Assignment of Oxidation Numbers Created by Michelle Davis Science Department Chair Lithia Springs High School, GA

1. Elements in their elemental form have an oxidation number of 0. ex) H 2, Cl 2, O 2, Zn, Al, Cu all have an oxidation number = 0 2. The oxidation number of a monatomic ion is the same as its charge. ex) Cl - has oxidation number = -1 Ca 2+ has an oxidation number = 2+ All oxidation numbers must add to zero in a neutral compound or to the overall charge of a charged species!

3. Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Oxygen has an oxidation number of − 2, except in the peroxide ion in which it has an oxidation number of − 1. ex) H 2 O 2 each hydrogen is +1 & each oxygen is -1 Hydrogen is − 1 when bonded to a metal, +1 when bonded to a nonmetal. ex) CaH 2 each calcium is +2 & each hydrogen is -1 H 3 P each hydrogen is +1 & each phosphorus is -3

3. Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Fluorine always has an oxidation number of − 1. The other halogens have an oxidation number of − 1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions. ex) ClO 3 - each oxygen is -2 (last slide) which leaves the chlorine as +5

Assign oxidation numbers to each element in the following compounds: 1)KMnO 4 2)NH 4 Cl 3)Al(NO 3 ) 3 4)N 2 O 4 5)PCl 3 6)C 2 O )K = +1. Mn = +7, O = -2 2)N = -3, H = +1, Cl = -1 3)Al = +3, N = +5, O = -2 4)N = +4, O = -2 5)P = +3, O = -2 6)C = +3, O =-2 Hint: Assign oxygen and hydrogen charges 1 st & then assign the remaining elements their charges!

Brown, T.L., Bursten, B.E., LeMay, Jr., H. E. (2006). Chemistry: The central science. Upper Saddle River, New Jersey: Pearson Education, Inc. Bookstaver, J.D. (2006). Electrochemistry. In Instructor Resource Center for Chemistry: The central science (disk 2, chap.20, lecture presentation). Upper Saddle River, New Jersey: Pearson Education, Inc.