Empirical vs. Molecular Formulas in Chemistry

Empirical Formula

The simplest whole number ratio of the atoms of each element in the compound.

Molecular Formula

The actual number of atoms of each element in a molecule of the compound.

Hydrogen Peroxide Empirical Formula

HO

Hydrogen Peroxide Molecular Formula

H₂O₂

Glucose Empirical Formula

CH₂O

Glucose Molecular Formula

C₆H₁₂O₆

Ratio of Hydrogen to Oxygen in Hydrogen Peroxide

2:2, which simplifies to 1:1.

Ratio of Carbon to Hydrogen to Oxygen in Glucose

6:12:6, which simplifies to 1:2:1.

Steps to Determine Empirical Formula

1. Determine the mass or mole ratio of each element in the compound. 2. Convert the mass of each element to moles. 3. Divide all the mole amounts by the smallest number of moles to get the simplest whole-number ratio.

How to Determine Molecular Formula

The molecular formula is either given or can be determined if you know the molar mass of the compound.

Relationship between Molecular and Empirical Formula

Molecular Formula = Empirical Formula × n, where n is the factor by which the empirical formula is multiplied.

Key Difference: Definition

Empirical Formula: The simplest whole number ratio of atoms of each element. Molecular Formula: The actual number of atoms of each element in a molecule.

Key Difference: Information Provided

Empirical Formula: Shows the ratio of elements in a compound. Molecular Formula: Shows the actual number of atoms in each molecule.

Key Difference: Example

Empirical Formula of Glucose: CH₂O (simplified ratio). Molecular Formula of Glucose: C₆H₁₂O₆ (actual number of atoms).

Key Difference: Relationship

Empirical Formula can be the same as the molecular formula or a simplified version. Molecular Formula can be a multiple of the empirical formula.

How to Calculate Empirical Formula

1. Determine the mass of each element in the compound. 2. Convert mass to moles using the molar mass of each element. 3. Divide all the mole amounts by the smallest number of moles to get the simplest ratio.

How to Calculate Molecular Formula

If the molar mass of the compound is known, divide the molecular mass by the molar mass of the empirical formula to get the multiplier.

Summary of Empirical Formula

The empirical formula shows the simplest whole number ratio of elements in a compound.

Summary of Molecular Formula

The molecular formula shows the exact number of atoms of each element in a molecule of the compound.

Molecular Formula as a Multiple

The molecular formula can be a multiple of the empirical formula.