2. Oxidation-Reaction???? It’s more common than you think……..

3. Oxidation NumbersOxidation Numbers  No physical meaning  Assigned to atoms to aid in redox reactions  Treats all atoms as if they were ions  ACTUAL charge of monoatomic ions, ASSIGNED charge to molecular atoms/atoms with a polyatomic ion

4. Oxidation Number RulesOxidation Number Rules  Priority 1 st, if there is ANY conflict—go with highest priority 1)Sum of oxidation numbers = 0 for ALL neutral compounds (atoms, molecules)  Any single atoms are also assigned oxidation # = 0

5. Rule # 1 ExamplesRule # 1 Examples  Br 2  MgCl 2  C 6 H 12 O 6  Cu  Ag  Fe

6. Oxidation Number RulesOxidation Number Rules 2) Sum of oxidation numbers for an ion = ion’s charge Examples:  SO 4 -2  NH 4 +  Al ion  Cl ion

7. Oxidation Number RulesOxidation Number Rules 3) Group 1A metals = +1 Group 2A metals = +2 Examples: MgSO 4 K 3 PO 4

8. Oxidation Number RulesOxidation Number Rules 4) For the majority of chemical compounds—  F = -1  H = +1 (sometimes will have -1)  O = -2 Examples: NH 3 H 2 O CO HF KF

9. Oxidation Number RulesOxidation Number Rules 5) Group 7A Elements = -1 Group 6A Elements = -2 Group 5A Elements = -3 **When combined with a metal in a binary compound !

10. Rule #5 ExamplesRule #5 Examples  CaF 2  Li 2 S  Mg 3 N  K 3 P

11. Let’s Practice !Let’s Practice !  Strategy: assign oxidation numbers you know 1 st 1)Cr 2 O 7 -2 2)CaH 2 3)KClO 4 4)Fe 3 O 4 5)Al 2 O 3 6)K 2 Cr 2 O 7

13. Oxidation-Reduction Reactions  Electron transfer between ionic compounds, change in oxidation numbers  One compound wants to GIVE electrons, other compound wants to TAKE electrons.

14. 2 chemical processes happening at the same time ! 1) Reduction—  GAIN of electrons in element  Compound becomes more NEGATIVE  DECREASE in oxidation number 2) Oxidation  LOSS of electrons  Compound becomes more POSITIVE  INCREASE in oxidation number

15.  Oxidation CANNOT happen without Reduction.  Reduction CANNOT happen without Oxidation  Both have to happen in a redox reaction ! ! ! (electrons gained = electrons lost)

18. Oxidation Numbers/StateOxidation Numbers/State  Allows us to identify redox reactions  A change in these numbers------ REDOX REACTION ! ! !  Acts like all chemical compounds are ionic----gives atom a charge it would have IF it was ionic

19. How do we identify Redox Reactions?  Assign oxidation numbers to all atoms in the chemical reaction  If there is a CHANGE in the oxidation numbers, the reaction is a REDOX ! ! !

20. Example 1:Example 1:  Mg (s) + Cu (aq) Mg +2 (aq) + Cu (s)

21. Example 2:Example 2:  2 Na + Cl 2  2NaCl  Assign oxidation numbers  Identify where oxidation occurs, where reduction occurs.

22. Redox Reaction? If so, identify what is oxidized and what is reduced. 1)Mg + 2HCl  MgCl 2 + H 2 1)I 2 + 3Cl 2  2 ICl 3 2)NaOH + HCl  NaCl + H 2 O 3)2Na + 2H 2 O  2NaOH + H 2

23. Homework  Read pp. 140-146  Problems p. 142 Exercises 4.7A and 4.7B