An empirical formula shows the smallest whole number ratio of the
atoms
It does not show how many of each atom are in each molecule
All ionic compounds are expressed using empirical formulas
Completely different compounds can have the same empirical
formula:
CH2O can be C6H12O6
(glucose) or C2H4O2 (vinegar) or
even just CH2O (formaldehyde)
What's different is their total molar mass: glucose is 180.18
g/mol, vinegar is 60.06 g/mol and formaldehyde is 30.03 g/mol
See the examples page for
problems showing how to find the empirical formula using a mass percentage
Molecular Formulas
Molecular formulas show exactly how many of each atom is present
in each molecule
Empirical formulas are related to molecular formulas in that the
latter can be found using the former; that is, if you know the
molar mass and the empirical formula you can find out the molecular
formula
If you divide the molar mass of the compound by the formula weight
of the empirical formula you find a factor that can be used to
calculate the molecular formula’ subscripts
Just multiply the subscripts of the empirical formula by the factor
you found; again see the examples page.
Structural Formulas
A structural formula shows the shape of a molecule
Molecules with the same molecular formula can have different structural formulas
These molecules (called isomers) have different properties from one another by virtue of a rearrangement of their constituent atoms
An example is C4H10O which can be 1-butanol, 2-butanol, diethyl ether, or methyl propyl ether.