If your chemistry teacher starts to get a little flabby, you want to be sure to help fermium them up

History of Oxidation & Reduction

Reaction types Non-redox reactions – Reactions that do not appear to have an exchange of electrons Redox reactions – Reactions that appear to have an exchange of electrons

Chemiluminescence

Bioluminescence

Fireworks

Photography

OxidationReduction 1772 Lavoisier – when substances burn CH 4(g) + 2O 2(g)  CO 2(g) + H 2 O (l) -corrosion/rusting 4Fe (s) + 3O 2(g)  2Fe 2 O 3 ***Any reaction where reactant combined with oxygen was considered oxidation**** When oxygen was removed from a compound to produce a metal it was called reduction because the mass was lower than the initial amount 2Fe 2 O 3(l) + 3C (s)  4Fe (l) + 3CO 2(g) The process by which a substance lost/gave up electrons Al (s)  Al 3+ (aq) + 3e - The process by which a substance gains electrons Al 3+ (aq) + 3e -  Al (s) Today, oxidation is represented by the increase in (change to a more positive) oxidation number Today, reduction is represented by the decrease in (change to more negative) oxidation number

OIL RIG Oxidation is the loss of electrons Reduction is the gain of electrons ***oxidation & reduction occur at the same time, so #electrons gained = #electrons lost***

Oxidation States The charge an atom would have if both electrons in an electron pair belonged to the most electronegative element in the pair Ex. PotassiumOxygenIron

Oxidation Numbers Rules 1.The oxidation number of an atom in an uncombined element is zero Eg. Fe 2.The sum of the oxidation numbers of the elements in any neutral molecule is zero 3.The sum of the oxidation numbers of the elements in any ion is equal to the charge on the ion eg. NO 3 -

4. Oxidation number of many elements depends on their position on the periodic table a)Elements in group 1 (alkali) are always +1 b)Elements in group 2 (alkaline earths) are always +2 c)Aluminum is always +3 and zinc always +2 d)Halogens are almost always -1 e)Hydrogen has an oxidation number of +1 when combined with non metals f)Oxygen has an oxidation number of -2 in most compounds (except in peroxides) Oxidation Numbers Rules

Example 1 What are the oxidation numbers of each atom in the permanganate ion? (MnO 4 - ) – The sum must be -1 – Oxygen charge is -2 Oxidation of Mn = x 1(x) + 4(-2) = -1 x – 8 = -1 x = x = 7 Oxidation #: Mn = +7 and O = -2

Example 2 What is the oxidation number of each element in potassium dichromate? – Sum must be 0 – Potassium is +1 and Oxygen is -2 2(+1) + 2(x) + 7(-2) = x -14 = 0 2x = 12 x = 6 K = +1O = -2 Cr = +6

If the oxidation number of an atom or ion changes during a chemical reaction, then we know that electron transfer (a redox reaction) has occurred. If the numbers do not change, there is no transfer of electrons and redox does not occur

Example 3 Assign oxidation numbers to each atom and determine whether a redox reaction has taken place for the reaction: CH 4(g) + 2O 2  CO 2(g) + 2H 2 O (g) Lose electrons  oxidized Gain electrons  reduced

Oxidizing agents Take electrons Are reduced themselves Decrease in charge Common oxidizing agents: oxygens, halogens, HNO 3, Cr 2 O 7 2- and MnO 4 -

Reducing Agents Give away electrons Are oxidized themselves Increase in charge Common reducing agents: hydrogen, free metals, hydrocarbons

Example 4 Assign oxidation numbers to each atom and determine whether a redox reaction has taken place. What is the oxidizing agent? Reducing agent? Cu (s) + AgNO 3(aq)  Ag (s) + Cu(NO 3 ) 2(aq)