1. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.

2. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Alkali Metals = +1

3. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Alkaline Earth Metals = +2

4. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Group 13 Boron Group = +3

5. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Group 15 Nonmetals = -3

6. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Group 16 Nonmetals = -2

7. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Halogens = -1

8. Assigning Oxidation Numbers
For ionic compounds, oxidation numbers can be assigned
using the expected charges from the periodic table.
Transition Metals depend on anion

9. Ionic Compounds
Example: +2 -1
MgCl2

10. Ionic Compounds
Example: +1 -2
Na2O

11. Ionic Compounds Fe2O3 ?? -2 Example:
We don’t know iron’s oxidation number from the periodic table since it is a transition metal. ?? -2
Fe2O3

12. Ionic Compounds Fe2O3 +3 -2 Example:
But since we know the compound is neutral, the oxidation numbers must add up to zero. Therefore, Fe has a +3 oxidation number in this compound.
Example: +3 -2
Fe2O3

13. Ionic Compounds Cr2O72- ?? -2 Example:
We don’t know chromium’s oxidation number from the periodic table since it is a transition metal. ?? -2
Cr2O72-

14. Ionic Compounds Cr2O72- +6 -2 Example:
But since this ion has a charge of -2, the oxidation numbers must add up to negative two. Therefore the oxidation number of Cr is +6
Example: +6 -2
Cr2O72-

15. Covalent Compounds
Covalent compounds are made of two nonmetals, which from the periodic table are always expected to be negative

16. Covalent Compounds
But since covalent compounds are neutral species, it is not possible for every element to retain its negative oxidation number

17. Covalent Compounds
ONLY THE MORE ELECTRONEGATIVE ELEMENT keeps its negative oxidation number. Other nonmetals must adapt to keep the compound neutral

18. Electronegativity Trend
Increases

19. SO2 Covalent Compounds -2
Example: -2
SO2
Since oxygen is the more electronegative element, it will have its normal oxidation number.

20. SO2 Covalent Compounds +4 -2
Example: +4 -2
SO2
The compound is neutral, so the oxidation number of sulfur will be sufficient to balance out the two oxygen atoms.

21. OF2 Covalent Compounds -1
Example: -1
OF2
Since fluorine is the more electronegative element, it will have its normal oxidation number.

22. OF2 Covalent Compounds +2 -1
Example: +2 -1
OF2
The compound is neutral, so the oxidation number of oxygen will be sufficient to balance out the two fluorine atoms.

23. PO43- Covalent Compounds -2
Example: -2
PO43-
Since oxygen is the more electronegative element, it will have its normal oxidation number.

24. PO43- Covalent Compounds +5 -2
Example: +5 -2
PO43-
The ion has a charge of negative three, so the oxidation numbers must add up to the total charge of the ion.

25. Ionic Compounds with Polyatomics
Example: +2
CaSO4
This is an ionic compound, so the charge of the metal cation is its oxidation number

26. Ionic Compounds with Polyatomics
Example: +2
CaSO4
The anion is a polyatomic ion, sulfate, and the charge of sulfate is negative two. So the oxidation numbers of sulfur and oxygen must add to -2

27. Ionic Compounds with Polyatomics
Example: +2 -2
CaSO4
Oxygen is the more electronegative of the two, so it keeps its normal oxidation number.

28. Ionic Compounds with Polyatomics
Example: +2 +6 -2
CaSO4
Sulfur and the four oxygen atoms must add to negative two (the charge of the sulfate anion).

29. Ionic Compounds with Polyatomics
Example:
Pb(OH)4
This is an ionic compound, so the charge of the metal cation is its oxidation number. But this is a transition metal, so we cannot know it from its position on the periodic table.

30. Ionic Compounds with Polyatomics
Example: +4
Pb(OH)4
But the anion, the hydroxide ion, carries a charge of negative one. All four hydroxides are negative one, but since the compound is neutral, the oxidation number of lead must balance it out.

31. Ionic Compounds with Polyatomics
Example: +4 -2
Pb(OH)4
Within the anion, oxygen is the more electronegative of the two elements, and keeps its normal oxidation number.

32. Ionic Compounds with Polyatomics
Example: +4 -2 +1
Pb(OH)4
Within the hydroxide ion, the oxygen and hydrogen must add to the charge of the ion, -1