonding electron C = 8
V- Valence electron N = 5L- Lone pair electron N = 4B- Bonding electron N = 4
FC = 6 – (4+2) = 0 FC = 4 – (0+4) = 0 FC = 5 – (4+2) = -1
00 -1
Different Lewis structures for SCN-
0 -10
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.
• 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
• Bond Order = 211
Ozone3O
Click here on video ozone
Resonance • Describing delocalization of electrons within a molecule/polyatomic ionwhere 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)
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
V- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4
L +
FC = 6 – (4 +2) = 0
formal charge for O
V- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2
FC = 6 – (6+1) = -1
formal charge for O
V- Valence electron O = 6L - Lone pair electron O = 2B - 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 +
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