1. Which elements are present in the compound and the ratio in which they are present. The elements are represented by their chemical symbols, and the subscripts after the symbols indicate the number of atoms of each element in a molecule of the compound. For example, the formula for water, H₂O, tells us that a water molecule contains two hydrogen atoms and one oxygen atom.

2. The relative molecular mass of the compound. This is the sum of the atomic masses of all the atoms in the compound. For example, the relative molecular mass of water is 18 amu (18 atomic mass units), because a molecule of water contains two hydrogen atoms (each with an atomic mass of 1 amu) and one oxygen atom (with an atomic mass of 16 amu).