Oxidation Numbers

Oxidation Numbers• An oxidation number is the charge (or the

apparent charge) of an element in a formula.

H2O

Fe

+1 -2

0

SO42-

+6 -2

NaCl+1 -1

Oxidation Numbers

1) The sum of the oxidation numbers for each atom in a formula is ALWAYS equal to the total charge of the formula!

NaCl

Fe

+1 -1

0

SO42-

+6 -2

H2O+1 -2

Oxidation Numbers

2) The oxidation number for free elements is ALWAYS zero (0)!

3) The oxidation number for monoatomic ions is ALWAYS equal to the charge of the ion!

Na Cl2 S

Na1+ Cl1- S2-

0 0 0

+1 -1 -2

Oxidation Numbers4) When they are bonded to different elements…

a) The oxidation number for group 1 elements is ALWAYS +1! (except hydrogen)

b) The oxidation number for group 2 elements is ALWAYS +2!

c) The oxidation number for silver (Ag) is ALWAYS +1!

d) The oxidation number for zinc (Zn ) is ALWAYS +2!

e) The oxidation number for aluminum (Al) is ALWAYS +3!

f) The oxidation number for fluorine (F) is ALWAYS -1!

Na

Zn

Al

F

Ca

Ag

Oxidation Numbers

“The Sweet Sixteen Elements”

Oxidation Numbers

5) The oxidation number for hydrogen is USUALLY +1.

In hydrides, the oxidation number for hydrogen is –1.

6) The oxidation number for oxygen is USUALLY –2.

In peroxides, the oxidation number for oxygen is –1.

In OF2, the oxidation number for oxygen is +2.

H

O

Oxidation Numbers

7) The more electronegative element is assigned the negative oxidation number

8) In BINARY formulas, the oxidation number for:

a) group 17 elements is USUALLY –1.

b) group 16 elements is USUALLY –2.

c) group 15 elements is USUALLY –3.

Cl

S

N

Oxidation Numbers

9) In ALL formulas for compounds and ions, metals ALWAYS have a positive oxidation number.

10) In MOST formulas, the first part is assigned a positive oxidation number and the second part is assigned a negative oxidation number.

NO2 NH3KBr-2+4 +1 -1 +1-3

Oxidation Numbers

Ex. (1) CaCl2

Ex. (2) XeF2

Ex. (3) Hg22+

Ex. (4) S8

+2 -1

-1+2

+1

0

Oxidation Numbers

Ex. (5) F1-

Ex. (6) KHCO3

Ex. (7) Pb

Ex. (8) FeSO4

-1

+1 +1 -2+4

0

-2

-2

+6+2

Oxidation Numbers

Ex. (9) SO3

Ex.(10) MnO42-

Ex.(11) Cu1+

Ex.(12) NH4NO3

-2+6

-2+6

+1

+1 -2

-1+1

+5-3

Oxidation Numbers

Ex.(13) Sn(NO3)2

Ex.(14) CaH2

Ex.(15) C2O42-

Ex.(16) I2

-2

-1

+5+2

+2 -1

-2+3

0

Oxidation Numbers

Ex.(17) SO32-

Ex.(18) N2O5

Ex.(19) NiS

Ex.(20) PCl5

-2+4

-2+5

-2+2+

-1+5

Oxidation Numbers

Ex.(21) Na2O2

Ex.(22) AlCl3

Ex.(23) NH3

Ex.(24) NaClO

+1 -1

+3 -1

+1-3

+1 -2+1

Oxidation Numbers

Ex.(25) Ag

Ex.(26) Zn3(PO4)2

Ex.(27) S2O32-

Ex.(28) O22-

0

+2 -2+5

-3

-2+2

-1

Oxidation Numbers

Ex.(29) KNO3

Ex.(30) Ag2CrO4

Ex.(31) Na2X

Ex.(32) M2O

+1 -2+5

+1 -2+6

+1 -2

-2+1