Topic 2 

        

              Oxidation States: A Brief Overview

Oxidation state is a number assigned to an atom in a molecule or ion to indicate the degree of oxidation or reduction of that atom. It represents the hypothetical charge an atom would have if all bonds were ionic.

Rules for Assigning Oxidation States:

  1. Elemental State:

○     Atoms in their elemental state (e.g., H₂, O₂, Cl₂) have an oxidation state of 0.

  1. Monatomic Ions:

○     The oxidation state of a monatomic ion is equal to its charge. For example, Na⁺ has an oxidation state of +1, and Cl⁻ has an oxidation state of -1.

  1. Hydrogen:

○     Hydrogen usually has an oxidation state of +1, except in metal hydrides (e.g., NaH) where it has an oxidation state of -1.

  1. Oxygen:

○     Oxygen usually has an oxidation state of -2, except in peroxides (e.g., H₂O₂) where it has an oxidation state of -1 and in superoxides (e.g., KO₂) where it has an oxidation state of -½.

  1. Fluorine:

○     Fluorine always has an oxidation state of -1 in its compounds.

  1. The Sum of Oxidation States in a Neutral Molecule or Ion:

○     The sum of the oxidation states of all atoms in a neutral molecule must     zero.

○     The sum of the oxidation states of all atoms in a polyatomic ion must equal the charge of the ion.

Examples:

●     In H₂O, the oxidation state of hydrogen is +1 and the oxidation state of oxygen is -2.

●     In SO₄²⁻, the oxidation state of sulfur is +6, and the oxidation state of oxygen is -2.

●     In KMnO₄, the oxidation state of potassium is +1, the oxidation state of manganese is +7, and the oxidation state of oxygen is -2.

Applications of Oxidation States:

●     Balancing redox reactions: Oxidation states help determine the number of electrons transferred in a redox reaction.

●     Predicting the products of reactions: Knowing the oxidation states of elements can help predict the possible products of a chemical reaction.

●     Determining the oxidation number of an element in a compound: Oxidation states can be used to calculate the oxidation number of an element in a complex compound.

By understanding the rules for assigning oxidation states, you can analyze and predict chemical reactions more effectively.