5. Sodium loses an electron - oxidation Chlorine gains an electron - reduction

6. Magnesium loses an electron - oxidation Oxygen gains an electron - reduction

7. Oxidation Numbers In order to keep track of electrons during chemical reactions, the idea of oxidation numbers (oxidation states) was introduced.

8. Oxidation Number Is the charge which an atom has, or appears to have, in a compound.

9. Rules for Assigning Oxidation Numbers 1.The oxidation number of any uncombined element is zero.

10. 2. The oxidation number of an ion is the same as its charge.

11. 3. The sum of all the Oxidation numbers in a compound must equal zero. 4. Oxygen always has an oxidation number of -2 except in peroxides ( when it has an oxidation number of -1) and in the compound OF 2 (where it has an oxidation number +2.) 5. Hydrogen is always +1 except in metal hydrides where it is -1.

12. 6. In simple compounds, Halogens have an oxidation number of -1. 7. In a complex ion, the sum of the oxidation numbers should equal the charge on the ion.

13. 1.The oxidation number of any uncombined element is zero. 2. The oxidation number of an ion is the same as its charge. 3. The sum of all the Oxidation numbers in a compound must equal zero. 4. Oxygen always has an oxidation number of -2 except in peroxides ( when it has an oxidation number of -1) and in the compound OF2 (where it has an oxidation number +2.) 5. Hydrogen is always +1 except in metal hydrides where it is -1. 6. In simple compounds, Halogens have an oxidation number of -1. 7. In a complex ion, the sum of the oxidation numbers should equal the charge on the io n.

14. -8 +7 +2-2+2 0 -2 Gains 5e Loses 2e Gains 10e Loses 10e

15. Gains 10e Loses 10e

16. -8 +7 +2 -2 +2 0-2 +2 Gains 5e Loses 2e

17. 0+4 -2 +6 Gains 2electrons Reduction Loses 2e 0 +4 -6+2-2 2 -2+6 -8 +1 Gains 2 electrons Reduced Loses 2e