Compounds and molecules consist of multiple atoms which are bonded together. Chemical formulas describe the type and amount of these atoms.

Take, for instance, the chemical formula of water: H2O. The formula shows that water consists of one oxygen (O) and two hydrogens (H). The number of each element is given as a subscript after each element unless the number is 1 (as for oxygen).

There are three main types of chemical formulas, which contain a varying degree of structural information: