ib chemistry on redox, oxidation states, oxidation number

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http://lawrencekok.blogspot.com Prepared by Lawrence Kok Video Tutorial on Redox, Oxidation, Reduction and oxidation number.

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http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Video Tutorial on Redox, Oxidation, Reduction and oxidation number.

Cations/Metals/+ve ions

Gp 1 Gp 2 Gp 3 Transition metals ions ( variable oxidation states)

Oxidation state

+1

Oxidation state+2

Oxidation state

+3

Sc+3

Ti+2+3

V+2+3

Cr+2+3+6

Mn+2+3+6+7

Fe+2+3

Co+2+3

Ni+2

Cu+1+2

Zn+2

Li 1+ Be2+ Sc 3+ Ti 2+

Ti 3+

V 2+

V 3+

Cr 2+

C r3+

Cr6+

Mn 2+

Mn 3+

Mn 6+

Mn 7+

Fe 2+

Fe 3+

Co2+

Co 3+

Ni2+ Cu1+

Cu2+

Zn2+

Na 1+ Mg2+ Al 3+

K 1+ Ca2+

Anion/Non metal

Gp 5 Gp 6 Gp 7

Oxidation state

Oxidation state

Oxidation state

-3 -2 -1

N3- O2- F-1

P3- S2- CI-1

Br-1

I-1

Metal/Cations/+ve ions

Non Metal/Anions/-ve ions

Ionic Compound

Li2O MgCI2 Al2O3 FeOIron(II) oxide

NiONickel(II) oxide

CuOCopper(II) oxide

Li3N Mg3N2 AlN Fe3N2

Iron(II) nitrideNi3N2

Nickel(II) nitrideCu3N2

Copper(II) nitride

Oxidation state/Charge ion → Li1+ O2-

Formula compound Li2 O

1

Video on polyatomic ions

Writing Chemical Formula

Step 1 : Write Oxidation state/charge

Step 2 : Balance it, (electrically neutral) by cross multiply – as subscript

Polyatomic ions

Group of non-metals bonded together

Oxidation state

Oxidation state

Oxidation state

-1/+1 -2 -3

(OH)-1

Hydroxide(SO4)2-

Sulphate(PO4)

3-

Phosphate

(CN)-1

Cyanide(SO3)

2-

Sulphite

(SCN)-1

Thiocyanate(CO3)

2-

Carbonate

(NO3)-1

Nitrate(S2O3)

2-

Thiosulphate

(NO2)-1

Nitrite(Cr2O7)

2-

Dichromate

(NH4)+1

Ammonium

Polyatomic ions

Li2(CO3) Mg(CO3) Al2(CO3)3 Fe(CO3) Ni(CO3) Cu(CO3)

Li(OH) Mg(OH)2 Al(OH)3 Fe(OH)2 Ni(OH)2 Cu(OH)2

Li2(SO4) Mg(SO4) Al2(SO4)3 FeSO4 Ni(SO4) Cu(SO4) Video on polyatomic ions

Ionic Compound

Writing Chemical Formula

Metal/Cations/+ve ions

Cations/Metals/+ve ions

Gp1 Gp 2 Gp3 Transition metals ions ( variable oxidation states)

Oxidation state

+1

Oxidation state+2

Oxidation state

+3

Sc+3

Ti+2+3

V+2+3

Cr+2+3+6

Mn+2+3+6+7

Fe+2+3

Co+2+3

Ni+2

Cu+1+2

Li 1+ Be2+ Sc 3+ Ti 2+

Ti 3+

V 2+

V 3+

Cr 2+

C r3+

Cr6+

Mn 2+

Mn 3+

Mn 6+

Mn 7+

Fe 2+

Fe 3+

Co2+

Co3+

Ni2+ Cu1+

Cu2+

Na 1+ Mg2+ Al 3+

K 1+ Ca2+

Oxidation state/Charge ion → Li1+ (CO3)2-

Formula compound Li2 (CO

3)1

Step 1 : Write Oxidation state/charge ion

Step 2 : Balance it, (electrically neutral) by cross multiply – as subscript

Redox (Oxidation and Reduction)

