ib chemistry on resonance, delocalization and formal charges

http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Tutorial on Resonance, Delocalization andFormal Charges.

FORMAL CHARGE (FC)

Tool/Model for comparing which Lewis structures is more acceptable

Lewis structure SO2 Which is acceptabl

e?

Lewis structure SO3

✓ ✓

Formal charge concept

FORMAL CHARGE (FC)

Tool/Model for comparing which Lewis structures is more acceptable

Lewis structure SO2 Which is acceptabl

e?

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

V - valence electrons of atom L – Lone pair electronB - electrons shared in covalent bonds in the molecule

✓ ✓

L +

Formal charge concept

FORMAL CHARGE (FC)

Tool/Model for comparing which Lewis structures is more acceptable

Lewis structure SO2 Which is acceptabl

e?

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 electronB - 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

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 electronB – bonding electron molecule

✓Formal charge carbon dioxide

formal charge for O

L +

formal charge for Oformal charge for C

L + L + L +

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 electronB – 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

Different Lewis structures for CO2

Which is acceptable?

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.

L +L + L +

Formal charge dinitrogen oxide

Formal charge for N Formal charge for N Formal charge for O

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

Which is acceptable?

L + L + L +

Formal charge dinitrogen oxide

Formal charge for N Formal charge for N Formal charge for O

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.

L + L + L +

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

23CO

resonance structure 1 resonance structure 2 resonance structure 3

Carbonate Ion

C

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

23CO

resonance structure 1 resonance structure 2 resonance structure 3

Resonance hybrid

• 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

• Bond Order = 311

Carbonate Ion

• charge 2- delocalized into 2/3-• lower charge – more stable

Click here on video carbonate

C

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 electronB – bonding electron molecule

✓Formal charge carbonate ion

formal charge for O

L +

formal charge for Oformal charge for C

L + L + L +

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 electronB – 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

FC = 4 – (0+4) = 0

-1

-1

0

0✓

L + L + L +

Delocalization of electrons

Resonance structures nitrate ion

3NO

resonance structure 1 resonance structure 2 resonance structure 3

Nitrate 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

Delocalization of electrons

Resonance structures nitrate ion

3NO

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

11

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

1/31/3

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 electronB – bonding electron molecule

✓Formal charge nitrate ion

formal charge for O

L +

formal charge for Oformal charge for N

L + L + L +

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 electronB – 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

Nitrite 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

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•π electrons are shared•π electrons spread – more stable

Click here video nitrite

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 electronB – bonding electron molecule

✓Formal charge nitrite ion

formal charge for O

L +

formal charge for Oformal charge for N

L + L + L +

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 electronB – 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

Sulfur Dioxide

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

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•π electrons are shared•π electrons spread – more stable

resonance structure 3

How about structure 3?

resonance hybrid

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 electronB – bonding electron molecule

✓Formal charge sulfur dioxide

formal charge for O

L +

formal charge for Oformal charge for S

L + L + L +

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 electronB – 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.

✓00

0 ✓

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

Different Lewis structures for SO2

Which is acceptable?

0 00

000 0

+1-1 0

+1

-1

Click here to view

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.

0 00

000 0

+1-1 0

+1

-1

Click here to view

L +L + L +

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 ?

-NCO

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

✓

-100✓

Contribute the least

High formal charge/unstable

✓

χχ

Contribute less

Negative formal charge on less electronegative N atom

-NCO

Click here to view

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 ?

3XeOClick here to view

Different resonance structure for XeO3

formal charge for O formal charge for Xe formal charge for O

L + L + L +

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 ?

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

FC = 8 – (2 +6) = 0 FC = 6 – (4 +2) = 0

0 0

0

0

L + L + L +

Delocalization of electrons

Resonance structures sulfur trioxide

resonance structure 1 resonance structure 2

Sulfur Trioxide 3SO

resonance structure 3

S 120

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

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 = 311

Sulfur Trioxide 3SO

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

Formal charge Sulfur Trioxide

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 = 0B - Bonding electron S = 12

FC = 6 – (0+6) = 0

Different Lewis structures for SO3

Which is acceptable? 0

00

0

0

L +L + L +

Formal charge Sulfur Trioxide

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 = 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 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 ionCOOCH3

resonance structure 1 resonance structure 2

resonance hybrid

HH

CH3

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 electronB – bonding electron molecule

✓Formal charge methanoate ion

formal charge for O

L +

formal charge for Oformal charge for C

L + L + L +

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 electronB – 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

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

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 is more stable than one located on a less electronegative S atom

Lowest formal charge is preferred

✓

-100✓

Contribute the least

High formal charge/unstable

✓

χχ

Contribute the less

Negative formal charge on less electronegative S atom

Formal charge thiocyanate ion

Formal charge for S Formal charge for C Formal charge for N

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

Which is acceptable?

0 0-1 +1 0 -2

L + L +L +

Formal charge thiocyanate ion

Formal charge for S Formal charge for C Formal charge for N

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.

0 0-1 +1 0 -2

Click here to view video

L + L +L +

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• 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 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

3O

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 electronB – bonding electron molecule

✓Formal charge ozone

formal charge for O

L +

formal charge for Oformal charge for O

L + L + L +

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 electronB – bonding electron molecule

✓Formal charge ozone

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

Ozone depletion

UV Exposure

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://spaceplace.nasa.gov/greenhouse/en/http://www.ozonedepletion.info/education/part3/ozonesources.htmlhttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com