2. Oxidation Process in which atoms or ions attain a more + oxidation state Ex. Na → Na + + e Cl - → Cl + e Ca + → Ca 2+ + e

3. Reduction Atoms or ions of elements attain a more negative oxidation state Ex. Cl + e → Cl - Mnemonic: “OIL RIG” Oxidation involves loss, reduction involves gain

4. Oxidation Number Uncombined elements have oxidation # of 0 Monoatomic ions have oxidation # equal to their ion charge F is always –1 in a compound O is almost always –2 in a compound H is +1 in all compounds except those with metals (then its –1) More electronegative element is assigned a number equal to its ion charge Algebraic sum of oxidation numbers in a compound is always zero

5. Practice Determine the oxidation numbers for each element in the compounds below NaCl H 2 SO 4 AgNO 3 CO 2 SF 6 NO 3 -

6. Definition If oxidation occurs, then reduction must also occur Any chemical process in which elements undergo a change in oxidation number is a Redox reaction

7. Identifying Redox SO 2 + H 2 O + O 2 → H 2 SO 4 NaCl + Ag(NO 3 ) → Na(NO 3 ) + AgCl

8. Practice Determine if each below is a redox reaction SO 3 + H 2 O → H 2 SO 4 2KNO 3 → 2KNO 2 + O 2 H 2 + CuO → Cu + H 2 O

9. More Definitions Reducing Agents – elements that undergo oxidation (the cause reduction in another element) Oxidizing Agents – undergo reduction Mg + Cu(NO 3 ) → Cu + Mg(NO 3 ) Mg is reducing agent – being oxidized Cu 2+ is oxidizing agent – being reduced