Oxidation – Gain of oxygen ↑

Oxidation – Loss of hydrogen ↓ Reduction – Gain of hydrogen ↑

Reduction – Loss of oxygen ↓

Oxidation Reduction

Gain oxygen ↑ Loss oxygen ↓

Gain oxidation Number ↑

Loss oxidation Number ↓

Loss hydrogen ↓ Gain hydrogen ↑

Loss electron ↓ Gain electron ↑

Ca + O2 CaO→ CH4 + 2O2 CO→ 2+ 2H2Ogain oxygen gain oxygen

Zn + CuO ZnO + Cu→ PbO + CO Pb + CO→ 2loss oxygen loss oxygen

H2S + CI2 S +2HCI →loss hydrogen

H2S + CI2 S + 2HCI →

Redox - Oxidation state change- Electron transfer

CH4 + 2O2 → CO2 + 2H2O

gain hydrogen

Zn + CuSO4 → ZnSO4 + Cu Zn + CI2 → ZnCI2

No gain/loss oxygen/hydrogen

Redox

gain oxygen

gain hydrogen

Reduction

Oxidation

Are these redox rxns?

Redox - Oxidation state change- Electron transfer

Zn + CuSO4 → ZnSO4 + Cu Zn + CI2 → ZnCI2 No gain/loss oxygen/hydrogen

Are these redox rxns?

Yes – change in oxidation numberYes – loss/gain of electron

Yes – change in oxidation numberYes – loss/gain of electron✓ ✓

• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity• + means lose electron• - means gain electron

Oxidation State/Number/ON Rules

Oxidation Reduction

Gain oxygen ↑ Loss oxygen ↓

Gain oxidation Number ↑

Loss oxidation Number ↓

Loss hydrogen ↓ Gain hydrogen ↑

Loss electron ↓ Gain electron ↑

H CIxx

xx

•x

∂-∂+

+1 -1Oxidation number

Oxidation state (sign, number) +2 NOT 2+

Oxidation state and formal charge useful tool for electron book- keeping. They are not REAL!- Oxidation state -Assume bond ionic with diff EN values (unless bet same element)- Formal charge – Assume bond covalent

Redox (Oxidation and Reduction)

Redox (Oxidation and Reduction)

• Assuming bond are ionic with diffEN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity• + means lose electron• - means gain electron

Oxidation Number/ON Rules

H CIxx

xx

•x

∂-∂+

+1 -1Oxidation number

Oxidation state (sign, number) +2 NOT 2+

Oxidation state and formal charge useful tool for electron book- keeping. They are not REAL!- Oxidation state -Assume bond ionic with diff EN values (unless bet same element)- Formal charge – Assume bond covalent

