Question

What is an oxidation number? How is it used to identify redox reactions? Explain why, except for ionic compounds, oxidation number does not have any physical significance.

Short answer

The oxidation number (or state) is a concept utilized to keep track of oxidation levels or electron loss in an atom within a chemical compound. It is primarily used to identify electron flow in reactions involving electron transfer, known as redox reactions. In ionic compounds, oxidation numbers represent actual ionic charges and are physically meaningful. But in other compounds, particularly those that are covalently bonded, the oxidation numbers are a purely notional tool used for tracking the movement of electrons in chemical reactions and have no physical significance.

Step-by-step solution

Definition of Oxidation number

The oxidation number (or oxidation state) is an indicator of the degree of oxidation (loss of electrons) for an atom in a chemical compound. This is an arbitrary system used primarily for keeping track of electron flow in redox reactions. They can be assigned to atoms in such a way that the sum of oxidation numbers for all atoms in neutral molecule equals zero.

Explaining the use in redox reactions

In redox reactions, the oxidation state of atoms changes as electrons are transferred between atoms. If the oxidation number of an atom increases during a reaction (loses electrons), it is said to be oxidized. If the oxidation number of an atom decreases in a reaction (gains electrons), it is said to be reduced. Thus, oxidation numbers help us identify and keep track of redox reactions.

Contrasting Oxidation Numbers in Ionic Compounds Vs Other Compounds

In the case of ionic compounds, the oxidation numbers are physically meaningful as they correspond to the actual ionic charges in the compound. However, for covalent compounds that are not ionic in nature, the oxidation numbers are purely a bookkeeping tool. They don't represent real charges on atoms within the molecule, and therefore don't have physical significance beyond their use for tracking electron movement in reactions.