Introduction:

There are several ways of showing the formula of a compound:

• Displayed or Structural formula: Shows all atoms and bonds between them
• Condensed formula: Show the atoms and which elements are bonded to each but does not show the bonds
• Molecular formula: Shows only the atoms present in a compound
• Empirical formula: Minimum ratio of the elements in a molecular formula. It is a simplification of the molecular formula. 

Empirical Formula is the minimum whole ratio between the atoms in a molecule expressed in Moles.

Having the % composition as data or the amount of each element in grams in the compound, it is easy to work out the empirical formula:

Steps to calculate the empirical formula: 

1. Find the number of grams of each element, present in the compound. 
2. Convert the mass of each element to moles using the molar mass from the periodic table. (mass /Ar in grams = # of moles)
3. Divide each mole value by the smallest number of moles calculated in 2  to get whole number ratios. 

Example 1:

Calculate the empirical formula for a compound that has 19.60g of Iron and 5.60 g of Oxygen

19.60 g Fe ÷ 56 g Fe/mol = 0.35 /0.35 = 1  ==> Fe₁

5.60 g O     ÷ 16 g O/mol  = 0.35 / 0.35 = 1 ==> O1