xx

CI CI

Oxidation Number/ON Rules

H CI Na CI

Imagine electron move to more EN element

O C O

oo

oo

xxoo

oo xx

xxox

Equal sharing

xx

xx

xx

ox

+1 -1Unequal sharing

0 0

xx xx

xx

ox

+1 -1Complete transfer

oxox

oo

oo

oo

oo

oo

oo

xoxo

Unequal sharing

-2 +4 -2

H O H

CI2 H CI Na CI C O2

+1 -1 -1+1 +4 -2

oo

ox

ox

+1 -2 +1Unequal sharing

H N HH

ox

ox

o x

oo

+1 -3 +1

+1

Unequal sharing

H2 O N H3

H C H

H

H

o xo x

ox

ox

+1

+1

+1

+1 -4

C H4

+1 -2 -3 +1 -4 +1

CI C CI

CI

CI

-1

-1

-1

-1

xx

xx

xx

xx

xx xx

xx

xx

xx

xx

xx

xx

xo

xo

ox

ox

+4

C CI4

+4 -1

0

Exceptions

Element ON Exception Example

Hydrogen +1 H +1

-1 Bond to metalMetal hydride

NaHCaH2

Oxidation Number/States/ON Rules Imagine electron move to more EN element

• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

H CI

xx

∂-xx

•x

Oxidation number +1 -1

∂+

xx

H CIxx

xx

xx

+1 -1

ox

Unequal sharing

H CI+1 -1

Na Hox

+1 -1Complete transfer

Na H+1 -1

Exceptions

Element ON Exception Example

Oxygen -2 O -2

+2Bond to fluorine

F2O

Exceptions

Element ON Exception Example

Oxygen -2 O -2

-1Peroxide

(O-O)H2O2

H O H F O Foo

oo

ox

ox

+1 -2 +1Unequal sharing

H2 O+1 -2

oo

oo

xx

xx

xx

xx

xx

xxo x

o x

-1 +2 -1Unequal sharing

F2 O-1 +2

O O HH

O-O single bond

oo

oo

oo

oo

o x

o xoo

equal sharing

+1 -1 -1 +1Unequal sharing

H2 O2

+1 -1

EN fluorine higher ↑EN oxygen higher ↑

Oxidation Number/ON Rules Imagine electron move to more EN element

O O H O HOxidation state O different – depend element bond with – different EN values !

F O F O Oxx

xx

xx

xx

xxxx

Equal sharing

0 0

O20

oo

oo

oo

oo

o x

o x+1 -2 +1

Unequal sharing

H2 O+1 -2

xx xx

xx xx

xxxx

o x

o x

-1 +2 -1

F2 O-1 +2

H Hoo

oo

oo

oo

oo

o x

o x

+1 -1 -1 +1

H2 O2+1 -1

Unequal sharing Unequal sharing

Oxidation Number/ON Rules Imagine electron move to more EN element

• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

H CI

xx

∂-xx

•x

Oxidation number +1 -1

∂+

xx

Oxidation Number/ON Rules Imagine electron move to more EN element

O O H O HOxidation state O different – depend element bond with – different EN values !

F O F O Oxx

xx

xx

xx

xxxx

Equal sharing

0 0

O2

0

oo

oo

oo

oo

o x

o x

+1 -2 +1

Unequal sharing

H2 O+1 -2

xx xx

xx xx

xxxx

o x

o x

-1 +2 -1

F2 O-1 +2

H Hoo

oo

oo

oo

oo

o x

o x

+1 -1 -1 +1

H2 O2+1 -1

Unequal sharing Unequal sharing

Oxidation Number/ON Rules Imagine electron move to more EN element

Oxidation state N different – depend element bond with – different EN values !

H N HH

HH O N O H O N O N O N

O

O O

O

o x

o x

o x

x xx x

+1 -3 +1

+1

-2

[N H4 ]-3 +1 +1

Unequal sharing

xx

o x

o x xoxo

xx

oo

oo oo

oo

+1 -2 +3 -2

Unequal sharing

H N O2

+1 +3 -2

O

o x

o x xoxo

xx

oooo

oo

+1 -2 +5 -2

-2

Unequal sharing

H N O3

+1 +5 -2

o x

o x

xxoo

xxoo

oo

oo

oo

oo

oo

oo

oo

oo

oo oo -2

-2 -2

-5 -5-2

N2 O5

Unequal sharing

-5 +2

+1+

Oxidation Number/ON Rules

Atoms uncombined free element state = ON = 0

Ion form – ON same as charged on ion

1

2

Mg

Mg2+

Na

Na+

O2 S8

O2-

3 ON for element same as its most common ion/groupON metal from Gp 1 – 3ON non metal Gp 5 - 7

Anion/Non metal

Gp 5 Gp 6 Gp 7

Oxidation state

Oxidation state

Oxidation state

- 3 - 2 - 1

N 3- O 2- F 1-

P 3- S 2- CI 1-

Cation/Metal

Gp 1 Gp 2 Gp 3

Oxidation state

Oxidation state

Oxidation state

+1 +2 +3

Na 1+ Mg 2+ Al 3+

K 1+ Ca 2+ Ga 3+

4

CI20 0 0 0 0

+1 +2 -2 -1 -2

CI- S2-

ON for transition metal varies Transition metal ions

Transition metals ions (variable oxidation states)

