Empirical and Molecular Formula

The empirical formula of a chemical compound is the simplest whole number ratio of atoms of each element present in a compound. 
 *NOTE*: All ionic compounds are empirical formulas.

Ex:  C4H10 (molecular formula of butane) can be reduced to C2H5 (empirical formula)

Ex: What is the empirical formula of a compound containing 11.1% hydrogen and 88.9% oxygen by mass?
Assume you have 100 g.

H: 11.1% x 1 mole/ 1g = 11.1 mol   ---> 1

O: 88.9% x 1mole/ 16g = 55.6 mol --->5

Empirical formula= HO5

Now to write the molecular formula using the empirical formula!

The molecular formula is a multiple of the empirical formula that contains the actual number of atoms that combine to form a molecule.

*To calculate the multiple:  n = molar mass of the compound
                                              molar mass of the empirical formula

Ex: A molecule has an empirical formula of C2H5 and a molar mass of 58 g/mol. What is the molecular formula?

MM C2H5 = 29 g/mol

n = 58g/mol / 29g/mol =2

2 x C2H5 =  C4H10

~ The metal comes first and then the non-metals after are put in alphabetical order~