Oxidation-Reduction Reactions Identifying oxidation states, oxidation numbers, oxidation charges

What is Oxidation-Reduction Reactions? A new reaction type? Oxidation-Reduction Reactions are called Redox reactions. Redox reactions involve the gaining or losing of electrons as reactants form products.

What is Oxidation-Reduction Reactions? A new reaction type? Redox reactions look at the reactants and what happens to their electrons. Reaction types look at patterns of how matter interacts and help predict products.

Are ion charges and oxidation states (charges) the same? Ion charges are due to the gaining and losing of electrons and the particle becomes charged. Oxidation states are assigned to each element in a substance or ion. This may be the same as a charge, but it is technically not the same.

How will we differentiate ion charges and oxidation states (charges)? Ion charges and oxidation states are not the same. To differentiate this, we will write charges as O2- and oxidation states as O-2.

How do we assign oxidation states? What are the guidelines? Oxidation States can be referred to as Oxidation Numbers, or Oxidation Charges. There are a few guidelines to follow to correctly assign oxidation numbers.

Guideline #1: Elemental atoms Atoms in their elemental form always have an oxidation number of ZERO! Ex. H2 : each H atom has an oxidation number of 0. (H0) P4 : each P atom has an oxidation number of 0. (P0) Cu : Cu has an oxidation number of 0. (Cu0)

Guideline #2: Monatomic ions Monatomic ions have the same oxidation number as the ionic charge. Ex. S2- : each S atom has an oxidation number of -2. (S-2) P3- : each P atom has an oxidation number of -3. (P-3) Al : Al has an oxidation number of +3. (Al+3)

Guideline #3: Nonmetals (usually negative, sometimes positive) a. The oxidation number of oxygen is usually -2 in ionic and molecular compounds. The big exception is peroxides. Ex. O2-2 : each O atom has an oxidation number of -1. (O-1) {O22- is a peroxide ion} Al2O3 : Al has an oxidation number of +3 (Al+3) and O has an oxidation number of -2 (O-2)

Guideline #3: Nonmetals (usually negative, sometimes positive) b. The oxidation number of hydrogen is usually +1 when with nonmetals and -1 with metals. Ex. NaH : Na has an oxidation number of +1 (Na+1) and H has an oxidation number of -1 (H-1) HCl : H has an oxidation number of +1 (H+1) and Cl has an oxidation number of -1 (Cl-1)

Guideline #3: Nonmetals (usually negative, sometimes positive) c. The oxidation number of fluorine is always -1. Other halogens have negative oxidation numbers unless with oxygen, then it is positive. Ex. OCl- : Cl has an oxidation number of +1 (Cl+1) and O has an oxidation number of -2 (O-2) HF : H has an oxidation number of +1 (H+1) and F has an oxidation number of -1 (F-1)

Guideline #4: Sum of oxidation numbers The sum of the oxidation numbers of a neutral compound is ZERO! The sum of the oxidation numbers of a polyatomic ion is the charge of the ion. Ex. H3O+ : H has an oxidation number of +1 (H+1) and O has an oxidation number of -2 (O-2). Total is +1 K2O : K has an oxidation number of +1 (K+1) and O has an oxidation number of -2 (O-2)

a. H2S b. S8 c. SCl2 d. Na2SO3 e. SO4-2 f. SO3-2 g. HSO4-1 h. Na2O2 Practice a. H2S b. S8 c. SCl2 d. Na2SO3 e. SO4-2 f. SO3-2 g. HSO4-1 h. Na2O2