Sc+3

Ti+2+3

V+2+3

Cr+2+3+6

Mn+2+3+6+7

Fe+2+3

Co+2+3

Ni+2

Cu+1+2

Zn+2

Sc 3+ Ti 2+

Ti 3+

V 2+

V 3+

Cr 2+

Cr 3+

Cr 6+

Mn 2+

Mn 3+

Mn 6+

Mn 7+

Fe 2+

Fe 3+

Co 2+

Co 3+

Ni 2+ Cu 1+

Cu 2+

Zn 2+

Oxidation number

Diff ONCharge on ion

Click here on oxidation rulesClick here view simple step

Notes

Sc3+

Charge on Sc

Oxidation number

+3

Oxidation state

-+3+

ON all atoms in polyatomic ion add up to charge of polyatomic ion

ON all atoms in neutral molecule add up to 0

CO3 2- SO4

2-

H2SO4 CO25

Oxidation Number/ON Rules

HNO3

(+1)2 + (+6) + (-2)4 = 0

+1 +6 -2

(+4) + (-2)2 = 0 (+1) + (+5) + (-2)3 = 0

+4 -2 +1 +5 -2

(+4) + (-2)3 = -2

+4 -2

(+6) + (-2)4 = -2

NO31-

+6 -2

(+5) + (-2)3 = -1

+5 -2

7 ON atom/molecule of element = 0 (NOT combined)

H2 CI2 O2 Fe Cu Mg0 0 0 0 0 0

8 Monoatomic ion – ON same as charged on ion

Ionic compound

Charge ion Oxidation number

MgF2 Mg 2+ F 1- Mg (+2) F (-1)

NaCI Na 1+ CI 1- Na (+1) CI (-1)

KBr K 1+ Br 1- K (+1) Br (-1)

CaI2 Ca 2+ I 1- Ca (+2) I (-1)

Li3N Li 1+ N 3- Li (+1) N (-3)

Al2O3 Al 3+ O 2- AI (+3) O (-2)

9Formula compound

Charge Oxidation number

Name using oxidation number

FeO Fe 2+ or 2+ +2 Iron (II) oxide

Fe2O3 Fe 3+ or 3+ +3 Iron (III) oxide

Cu2O Cu 1+ or 1+ +1 Copper (I) oxide

CuO Cu 2+ or 2+ +2 Copper (II) oxide

MnO2 Mn 4+ or 4+ +4 Manganese (IV) oxide

MnO4- Mn 7+ or 7+ +7 Manganese (VII) oxide

K2Cr2O7 Cr 6+ or 6+ +6 Potassium dichromate (VI)

Cr2O3 Cr 3+ or 3+ +3 Chromium (III) oxide

Click here view chemguide notes

6

Oxidation Number/ON Rules

9 Metal more than one oxidation states, Roman numeral used

Manganese ChromiumIonic

compoundMnSO4 MnO2 K2MnO4 KMnO4 K2Cr2O7 Cr2O3

OxidationNumber

(+2) + (+6) + (-2)4 = 0 Mn (+2)

(+4) + (-2)2 = 0Mn (+4)

(+1)2 + (+6) + (-2)4 = 0Mn (+6)

(+1) + (+7) + (-2)4 = 0Mn (+7)

(+1)2 + (+6)2 + (-2)7 = 0Cr (VI)

(+3)2 + (-2)3 = 0Cr (III)

IUPAC name

Manganese(II)

sulphate

Manganese (IV)

oxide

Manganese(VI)

Manganese(VII)

Chromium(VI)

Chromium(III)

Iron CopperIonic

compoundFeCI2 FeCI3 CuCI CuCI2

OxidationNumber

(+2) + (-1)2 = 0 Fe (+2)

(+3) + (-1)3 = 0 Fe (+3)

(+1) + (-1) = 0 Cu (+1)

(+2) + (-1)2 = 0 Cu (+2)

IUPAC name

Iron (II) chloride Iron (III) chloride Copper (I) chloride Copper (II) chloride

Vanadium

VO2 + VO 2+

(+5) + (-2)2 = +1 V (+5)

