OXIDATION NUMBERS
... is a special name given to the charges of the elements of a compound. This information helps us decide where electrons should be found inside a compound.
... in the case of ionic compounds ­ most of the time the oxidation numbers are exactly the same as the common charges for each element BUT NOT ALWAYS!!
.... in covalent compounds ­ the most electronegative element will usually take on a negative oxidation number (since this element has a strong pull on electrons near it). ... Hydrogen has two possible oxidation numbers: ­1 for hydrides
+1 for acids ... Oxygen has three possible oxidation numbers:
­1 if part of a peroxide (O2­2 ion)
­2 if in an oxides (O­2 ion)
+2 if oxygen is bonded to fluorine. .... All other atoms can be determined to acquire the appropriate overall charge for the molecule. If there are two possible answers, both must be provided!!
1
Examples:
Cl2
Cu+2
H2O
OF2
N2
Cl­1
Cu2S
CO2
O2
Al+3
LiH
NO
O2­2
NO2
K2O2
CuO2
NO3
NO2
S8
Cu
KNO3
Be3(PO4)2
Al(OH)3
NaS
­1
Cr2O7
­2
H3OF
Al(NO3)3
AlH3
Al(NO2)3
H2SO4
H2CO3
2
3
4
5