List the rules for assigning oxidation numbers:
1.
2.
3.
4.
5.
the oxidation number of any free, uncombined elements is zero
the oxidation number of any monatomic ion is the charge of the ion
fluorine is always -1
hydrogen is nearly always +1, except when bonded to a metal element then hydrogen is -1
oxygen is nearly always -2 except: when bonded to fluorine oxygen is +2; when oxygen is used
as a peroxide ion (O2 bonded to a group 1 or group 2 element) then oxygen is -1
6. the sum of all the oxidation numbers in a neutral compound is zero
7. the sum of all the oxidation numbers in a polyatomic ion is the charge of the ion
8. when non-metals only are bonded together in a compound or an ion the less electronegative
element (+charge) is written first (exceptions where more electronegative element (-charge) is
written first: NH3, NH4+1, OH-1)
assign oxidation numbers to each element in the following compounds or polyatomic ions:
+1 -1
1. K2S
+3 +3 -2
6. Al2(C2O4)3
+1 +5 -2
11. Cs3PO4
+6 -2
16. SO3
+2 -1
2. CaBr2
+1 +3 -1
7. Ra(NO2)2
0
12. Ag
+4 -2
17. SO3-2
+1 +6 -2
3. K2CrO4
+2 +5 -2
8. Ga(ClO3)2
+2 -1
13. HgBr2
+2 -1
18. CaH2
+2 +3 -2
4. Sr3(PO4)2
0
9. O2
+1 -2
14. ClO-1
-3 +1
19. NH4+1
+2 +5 -2
5. Mg(NO3)2
+3 -2
10. Al2O3
+5 -2
15. PO4-3
0
20. H2
NOTE: change to formula (C2O4)3