(+4) + (-2) = +2 V (+4)

Vanadium (V) Vanadium (IV)

ON for underlined element in ionic compound10

Na2SO3 Na2SO4 NaNO2 NaNO3 (SO3)2- (SO4)2-

(+1)2 + (+4) + (-2)3 = 0 (+1)2 + (+6) + (-2)4 = 0 (+1)+ (+3) + (-2)2 = 0 (+1)+ (+5) + (-2)3 = 0 (+4) + (-2)3 = -2 (+6) + (-2)4 = -2

ON for S = +4 ON for S = +6 ON for N = +3 ON for N = +5 ON for S = +4 ON for S = +6

+1 +4 -2 +1 +6 -2 +1 +3 -2 +1 +5 -2 +4 -2 +6 -2

Oxidation Number/ON Rules

11 ON for underlined element in compound

OH-1 PO4

3- S2O32- CN-1 OCI-1 H2O2 (HCO3)-1

(-2) + (+1) = -1 (+5) + (-2)4 = -3 (+2)2 + (-2)3 = -2 (+4) + (-5) = -1 (-2) + (+1) = -1 (+1)2 + (-1)2 = 0

ON for O = -2 ON for P = +5 ON for S = +2 ON for C = +4 ON for O = -2 ON for O = -1 ON for C = +4

(+1) + (+4) + (-2)3 = -1

-2 +1 +5 -2 +2 -2 +4 -5 -2 +1 +1 -1 +1 +4 -2

Oxidation Reduction

Gain oxygen ↑ Loss oxygen ↓

Loss hydrogen ↓ Gain hydrogen ↑

Redox (Oxidation and Reduction)

Rxn involve gain/loss of oxygen/hydrogen

CH4 + 2O2 → CO2 + 2H2O Gain hydrogen

Oxygen reduction

gain oxygen

Carbon oxidation

Rxn involve gain/loss of electron

Oxidation Reduction

Gain ON ↑ Loss ON ↓

Loss electron ↓ Gain electron ↑- broader definition- cover more rxn types

PbO + CO Pb + CO→ 2

Lead Reduction

gain oxygen

Carbon oxidation

(-4) (+4)

(0) (-2)

ON ↑

ON ↓oxygen reduced

carbon oxidized

PbO + CO Pb + CO→ 2

(+2) (0)lead reduced

(+2) (+4)

CH4 + 2O2 → CO2 + 2H2O

ON ↑carbon oxidized

ON ↓loss oxygen

Redox (Oxidation and Reduction)

• Assuming bond are ionic with diff EN values (unless bet same element)• Assign each atom, measure of electron control relative to atom in pure element• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

Oxidation Number/ON Rules

H CIxx

xx

•x

∂-∂+

+1 -1Oxidation numberOxidation state (sign, number) +2 NOT 2+

Oxidation state useful tool for electron book- keeping. They are not REAL!- Oxidation state -Assume bond ionic with diff EN values (unless bet same element)

xx

Na CI

Oxidation Number/ON Rules Imagine electron move to more EN element

xx

xx

xx

ox

+1 -1Complete transfer

Na CI+1 -1

Ionic compound

H CI

Covalent compound

xx

xx

+1 -1xx

ox

H CI

Unequal sharing+1 -1

Organic Covalent compound

H C O H

H

Hox

ox

o X

o X

ox

oo

-2+1

+1

+1

+1 -2

C H4 O

Unequal sharing

Still covalent bond

Treat as imaginary ionic (loss/gain of electron control)

Bonds are still covalent NOT ionic, keep track where electron going

-2 +1 -2

(+1) + (-1) = 0 (+1) + (-1) = 0

(-2) + (+1)4 + (-2) = 0

O S O

O

ooxx

ooxx

ooxx

-2 +6 -2

-2

S O3

+6 -2

(+6) + (-2)3 = 0Click here note ON for organic carbon

oo oo

oo

oo

oo

oo

ON for carbon is NOT -2

Oxidation Number/ON Rules• Assuming bond are ionic with diff EN values (unless bet same element)• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

- Oxidation state useful tool for electron book- keeping. They are not REAL!Oxidation state (sign, number) +2 NOT 2+

Click here here note ON carbon

H C C H

Oxidation state Carbon compound

-4 CH4

-3 C2H6

-2 CH3CI

-1 C2H2

0 CH2CI2

+1 CHCI2-CHCI2

+2 CHCI3

+3 C2CI6

+4 CCI4

ON carbon (Organic molecules)

Average oxidation number bet carbon is taken!

