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