# What is a molecular formula?

Apr 21, 2014

A molecular formula is an expression that states the number and type of atoms present in a molecule of a substance.

For example, H represents one atom of hydrogen and O represents one atom of oxygen.

If we want to represent two atoms of hydrogen, instead of writing H H, we write H₂. The subscript 2 means that two atoms of the element hydrogen have joined to form a molecule.

We use a subscript only when there is more than one atom of the same element.

For example, a molecule of water contains two atoms of H and one atom of O. We write its molecular formula as H₂O, not H₂O₁.

Examples

There are 6 C atoms and 14 H atoms in a hexane molecule, which has a molecular formula of C₆H₁₄.

Some molecules are big. For example, the molecular formula for human insulin is C₂₅₇H₃₈₃N₆₅O₇₇S₆.