A chemical formula is a notation used by scientists to show the number and type of atoms present in a molecule, using the atomic symbols and numerical subscripts. A chemical formula is a simple representation, in writing, of a three dimensional molecule that exists. A chemical formula describes a substance, down to the exact atoms which make it up. There are three basic types of chemical formula, the empirical formula, the molecular formula, and the structural formula.

Each one of these chemical formula provide slightly different information about the makeup of a substance, and clues to its three dimensional shape and how it will interact with other molecules, atoms and ions. In a chemical formula, the letters represent the atomic symbol of each atom. The subscript (lower) represents the number of each atom, while the superscript (higher) represents the charge on a given atom. A coefficient before a chemical formula represents that many units of the molecule. Each of the different types of chemical formula is read a little differently.