SCH 4U1
Oxidation Numbers
Oxidation numbers are imaginary numbers that are used to describe
the locations of electrons.
Rules for assigning oxidation numbers
1) All elements are zero (they pull on the electron with equal strength)
2) Assign the most electronegative element by group
3) Assign the least electronegative metal by group
4) Assign the last element mathematically (*see bottom for example)
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
m)
n)
o)
p)
Cl2
HCl
NaF
KOH
OH1NH3
Li2SO4
HgClO2
NO31NO
F 2O
NH41+
KMnO4
K2MnO4
MnO2
K2Cr2O7
* CaCO3
1) Assign oxygen as 2- (it is closest to fluorine on the P. T. and in group VI)
2) Assign calcium as 2+ (furthest from fluorine on the P. T. and in group II)
3) let carbon be x in the example CaCO3 [2 + x + 3(-2) = 0]
x = -2 + 6
x=4
Caution – the answer doesn’t always equal the group!