What is an empirical formula?

• A. A formula showing the simplest whole-number ratio of elements
• B. A formula giving the exact count of atoms in the molecule
• C. The same as the molecular formula
• D. The balanced chemical equation

Answer: (A)

The key idea is that an empirical formula shows the simplest whole-number ratio of the elements in a compound, based on experimental data such as percent composition. It doesn’t necessarily tell you the exact number of atoms in a specific molecule—that’s the job of the molecular formula. For example, glucose has an empirical formula of CH2O, even though its molecular formula is C6H12O6. The empirical form is the smallest whole-number ratio, and the molecular form is a multiple of that ratio when the actual molecule contains more than one empirical unit. It’s also not a balanced chemical equation, which describes how substances react.