Question

Why must the sum of all the oxidation states of the atoms in a neutral molecule be zero?

Short answer

The sum of all the oxidation states of the atoms in a neutral molecule must be zero to maintain charge balance, as a neutral molecule has no net charge. This rule ensures that the total positive and negative charges within the molecule balance out. For example, in water (H₂O), the sum of oxidation states is (+1 x 2) + (-2 x 1) = 0.

Step-by-step solution

Understanding Oxidation States

An oxidation state is a hypothetical charge assigned to an atom in a molecule or ion, representing the atom's apparent degree of electron loss or gain. Oxidation states are used to help understand redox reactions and electron transfer in chemical species.

Charge Balance in a Molecule

A neutral molecule has no net charge, meaning the total positive charge (from protons in the nucleus) and the total negative charge (from electrons) must balance out. This means that the total charge of all the atoms in the molecule must sum up to zero.

Rule for Oxidation States in Neutral Molecules

For any neutral molecule, the sum of the oxidation states of all its atoms must be equal to zero. This rule is based on the fact that a neutral molecule has a charge balance, as explained earlier.

Example: Water (H₂O)

Let's take water (H₂O) as an example of a neutral molecule. The oxidation state of hydrogen (H) is +1, and the oxidation state of oxygen (O) is -2. In a water molecule, there are two hydrogen atoms and one oxygen atom. So, the sum of the oxidation states in a water molecule is: Sum of oxidation states = (2 x +1) + (1 x -2) = +2 -2 = 0 As demonstrated in this example, the sum of oxidation states for atoms in a neutral molecule (H₂O) is equal to zero.