Copper oxidizes in air to form the green patina. Oxidation & Reduction Copper oxidizes in air to form the green patina.

Oxidation States Numbers that indicate the general distribution of electrons among bonded atoms in a molecular compound or a polyatomic ion.

Rules for Assigning Oxidation Numbers The oxidation number of any uncombined element is 0. Example: Na(s) = 0

Rules for Assigning Oxidation Numbers The oxidation number of a monatomic ion equals its charge. Example: Cl- is -1

Rules for Assigning Oxidation Numbers The more electronegative element in a binary compound is assigned the number equal to the charge it would have if it were an ion. Example: O in NO is -2

Rules for Assigning Oxidation Numbers The oxidation number of fluorine in a compound is always –1. Example: F in LiF is -1

Rules for Assigning Oxidation Numbers Oxygen has an oxidation number of –2 unless it is combined with F, in which it is +1 or +2, or it is in a peroxide, in which it is –1. Example: O in NO2 is -2

Rules for Assigning Oxidation Numbers Hydrogen’s oxidation state in most of its compounds is +1 unless it is combined with a metal, in which case it is -1 Example: H in LiH is -1 Example: H in HCl is +1

Rules for Assigning Oxidation Numbers In compounds, Group 1 & 2 elements and aluminum have oxidation numbers of +1, +2, and +3 respectively. Example: Ca in CaCO3 is +2

Rules for Assigning Oxidation Numbers The sum of the oxidation numbers of all atoms in a neutral compound is 0. Ca = +2 Example: CaCO3 O = -2 C = +4 1(+2) + 1(+4) + 3(-2) = 0

Rules for Assigning Oxidation Numbers The sum of the oxidation numbers of all atoms in a polyatomic ion equals the charge of the ion. H = +1 Example: H2PO4 - P = +5 O = -2 2(+1) + 1(+5) + 4(-2) = -1

Oxidation States of Vanadium +2 +3 +4 +5

Oxidation Atoms or ions experience an increase in oxidation state. Something whose oxidation number increases is OXIDIZED.

Reduction Atoms or ions experience a decrease in oxidation state. Something whose oxidation number decreases is REDUCED.

2Na(s) +Cl2(g) 2NaCl(s) Na Na+ + e- Oxidation +1 +1 Na Na+ + e- The sodium atom is oxidized to a sodium ion. Its oxidation number INCREASES from 0 to +1.

2Na(s) +Cl2(g) 2NaCl(s) Cl2 + 2e- 2Cl- Reduction -1 -1 Cl2 + 2e- 2Cl- The chlorine atom is reduced to a chlorine ion. Its oxidation number DECREASES from 0 to -1.

Oxidation & Reduction For oxidation to occur during a chemical reaction, reduction must also occur.

Oxidation-Reduction Reaction Any chemical process in which elements undergo changes in oxidation number. Called Redox reaction.

Half Reaction The part of the reaction involving oxidation or reduction alone can be written as a half-reaction. The overall equation is the sum of the two half reactions.

Cu Cu2+ + 2e- 2NO3- + 2e- + 4H+ 2NO2 +2H2O Oxidation Half Reaction Reduction Half Reaction Cu Cu2+ + 2e- 2NO3- + 2e- + 4H+ 2NO2 +2H2O Cu + 2NO3- + 4H+ Cu2+ 2NO2 +2H2O Redox Reaction

REDOX – 1 minute