Different ON states

Don’t need to take average ON bet carbons

Oxidation state

Carbon compound

-3 and -1 CH3CH2OH

-3 and +1 CH3CHO

Different ON states

ox

ox

+1 -1 -1 +1

C2 H2

-1 +1

oxoxox

Equal sharing

(-1)2 + (+1)2 = 0

H C C O HH

H

o X

ox

o X o X oo

ox

ox

H

H

o X oo

ox

+1

+1

-2

+1

+1

+1

+1-1-3

C2 H6 O1

x +1 -2

2x + 6 -2 = 0 x = -2

ON C in CH3 = -3ON C in CH2 = -1Average ON C = -2

H C C OH

ox

+1

H

H

o Xo X

ox

o X oo

xoxo

oo

+1

+1 +1

-3 -2+1

C2 H4 O1

x +1 -2

2x + 4 -2 = 0 x = -1

ON for carbon is NOT -1

ON C in CH3 = -3ON C in CH = +1Average ON C = -1

ON C in CH3 = -3ON C in COOH = +1Average ON C = 0

+3

Oxidation Number/ON Rules• Assuming bond are ionic with different EN values (unless bet same element)• Apparent/imaginary charge it has when bonded to diff elements• Unequal sharing electron based on electronegativity

- Oxidation state useful tool for electron book- keeping. They are not REAL!Oxidation state (sign, number) +2 NOT 2+

Click here here note ON carbonON carbon (Organic molecules)

Average oxidation number bet carbon is taken!

Oxidation state carbon

Carbon compound

-3 and +3 CH3COOH

H C C O HH

H

o X

ox

o X o X oo

ox

ox

H

H

o X oo

ox

+1

+1

-2

+1

+1

+1

+1-1

C2 H6 O1

x +1 -2

2x + 6 -2 = 0 x = -2

ON C in CH3 = -3ON C in CH2 = -1Average ON C = -2

H C C OH

ox

+1

H

H

o Xo X

ox

o X oo

xoxo

oo

+1

+1 +1

-3 -2+1

C2 H4 O1

x +1 -2

2x + 4 -2 = 0 x = -1

ON for carbon is NOT -2

ON for carbon is NOT -1

ON C in CH3 = -3ON C in CH = +1Average ON C = -1

H C C O H

H O

H

+1

ox

o X

+1

+1

o X-3 -3

ox

+1

oo

oo

oo

ooxx

oo

ox

ox

-2

ON for carbon is NOT 0

C2 H4 O2

x +1 -2

2x + 4 -4 = 0 x = 0

Oxidation state carbon

Carbon compound

-3 and -1 CH3CH2OH

Oxidation state carbon

Carbon compound

-3 and +1 CH3CHO

NOT Redox rxn•NO Loss/gain electron•NO change in oxidation number

Concept Map

Type of chemical reaction

Combustion/Respiration rxn Displacement rxn

Synthesis rxn Decomposition rxn

Single Displacement

Double Displacement

Acid/Base rxn

Involve oxygen!!

