Name:_____________________________
Worksheet โ ASSIGNING OXIDATION NUMBERS
Oxidation Number Rules:
1. The oxidation number of any pure element is 0.
2. The oxidation number of a monatomic ion equals that charge on the ion.
3. The more electronegative element in a binary compound is assigned the number equal to the
charge it would have if it were an ion.
4. The oxidation number of fluorine in a compound is always -1.
5. Oxygen has an oxidation number of -2 unless it is combined with F, in which it is +1 or +2, or it
is in peroxide (such as H2O2 or Na2O2), in which it is -1.
6. Hydrogen is +1, unless combined with a metal, and then it is -1.
7. In compounds, Group 1 is +1, Group 2 is +2, and Aluminum is +3.
8. The sum of the oxidation numbers of all atoms in a neutral compound is 0.
9. The sum of the oxidation numbers in a polyatomic ion equals the charge of the ion.
Part A: In the following questions, give the oxidation number of the indicated atoms/ion:
1. N in N2O3 __________
2. S in H2SO4 __________
3. C __________
4. C in CO __________
5. Na in NaCl __________
6. H in H2O __________
7. Ba in BaCl2 __________
8. N in NO2- __________
9. S in Al2S3 __________
10. S in HSO4- __________
11. Cl in Fe(ClO2)3 __________
12. Fe in Fe(ClO2)3 __________
13. N in NO3- __________
14. Cu2+ __________
15. Zn2+ __________
16. C in CH4 __________
17. Mn in MnO2 __________
18. S in SO32- __________
19. Mg2+ __________
20. Cl- __________
21. O2 __________
22. P4 __________
23. Na in Na2S __________
24. S in H2S __________
25. Ca2+ __________
26. C in CN- __________
27. H in OH- __________
28. Mn in KMnO4 __________
29. I in Mg(IO3)2 __________
30. C in C2O42- __________
+3
+6
0
+2
+1
+1
+2
+3
-2
+6
+3
+3
+5
+2
+2
-4
+4
+4
+2
-1
0
0
+1
-2
+2
-4
+1
+7
+5
+3
