The empirical formula represents the simplest whole number ratio for each element in a chemical compound. The first step to finding the empirical formula is to determine how many grams of each element are present in 100 grams. If percentages are provided, then use those numbers to represent the grams of each element in 100 grams of the compound to simplify the procedure.
Texas A&M University states that the grams of each element must be converted into moles using the elements' molar mass, which is the mass of the element divided by its total amount of substance. The molar mass of each element is conveniently found on the periodic table. Once converted, divide the mole values by the smallest number of moles determined from the previous step. Round each number of moles to the closest whole number to find the ratio. If the value is too far from a whole number, multiply the each value by a number that achieves a whole number. These values represent the number of atoms of each element within the compound. The empirical formula written with the elements and these values are written as subscripts.
The empirical formula is used to determine the molecular formula for a compound, as long as the molar mass is known. Simply divide the molar mass of the empirical formula by the molar mass of the compound.