CH4 + 2O2 CO→ 2+ 2H2O C6H12O6 +6O2 6CO→ 2+6H2O

Redox rxn•Loss/gain electron•Change in oxidation number

Zn + 2HCI H→ 2+ ZnCI2 Zn + CuO ZnO + Cu→

Redox rxn•Loss/gain electron•Change in oxidation number

KI + Pb(NO3)2 PbI→ 2 + KNO3

Type of chemical reaction

HCI + NaOH NaCI + H→ 2O MgO + 2HCI MgCI→ 2 + H2O 2H2 + O2 2H→ 2O 2KCIO3 2KCI + 3O→ 2

Redox rxn•Loss/gain electron•Change in oxidation number

Redox rxn•Loss/gain electron•Change in oxidation number

NOT Redox rxn•NO Loss/gain electron•NO change in oxidation number

H CI + Na O H NaCI + H→ 2 O+1 -1 +1 -2 +1 +1 -1 +1 -2

2H2 + O2 2H→ 2O0 0 +1 -2

2K CI O3 2K CI + 3O→ 2

+1 +5 -2 +1 -1 0

C6 H12 O6 + 6O2 6C O→ 2 + 6H2 O Zn + 2H CI H→ 2 + Zn CI2

0 +1 -1 0 +2 -1

K I + Pb (N O3)2 Pb I→ 2 + K N O3

+1 -1 +2 +5 -2 +2 -1 +1 +5 -2 0 +1 -2 0 +4 -2 +1 -2

Oxidation state

Carbon compound

-4 CH4

-3 C2H6

-2 CH3CI

-1 C2H2

0 CH2CI2

+1 CHCI2-CHCI2

+2 CHCI3

+3 C2CI6

+4 CCI4

Different ON/ states for Carbon Different ON/ states for sulphur

Carbon attach to H – ON lower ↓- Carbon less oxidized- Carbon attract electron

Carbon attach to CI/O (EN ↑) – ON higher ↑- Carbon more oxidized- Carbon lose electron

Oxidation state

Sulphur compound

-2 H4S

0 S8

+2 SCI3

+4 SO2

+4 SO3 2-

+6 SO3

+6 H2SO4

Sulphur attach to H /CI– ON lower ↓- Sulphur less oxidized- Sulphur attract electron

Sulphur attach to O (EN ↑) – ON higher ↑- Sulphur more oxidized- Sulphur lose electron

Oxidation numbers and name

Formula ion

Charge Oxidation number

Name using ON

CrO42- 2- ON for Cr +6 Chromate (VI)

Cr2O7 2- 2- ON for Cr +6 Dichromate (VI)

MnO4- 1- ON for Mn +7 Manganate (VII)

MnO42- 2- ON for Mn +6 Manganate (VI)

CIO - 1- ON for CI +1 Chlorate (I)

CIO3 - 1- ON for CI +5 Chlorate (V)

CIO2 - 1- ON for CI +3 Chlorate (III)

CIO4 - 1- ON for CI +7 Chlorate (VII)

Formula compound

Charge Oxidation number

Name using oxidation number

FeO Fe 2+ or 2+ +2 Iron (II) oxide

Fe2O3 Fe 3+ or 3+ +3 Iron (III) oxide

Cu2O Cu 1+ or 1+ +1 Copper (I) oxide

CuO Cu 2+ or 2+ +2 Copper (II) oxide

MnO2 Mn 4+ or 4+ +4 Manganese (IV) oxide

MnO4- Mn 7+ or 7+ +7 Manganese (VII) oxide

K2Cr2O7 Cr 6+ or 6+ +6 Potassium dichromate (VI)

Cr2O3 Cr 3+ or 3+ +3 Chromium (III) oxide

Period 2

Shared electron cloud closer to O

Electronegativity

Electronegativity (EN)•Tendency of atom to attract/pull shared/bonding electron to itself•EN value higher – pull/attract electron higher (EN value from 0.7 – 4)

EN highest EN lowest

Factors affecting EN value•Size of atom/distance – small size/distance – stronger attraction for electron•Nuclear charge – higher nuclear charge – stronger attraction for electron

Electronegativity•EN increase up a Group•EN increase across a Period

F

CI

Br

I

Size increase

Attraction electron decrease

EN lower

Size

Be+4

Li+3 B

+5 N+7

O+8 F

+9

EN increase across period 2

Nuclear charge

EN increase across period 2 Nuclear charge increase Strong attraction for electron

EN increase

Gp 17

C+6

EN decrease down gp 17

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 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 NOT real !!

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

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