molecular versus empirical formula what's the difference how do we calculate each of these start at the beginning what's the difference between a molecular formula and an empirical formula a molecular formula is a chemical formula that gives the type of atoms present in that molecule or compound and the number of atoms present in that molecule or compound so think for example of something like water H2O this molecular formula tells me that water the compound water has two hydrogens H2 and one oxygen CO2 for example CO2 that tells me that carbon dioxide has one carbon atom and two oxygen atoms in that compound this is what we call the molecular formula but then what's the empirical formula an empirical formula is basically the simplest version of a formula if you're given the following molecular formula C6H12O6 for those of you that do biology you will recognize that this is the molecular formula for glucose what this molecular formula tells us is that glucose has six carbon atoms 12 hydrogen atoms and six oxygen atoms I can ask you however for the empirical formula of glucose and essentially what I'm asking is for you to simplify the ratio of the atoms so what I have is I have six to to 12 to 6. I can simplify this ratio by finding the biggest number that can divide into all three of these numbers without leaving a remainder or decimal that would be six if I divide each of these by six I get the following one to two to one if I now write my formula c 1 h 2 o one this is what I call my empirical formula for glucose proper definition of empirical formula is the empirical formula is the simplest whole number ratio of atoms within a compound if I for example give you the following molecular formula I have four phosphorus atoms 10 oxygen atoms in this compound and I ask you for the empirical formula I will be simplifying the four to ten ratio what is the biggest number that can divide into four and ten without a remainder two so divide four by two we get p two divide 10 by 2 we get o five we can't simplify that any further so my empirical formula is p205 again it's just the simplest version of the formula but how do we calculate the empirical formula or the simplest version of the formula I'm going to be showing you how to calculate the empirical formula by going from the mass or percentage composition then we will look at how to take our empirical formula and convert it into the molecular formula